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Novel proton exchange (PEM) and reverse osmosis (RO) membranes for application in fuel cell and water purification respectively were developed by synthesis and crosslinking of disulfonated biphenol-based poly (arylene ether sulfone)s (BPS). Crosslinking is a prospective option to reduce the water swelling and improve the dimensional stability of hydrophilic BPS copolymers. Several series of controlled molecular weight, phenoxide-endcapped BPS copolymers were synthesized via direct copolymerization of disulfonated activated aromatic halide monomers. The degree of disulfonation was controlled by varying the molar ratio of sulfonated to non-sulfonated dihalide monomers. The molecular weights of the copolymers were controlled by offsetting the stoichiometry between biphenol and the dihalides. Biphenol was utilized in excess to endcap the copolymers with phenoxide groups, so that the phenoxide groups could be further reacted with a suitable crosslinker. Several crosslinking reagents such as methacrylate, multifunctional epoxy, phthalonitrile and phenylethynyls were investigated. A wide range of crosslinking chemistries i.e. free radical (methacrylate), step growth (epoxy), heterocyclic (phthalonitrile) and acetylenic (phenylethynyl) was explored. The effects of crosslinking on network properties as functions of molecular weight and degree of disulfonation of copolymers, crosslinking time and concentration of crosslinker were studied. The crosslinked membranes were characterized in terms of gel fraction, water uptake, swelling, self-diffusion coefficients of water, proton conductivity, methanol permeability, water permeability and salt rejection. In general, all of the crosslinked membranes had lower water uptake and swelling relative to their uncrosslinked counterparts, and less water uptake and volume swelling were correlated with increasing gel fractions. It was possible to shift the percolation threshold for water absorption of BPS copolymers to a higher ion exchange capacity (IEC) value compared to that of the uncrosslinked copolymers by means of crosslinking. This reduced water uptake increased the dimensional stability of higher IEC materials and extended their application for potential PEM or RO membranes. The reduction in water uptake and swelling also increased the effective proton concentration, resulting in no significant change in proton conductivity of the membranes after crosslinking. The self-diffusion coefficients of water and methanol permeability decreased with crosslinking, indicating restricted water and methanol transport. Therefore an improvement in the selectivity (ratio of proton conductivity to water swelling or methanol permeability) of PEMs for application in either H2/air or direct methanol fuel cells was achieved by crosslinking. The epoxy crosslinked BPS copolymers also had significantly enhanced salt rejection with high water permeability when tested in for RO applications. Reductions in salt permeability with increasing crosslinking density suggested that crosslinking inhibited salt transport through the membrane. In addition to the random copolymers, two series of multiblocks endcapped with either a phenoxide-terminated hydrophilic unit or a hydrophobic unit were synthesized and crosslinked with a multifunctional epoxy. Besides the crosslinking study, the effect of sequence distributions of the hydrophilic and hydrophobic blocks in the multiblock copolymers was also investigated. Similar to randoms, crosslinked multiblocks had lower water uptake and swelling but comparable proton conductivities relative to their uncrosslinked analogues. Ph. D.

Low molecular weight liquid polybutadienes (1000 – 2000 g/mol) consisting of 60 mol% 1,2-polybutadiene repeating units were synthesized via anionic telomerization and conventional anionic polymerization. Maintaining the initiation and reaction temperature less than 70 °C minimized chain transfer and enabled the telomerization to occur in a living fashion, which resulted in well-controlled molecular weights and narrow polydispersity indices. MALDI-TOF mass spectrometry confirmed that the liquid polybutadienes synthesized via anionic telomerization contained one benzyl end and one protonated end. Subsequently, 2-ureido-4[1H]-pyrimidone (UPy) quadruple hydrogen-bonding was introduced to telechelic poly(ethylene-co-propylene), and mechanical characterization of the composites with UPy-functionalized carbon nanotubes was performed. The composites enhanced the mechanical properties and the UPy-UPy association between the matrix polymer and carbon nanotubes prevented the decrease of an elongation at break. The matrix polymer was also reinforced without sacrificing the processability. Additionally, UPy groups were introduced to styrene-butadiene rubbers (SBRs). Introducing UPy groups to SBRs drastically changed the physical properties of these materials. Specifically, the SCMHB networks served as mechanically effective crosslinks, which raised Tg and enhanced the mechanical performance of the SBRs. Novel site-specific sulfonated graft copolymers, poly(methyl methacrylate)-g-(poly(sulfonic acid styrene)-b-poly(tert-butyl styrene)), poly(methyl methacrylate)-g-(poly(tert-butyl styrene)-b-poly(sulfonic acid styrene)), and the corresponding sodium sulfonate salts were successfully synthesized via living anionic polymerization, free radical graft copolymerization, and post-sulfonation strategies. The graft copolymers contained approximately 9 – 10 branches on average and 4 wt% of sulfonic acid or sodium sulfonate blocks adjacent to the backbone or at the branch terminus. The mobility of the sulfonated blocks located at the branch termini enabled the sulfonated blocks to more readily interact and form ionic aggregates. The glass transition temperatures (Tg) of the sulfonated graft copolymers with sulfonated blocks at the branch termini were higher than that of copolymers with sulfonated blocks adjacent to the backbone. More facile aggregation of sulfonated blocks at the branch termini resulted in the appearance of ionomer peaks in SAXS whereas ionomer peaks were not observed in sulfonated graft copolymers with sulfonated blocks adjacent to the backbone. In addition, similar analogues, novel site-specific sulfonated graft copolymers, poly(methyl methacrylate)-g-(poly(sulfonic acid styrene)-b-poly(ethylene-co-propylene)) (PMMA-g-SPS-b-PEP), poly(methyl methacrylate)-g-(poly(ethylene-co-propylene)-b-poly(sulfonic acid styrene)) (PMMA-g-PEP-b-SPS), and the corresponding sodium sulfonate salts were successfully synthesized. Estimated ï £N values predicted the phase separation of each block and differential scanning calorimetry (DSC) and dynamic mechanical analysis confirmed the phase separation of each block component of the graft copolymers. The aggregation of sulfonic acid or sodium sulfonate groups at the branch termini restricted the glass transition of the PEP block. This lack of the glass transition of the PEP block resulted in higher storage modulus than a sulfonated graft copolymer with sulfonated blocks adjacent to the backbone. The location of sulfonated blocks in both sulfonic acid and sodium sulfonate graft copolymers significantly affected the thermal, mechanical and morphological properties. Lastly, symmetric (16000 g/mol for each block) and asymmetric (14000 g/mol and 10000 g/mol for each block) poly(ethylene-co-propylene)-b-poly(dimehtylsiloxane) (PEP-b-PDMS) were synthesized using living anionic polymerization and subsequent hydrogenation. The onset of thermal degradation for the PEP-b-PDMS diblock copolymer was higher than 300 ºC and PEP-b-PDMS was more thermally stable than the precursor diblock copolymer, polyisoprene-b-PDMS. DSC analysis of PEP-b-PDMS provided Tg of PDMS -125 ºC, Tg of PEP -60 ºC, Tc of PDMS -90 ºC, and Tm of PDMS -46 and -38 ºC, respectively. Appearance of thermal transitions of each PEP and PDMS block revealed the formation of phase separation. Estimated Ï N also supported the phase separation. Ph. D.

This dissertation discusses topics related to the performance and long-term durability of glass-reinforced composites. The first portion of this dissertation describes work to assess the effect that post-curing has on widely used E-glass/vinyl-ester composites (E-glass/Derakane 510-A and E-glass/Derakane 8084). It is shown that post-curing can have significant positive effects on the initial material properties of glass-reinforced vinyl ester composites. Furthermore, the post-cure of 82ºC for four hours stabilizes the matrix, and as such reduces matrix-related material property evolution. By stopping or nearly stopping material property evolution due to matrix curing over time, the post-cure regime isolates and allows the study of other time-dependent effects, such as fatigue or hygrothermal degradation, and aids designers by establishing an unchanging base set of initial (undamaged) material design properties. The second portion of this dissertation discusses the effects that mean stress and R-ratio have on the fatigue performance of the same material. Qualitative and quantitative differences are seen in the performance as a function of the loading ratio. A residual strength based life prediction model developed at Virginia Tech is applied to the fatigue data, characterizing the material under constant-amplitude loading. Three curve-fitting parameters are then used along with the model to predict variable-amplitude fatigue lives, with remarkably good results. The final portion of the dissertation concerns the effect of hygrothermal and accelerated aging on glass-reinforced composites. A meta-study is performed on data from the literature, and a glass-degradation-based life-prediction model is applied to the data. It is seen that a static fatigue-based activation energy approach to residual strength can predict activation energies associated with glass-reinforced composite strength degradation in the case of glass-reinforced concrete quite well, predicting values of 80-100 kJ/mol, which are similar to those expected for glass dissolution via silica ring opening. The model may also hold some promise for doing the same for glass-reinforced polymer composites. Ph. D.

Polylactide homopolymers with pendent carboxylic acid functional groups have been designed and synthesized to be studied as magnetite nanoparticle dispersion stabilizers. Magnetic nanoparticles are of interest for a variety of biomedical applications including magnetic field-directed drug delivery and magnetic cell separations. Small magnetite nanoparticles are desirable due to their established biocompatibility and superparamagnetic (lack of magnetic hysteresis) behavior. For in-vivo applications, it is important that the magnetic material be coated with biocompatible organic materials to afford dispersion characteristics or to further modify the surfaces of the complexes with biospecific moieties. The acid-functionalized silane endgroup was utilized as the dispersant anchor to adsorb onto magnetite nanoparticle surfaces and allowed the polylactide to extend into various solvents to impart dispersion stability. The homopolymers were complexed with magnetite nanoparticles by electrostatic adsorption of the carboxylates onto the iron oxide surfaces, and these complexes were dispersible in dichloromethane. The polylactide tailblocks extended into the dichloromethane and provided steric repulsion between the magnetite-polymer complexes. The resultant magnetite-polymer complexes were further incorporated into controlled-size nanospheres. The complexes were blended with poly(ethylene oxide-b-D,L-lactide) diblock copolymers to introduce hydrophilicity on the surface of the nanospheres with tailored functionality. Self-assembly of the PEO block to the surface of the nanosphere was established by utilizing an amine terminus on the PEO to react with FITC and noting fluorescence. Ph. D.

The research presented in this dissertation furthers the state of the art for reliability-based design of composite structures subjected to high cycle variable amplitude (spectrum) fatigue loads. The focus is on fatigue analyses for axially loaded fiber reinforced polymer (FRP) composites that contain a significant proportion of fibers in the loading direction and thus have fiber-direction dominated failure. The four papers presented in this dissertation describe the logical progression used to develop an improved reliability-based methodology for fatigue-critical design. Throughout the analysis extensive experimental fatigue data on several material systems was used to verify the assumptions and suggest the path forward. A comparison of 12 fatigue model approaches from the literature showed that a simple linear residual strength approach (Broutman and Sahu) provides an improvement in fatigue life prediction compared to the Palmgren-Miner rule, while more complex residual strength models did not consistently improve on Broutman and Sahu. Evaluation of the effect of load history randomness on fatigue life was made using experimental results for spectra in terms of the first order autocorrelation of the stress events. For approximately reversed Rayleigh distributed fatigue loading, load sequence was not critical in the material behavior. Based on observations of empirical data and evaluation of the micro-mechanics deterioration and failure phenomena of FRP composites under fatigue loading, a new residual strength model for the tension and compression under any load history was proposed. Then this model was implemented in a stochastic framework and a method was proposed to enable calculation of the load and resistance factor design (LRFD) parameters for realistic reliabilities with relatively few computations. The proposed approach has significant advantages over traditional lifetime-damage-sum-based reliability analysis and provides a significant step toward enabling more accurate reliability-based design with composite materials. Ph. D.

The major challenge of the research was to characterize and develop concepts for establishing structure/property relationships between the functionality of the polymer backbone, the states of water and the membrane transport properties. Most of the hydrocarbon based random copolymers reported in the literature show reduced proton conductivity at low water content. This was attributed to the formation of an isolated morphology. Over the last few years our group has synthesized thermally stable multiblock copolymers with varying chemical structures and compositions. Block copolymers consist of two or more incompatible polymers (i.e. blocks) that are chemically conjoined in the same chain. The transport properties of the multiblock copolymers showed a strong dependence on the morphology in contrast to the random copolymers. Irrespective of the nature of the backbone, the transport properties scaled with the block lengths of the copolymers. An increase in block length for a given series of block copolymer was associated with improved proton conduction, particularly under partially hydrated conditions compared to the random copolymers. The structure-property relationship of the proton conductivity and self-diffusion coefficient of water was obtained as a function of the volume fraction of water for all the random and block copolymers. At a given volume fraction, the block copolymers displayed both higher self-diffusion coefficients of water and proton conductivities relative to the random copolymers. This improvement in transport properties indicates the presence of desired and favorable morphology for the blocks. For DMFC applications, the block copolymers also showed low methanol permeability and high selectivity. The states of water in the copolymers were characterized using DSC and NMR relaxation techniques. At similar ionic contents, the free water concentration increased with increasing block lengths. The distribution of the states of water in the copolymers correlates to transport properties. This knowledge, coupled with the state of water experiments, transport measurements, and chemical structure of the copolymers provided a fundamental picture of how the chemical nature of a phase separated copolymer influences its transport properties. The experimental procedure involved impedance spectroscopy, DSC, TGA, FTIR, DMA, pulse gradient stimulated echo (PGSE) NMR, NMR relaxation experiments and various electrochemical fuel cell performance experiments. Ph. D.

Water-based resol phenol formaldehyde, PF, and organic polymeric methylenebis(phenylisocyanate), pMDI, are the two primary choices for the manufacture of exterior grade wood-based composites. This work addresses simple physical blends of pMDI dispersed in PF as a possible hybrid wood adhesive. Part one of this study examined the morphology of hybrid blends prepared using commercially available PF and pMDI. It was found that the blend components rapidly reacted such that the dispersed pMDI droplets became encased in a polymeric membrane. The phase separation created during liquid/liquid blending appeared to have been preserved in the cured, solid-state. However, substantial interdiffusion and copolymerization between blend components also appeared to have occurred according to measured cure rates, dynamic mechanical analysis, and atomic force microscopy. In the second part of this study a series of PF resins was synthesized employing the so-called "split-cook" method, and by using a range of formaldehyde/phenol and NaOH/phenol mole ratios. These neat PF resins were subjected to the following analyses: 1) steady-state flow viscometry, 2) free formaldehyde titration, 3) non-volatile solids determination, 4) size exclusion chromatography, 5) quantitative solution-state ¹³C nuclear magnetic resonance, NMR, 6) differential scanning calorimetry, 7) parallel-plate oscillatory cure rheology, and 8) dielectric spectroscopy. The neat PF analytical results were unremarkable with one exception; NMR revealed that the formaldehyde/phenol mole ratio in one resin substantially differed from the target mole ratio. The neat PF resins were subsequently used to prepare of series of PF/pMDI blends in a ratio of 75 parts PF solids to 25 parts pMDI solids. The resulting PF/pMDI blends were subjected to the following analyses: 1) differential scanning calorimetry, 2) parallel-plate oscillatory cure rheology, and 3) dielectric spectroscopy. Similar to what was inferred in part one of this study, both differential scanning calorimetry (DSC) and oscillation cure rheology demonstrated that cure of the PF continuous phase was substantially altered and accelerated by pMDI. However within actual wood bondlines, dielectric analysis detected little variation in cure speed between any of the formulations, both hybrid and neat PF. Furthermore, the modulated DSC curing experiments detected some latent reactivity in the hybrid system, both during initial isothermal curing and subsequent thermal scanning. The latent reactivity may suggest that a significant diffusion barrier existed between blend components, preventing complete reaction of hybrid blends even after thermal scanning up to 200 °C. Part three of this work examined the bonded wood mode-I fracture performance of hybrid resins as a function of the resol formaldehyde/phenol ratio and also the alkali content. A moderate increase in unweathered fracture toughness was observed for hybrid formulations relative to neat PF. Following accelerated weathering, the durability of the hybrid blends was promising: weathered hybrid toughness was equivalent to that of weathered neat PF. While the resol F/P ratio and alkali content both influenced hybrid fracture toughness, statistical modeling revealed interaction between these variables that complicated result interpretation: the influence of hybrid alkali content depended heavily on each formulation's specific F/P ratio, and vice versa. Master of Science

This research presents a simplified framework for the analysis of deployable trusses using the concentrated strain approach and uses it to provide key insights into the many design decisions to be made in the development of concentrated strain architectures. The framework uses Euler Column Theory to derive closed form solutions to estimate truss performance. The results are compared to a classical solution and shown to give similar results. A range of strut and hinge hierarchy choices are considered. Trusses composed of solid rods with rectangular flexures are shown to have significant axial and bending stiffness reductions due to the smaller cross-sectional areas and lower modulus of the flexures. Trusses composed of tubes are less sensitive to this because the flexure cross-sectional area does not dramatically change from that of the tube. A hinge material metric that properly weights flexure strain and modulus is presented to provide a basis for the comparison and selection of proper hinge materials. However, based on this metric, new materials with higher folding failure strain and higher modulus are needed. Finally, a concentrated strain deployable truss of solid rods was designed, manufactured, and tested. A truss performance index for column loading was used to compare this system with a distributed strain ATK-ABLE GR1 coilable boom system and an articulated ATK-ABLE SRTM boom system. It was demonstrated that the concentrated strain approach has the potential to achieve a higher linear compaction ratio and truss performance index for mass efficient deployable trusses than the distributed strain approach and the articulated approach. Ph. D.

Hydrophilic/hydrophobic block copolymers as proton exchange membranes (PEMs) has become an emerging area of research in recent years. Three series of hydrophilic/hydrophobic, fluorinated/sulfonated multiblock copolymers were synthesized and characterized in this thesis. These copolymers were obtained through moderate temperature (~100°C) coupling reactions, which minimize the ether-ether interchanges between hydrophobic and hydrophilic telechelic oligomers via a nucleophilic aromatic substitution mechanism. The hydrophilic blocks were based on the nucleophilic step polymerization of 3,3′-disulfonated, 4,4′-dichlorodiphenyl sulfone with an excess 4,4′-biphenol to afford phenoxide endgroups. The hydrophobic (fluorinated) blocks were largely based on decafluoro biphenyl (excess) and various bisphenols. The copolymers were obtained in high molecular weights and were solvent cast into tough membranes, which had nanophase separated hydrophilic and hydrophobic regions. The performance and structure-property relationships of these materials were studied and compared to random copolymer systems. NMR results supported that the multiblock sequence had been achieved. They displayed superior proton conductivity, due to the ionic proton conducting channels formed through the self-assembly of the sulfonated blocks. The nano-phase separated morphologies of the copolymer membranes were studied and confirmed by atomic force microscopy. Through control of a variety of parameters, including ion exchange capacity and sequence lengths, performances as high, or even higher than those of the state-of-the-art PEM, Nafion, were achieved. Ph. D.

The commercialization of proton exchange membrane (PEM) fuel cells depends largely upon the development of PEMs whose properties are enhanced over current perfluorinated sulfonic acid PEMs. Understanding how a PEM's molecular weight and morphology affect its relevant performance properties is essential to this effort. Changes in molecular weight were found to have little effect on the phase separated morphologies, water uptake, and proton conductivities of random copolymers. Changes in block length, however, have a pronounced effect on multiblock copolymers, affecting surface and bulk morphologies, water uptake, proton conductivity, and hydrolytic stability, suggesting that multiblock copolymer PEM properties may be optimized by changes in morphology. A major goal of current proton exchange membrane fuel cell research involves developing high temperature membranes that can operate at ~120 °C and low humidites. Multiblock copolymers synthesized from 100% disulfonated poly(arylene ether sulfone) (BPSH100) and naphthalene polyimide (PI) oligomers may be an alternative. At block lengths of ~15 kg/mol they displayed no morphological changes up to 120 °C or even higher. Water desorption was observed to decrease with increasing block length. The copolymers exhibited little to no water loss during a 200 °C isotherm in contrast to random BPSH copolymers and Nafion. A BPSH100-PI multiblock copolymer with large block length appears to have morphological stability and retain water at temperatures exceeding 120 °C, suggesting its candidacy as a high temperature PEM. A growing number of alternative PEM research efforts involve multiblock copolymer chemistries, but little emphasis is placed on the methods used to couple the oligomers. Fluorinated linkage groups can help increase block efficiency during coupling, but their effect on a PEM is not well-known. The choice of linkage type, hexafluorobenzene (HFB) vs. decafluorobiphenyl (DFBP), appears to have small but observable influences on multiblock copolymers with disulfonated and unsulfonated poly(arylene ether sulfone) oligomers. DFBP linkages promote greater phase separation than HFB linkages, resulting in increased stiffness, decreased ductility, and increased proton conductivity at low humidities. DFBP linkages also promote more surface enrichment of fluorine, causing changes in surface morphology and slightly increased water desorption, but determining the impact on actual fuel cell performance requires further research. Ph. D.

The purity of the disulfonated monomer, such as 3,3"-disulfonated-4,4"-dichlorodiphenyl sulfone (SDCDPS), was very important for obtaining high molecular weight copolymers and accurate control of the oligomer's molecular weight. A novel method to characterize the purity of disulfonated monomer, SDCDPS, was developed by using UV-visible spectroscopy. This allowed for utiliziation of the crude SDCDPS directly in the copolymerization to save money, energy, and time. Three series of tert-butylphenyl terminated disulfonated poly(arylene ether sulfone) copolymers (BPSH35, 6FSH35, and 6FSH48) with controlled molecular weightsï¼ Mnï¼ , 20 to 50 kg·mol-1, were successfully prepared by the direct copolymerization method. The molecular weight of the copolymer was controlled by a monofunctional monomer tert-butylphenyl, and characterized by the combination of 1H NMR spectra and modified intrinsic viscosity measurements in NMP with 0.05 M LiBr, which was added to suppress the polyelectrolyte effect. The mechanical properties of the membranes, such as the modulus, strength and elongation at break, were improved by increasing the molecular weights, but water uptake and proton conductivities found insensitive to copolymers" molecular weights. Three series of disulfonated poly(arylene ether ketone) random copolymers have been synthesized and comparatively studied, according to their different chemical structures, for use as proton exchange membranes. The copolymers containing more flexible molecular structures had higher water uptake and proton conductivity than the rigid structures at the same ion exchange capacity. This may be due to the more flexible chemical structures being able to form better phase separated morphology and higher hydration levels. A new hydrophobic-hydrophilic multiblock copolymer has been successfully synthesized based on the careful coupling of a fluorine terminated poly(arylene ether ketone) (6FK) hydrophobic oligomer and a phenoxide terminated disulfonated poly(arylene ether sulfone) (BPSH) hydrophilic oligomer. AFM images and the water diffusion coefficient results confirmed that the multiblock copolymer formed better proton transport channels. This multiblock copolymer showed comparable proton conductivity and fuel cell performance to the Nafion® control and had much better proton transport properties than random ketone copolymers under partially hydrated conditions. This suggested that the multiblock copolymers are promising candidates for proton exchange membranes especially for applications at high temperatures and low relative humidity. Ph. D.

Thin film bilayers and blends composed of polymers and nanoparticles are increasingly important for technological applications that range from space survivable coatings to novel drug delivery systems. Dewetting or spontaneous hole formation in amorphous polymer films and phase separation in multicomponent polymer films can hinder the stability of these systems at elevated temperatures. Hence, fundamental understanding of dewetting and phase separation in polymer/nanoparticle bilayer and blend films is crucial for controlling transport and thermomechanical properties and surface morphologies of these systems. This dissertation provides studies on morphological evolution driven by phase separation and/or dewetting in model polymer/nanoparticle thin film bilayers and blends at elevated temperatures. Morphological evolution in dewetting bilayers of poly(t-butyl acrylate) (PtBA) or polystyrene (PS) and a polyhedral oligomeric silsesquioxane (POSS), trisilanolphenyl-POSS (TPP) is explored at elevated temperatures. The results demonstrate unique dewetting morphologies in both PtBA/TPP and PS/TPP bilayers that are significantly different from those typically observed in dewetting polymer/polymer bilayers. Upon annealing the PtBA/TPP bilayers at 95°C, a two-step dewetting process is observed. PtBA immediately diffuses into the upper TPP layer leading to hole formation and subsequently the holes merge to form interconnected rim structures in the upper TPP layer. Dewetting of both the TPP and PtBA layers at longer annealing times leads to the evolution of scattered holes containing TPP-rich, fractal aggregates. The fractal dimensions of the TPP-rich, fractal aggregates are ~2.2 suggesting fractal pattern formation via cluster-cluster aggregation. Dewetting in PS/TPP bilayers also proceeds via a two-step process; however, the observed dewetting morphologies are dramatically different from those observed in PtBA/TPP bilayers. Cracks immediately form in the upper TPP layer during annealing of PS/TPP bilayers at 200°C. With increasing annealing times, the cracks in the TPP layer act as nucleation sites for dewetting and aggregation of the TPP layer and subsequent dewetting of the underlying PS layer. Complete dewetting of both the TPP and PS layers results in the formation of TPP encapsulated PS droplets. Phase separation in PtBA/TPP thin film blends is investigated as functions of annealing temperature and time. The PtBA/TPP thin film blend system exhibits an upper critical solution temperature (LCST) phase diagram with a critical composition and temperature of 60 wt% PtBA and ~70°C, respectively. Spinodal decomposition (SD) is observed for 60 wt% PtBA blend films and off-critical SD is seen for 58 and 62 wt% PtBA blend films. The temporal evolution of SD in 60 wt% PtBA blend films is also explored. Power law scaling for the characteristic wavevector with time (q ~ t^n with n = -1/4 to -1/3) during the early stages of phase separation yields to domain pinning at the later stages for films annealed at 75, 85, and 95°C. In contrast, domain growth is instantly pinned for films annealed at 105°C. Our work provides an important first step towards understanding how nanoparticles affect polymer thin film stability and this knowledge may be utilized to fabricate surfaces with tunable morphologies via controlled dewetting and/or phase separation. Ph. D.

Amphiphilic tri- and penta-block copolymers containing a polyurethane central block with pendant carboxylic acid groups flanked by hydroxyl functional polyether tails were synthesized. Our intention was to investigate the activities of these copolymers as dispersants for magnetite nanoparticles in biological media. A benzyl alkoxide initiator was utilized to prepare poly(ethylene oxide) (BzO-PEO-OH), poly(propylene oxide) (BzO-PPO-OH) and poly(ethylene oxide-b-propylene oxide) (poly(BzO-EO-b-PO-OH)) oligomeric tail blocks with varying lengths of PEO and PPO. The oligomers had a hydroxyl group at the terminal chain end and a benzyl-protected hydroxyl group at the initiated end. The polyether oligomers were incorporated into a block copolymer with a short polyurethane segment having approximately three carboxylic acid groups per chain. The block co-polyurethane was then hydrogenated to remove the benzyl group and yield primary hydroxyl functionality at the chain ends. End group analysis by 1H NMR showed the targeted ratio of PEO to PPO demonstrating control over block copolymer composition. Number average molecular weights determined by both 1H NMR and GPC were in agreement and close to targeted values demonstrating control over molecular weight. Titrations of the pentablock copolymers showed that the targeted value of approximately three carboxylic acid groups per chain was achieved. Heterobifunctional poly(ethylene oxide) (PEO) and poly(ethylene oxide-b-propylene oxide) (PEO-b-PPO) copolymers were synthesized utilizing heterobifunctional initiators to yield polymers having a hydroxyl group at one chain end and additional moieties at the other chain end. For PEO homopolymers, these moieties include maleimide, vinylsilane, and carboxylic acid functional groups. Heterobifunctional PEO oligomers with a maliemide end group were synthesized utilizing a double metal cyanide coordination catalyst to avoid side reactions that occur with a basic catalyst. PEO oligomers with vinylsilane end groups were synthesized via alkoxide-initiated living ring-opening polymerization, and this produced polymers with narrow molecular weight distributions. Heterobifunctional PEO-b-PPO block copolymers were synthesized in two steps where the double metal cyanide catalyst was used to polymerize propylene oxide (PO) initiated by 3-hydroxypropyltrivinylsilane. The PPO was then utilized as a macroinitiator to polymerize ethylene oxide (EO) with base catalysis. Heterobifunctional PEO and PEO-b-PPO block copolymers possessing carboxylic acid functional groups on one end were synthesized by reacting the vinyl groups with mercaptoacetic acid via an ene-thiol addition. Ph. D.

Magnetic nanoparticles coated with polymers hold great promise as materials for applications in biotechnology. In this body of work, magnetic fluids for the treatment of retinal detachment are examined closely in three regimes; motion of ferrofluid droplets in aqueous media, size analysis of the polymer-iron oxide nanoparticles, and calculation of interparticle potentials as a means for predicting fluid stability. The macromolecular ferrofluids investigated herein are comprised of magnetite nanoparticles coated with tricarboxylate-functional polydimethylsiloxane (PDMS) oligomers. The nanoparticles were formed by reacting stoichiometric concentrations of iron chloride salts with base. After the magnetite particles were prepared, the functional PDMS oligomers were adsorbed onto the nanoparticle surfaces. The motion of ferrofluid droplets in aqueous media was studied using both theoretical modeling and experimental verification. Droplets (~1-2 mm in diameter) of ferrofluid were moved through a viscous aqueous medium by an external magnet of measured field and field gradient. Theoretical calculations were made to approximate the forces on the droplet. Using the force calculations, the times required for the droplet to travel across particular distances were estimated. These estimated times were within close approximation of experimental values. Characterization of the sizes of the nanoparticles was particularly important, since the size of the magnetite core affects the magnetic properties of the system, as well as the long-term stability of the nanoparticles against flocculation. Transmission electron microscopy (TEM) was used to measure the sizes and size distributions of the magnetite cores. Image analyses were conducted on the TEM micrographs to measure the sizes of approximately 6000 particles per sample. Distributions of the diameters of the magnetite cores were determined from this data. A method for calculating the total particle size, including the magnetite core and the adsorbed polymer, in organic dispersions was established. These estimated values were compared to measurements of the entire complex utilizing dynamic light scattering (DLS). Better agreement was found for narrow particle size distributions as opposed to broader distributions. The stability against flocculation of the complexes over time in organic media were examined via modified Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations. DLVO theory allows for predicting the total particle-particle interaction potentials, which include steric and electrostatic repulsions as well as van der Waals and magnetic attractions. The interparticle potentials can be determined as a function of separation of the particle surfaces. At a constant molecular weight of the polymer dispersion stabilizer, these calculations indicated that dispersions of smaller PDMS-magnetite particles should be more stable than those containing larger particles. The rheological characteristics of neat magnetite-PDMS complexes (i.e, no solvent or carrier fluid were present) were measured over time in the absence of an applied magnetic field to probe the expected properties upon storage. The viscosity of a neat ferrofluid increased over the course of a month, indicating that some aggregation occurred. However, this effect could be removed by shearing the fluids at a high rate. This suggests that the particles do not irreversibly flocculate under these conditions. Ph. D.

The primary cause of corrosion in transportation structures is due to chlorides which are applied to bridge decks as deicing salts. The direct cost of corrosion damage to the country's infrastructure is approximately $8.3 billion per year. One of the most common corrosion abatement methods in the United States is the barrier protection implemented through the application of fusion bonded epoxy coatings. The purpose of this study was to investigate various coating and exposure parameters to determine their effects on the corrosion of reinforcing steel. The parameters investigated were: chloride content at the bar depth, coated bar corroded area, corrosion product color under the coating, epoxy coating adhesion, coating color, coating damage (holidays and holes), coating thickness, TGA, DSC and EDS analysis and SEM coating cracking investigation. This was accomplished by testing new coated bar specimens as well as specimens extracted from 27 bridge decks located in Virginia. This study demonstrated the following: The extracted ECR coating samples presented extensive cracking compared to the new ECR samples in which the coating cracking was limited to only one sample. The DSC results showed that both the extracted samples as well as new samples are not fully cured during the manufacturing process. The coating degree of curing data also showed that the bars are insufficiently and unevenly heated prior to the application of the powder coating. Additionally, the samples investigated presented significant permanent adhesion loss with little or no epoxy coating residue present on the bar surface, while the EDS analysis showed that once adhesion is lost, corrosion will proceed unimpeded under the coating even in the absence of chlorides. The parameters that presented a direct correlation with the observed corrosion activity were the number of holidays and the number of damaged areas per unit length of bar. This indicates that the passivation of the bare steel exposed to the concrete pore solution at the breaches in the epoxy coating is not the same as a bare bar under similar exposure conditions allowing it instead to corrode at lower concrete chloride concentration levels than bare bars. The results also show a distinct loss of quality control in the handling and possibly storage of new coated bars. The new ECR samples had significantly higher damage density than the samples extracted from concrete even though the coating is damaged during the placement of the concrete, while there was no change in the number of holidays and cure condition. Finally, the data presented further evidence that while limited, the non-destructive corrosion assessment methods available for bare steel reinforced structures may also be used on ECR reinforced structures. In particular, the corrosion rate measurements correlated reasonably well with the chloride concentrations at bar level. This indicates that while the chlorides may not influence the corrosion activity under the coating, they do influence the corrosion activity at breaches in the coating. Ph. D.

There is a need for multifunctional polymer-particle complexes for use in biomedical applications such as for drug delivery or as MRI contrast agents where composition and stability are essential for the complexes to function. This work outlines a general methodology for rationally designing complexes stabilized with polymer brush layers using adapted star polymer models for brush extension and pair potential. Block copolymer micelles were first utilized for experimental validation by using the brush extension model to predict the size and the interaction model to predict the second virial coefficient, A2. Subsequently, the models were used to predict the size and colloidal stability of magnetite-polymer complexes using the modified Deryaguin-Verwey-Landau-Overbeek theory. Novel hydrophilic triblock copolymers comprised of poly(ethylene oxide) tailblocks and a carboxylic acid containing polyurethane center block were examined by static and dynamic light scattering (SLS and DLS), small angle neutron scattering (SANS), and densiometry. Under conditions when the charge is suppressed such as at low pH and/or high ionic strength, the polymer chains self-assemble into micelles, whereas unimers alone are present under conditions where charge effects are important, such as high pH and low ionic strength. A model for effective interaction between star polymers was used to obtain an expression for the second virial coefficient (A2) for micelles in solution. The values of A2 obtained using this method were compared with experimentally determined values for star polymers and micelles. In doing so, not only was a new means of calculating A2 a priori introduced, but the applicability of star polymer expressions to micellar systems was established. Through the analogy of micelles to sterically stabilized nanoparticles, this model was applied to water-soluble block copolymers adsorbed on magnetite nanoparticles for the purpose of tailoring a steric stabilizing brush layer. The sizes of the magnetite-polymer complexes were predicted using the star polymer model employed for the micelle study with an added layer to account for the anchor block. Colloidal stability was predicted from extended DLVO theory using the pair interaction. This work will lead to a better understanding of how to design ion-containing block copolymers for steric stabilization of metal oxide nanoparticles. Ph. D.

Superparamagnetic Magnetite (Fe3O4) nanoparticles were synthesized and complexed with carboxylate-functionalized block copolymers, and aqueous dispersions of the complexes were investigated as functions of their chemical and morphological structures. The block copolymer dispersants possessed either poly(ethylene oxide), poly(ethylene oxide-co-propylene oxide), or poly(ethylene oxide-b-propylene oxide) outer blocks, and all contained a polyurethane center block with pendant carboxylate functional groups. The complexes were formed through interactions of the carboxylates with the surfaces of the magnetite nanoparticles. Initial efforts utilized an aqueous coprecipitation method for the synthesis of magnetite nanoparticles, which yielded polydisperse magnetite nanoparticles. The nanoparticle complexes were characterized with a range of solution- and solid-state techniques including TGA, XPS, TEM, VSM, DLS and zeta potential measurements. DLVO calculation methods, which sum the contributions from van der Waals, steric, electrostatic and magnetic forces were utilized to examine the interparticle potentials in the presence and absence of external magnetic fields. Compositions were identified wherein a shallow, attractive interparticle potential minimum appears once the magnetic term is applied. This suggested the possibility of tuning the structures of superparamagnetic nanoparticle shells to allow discrete dispersions without a field, yet permit weak flocculation upon exposure to a field. This property has important implications for biomedical applications where movement of particles with an external magnetic field is desirable. In a second study, well-defined, narrow size dispersity magnetite nanoparticles were synthesized via the thermolysis of an iron (III) acetylacetonate (Fe(acac)3) precursor in the presence of benzyl alcohol. The magnetite nanoparticles were coated with triblock and pentablock copolymers possessing poly(ethylene oxide) and poly(propylene oxide-b-ethylene oxide) tailblocks and the carboxylate-functional anchor block. DLVO calculations were applied to the new magnetite particles and diagrams of potential energy versus interparticle distance indicated the predominant effect of steric and magnetic interactions on the particle stability. Exposure of the pentablock copolymer-magnetite complexes in phosphate buffered saline to a 1500 Oe magnetic field with concomitant DLS measurements indicated flocculation of the magnetic nanoparticles. DLS measurements showed increased hydrodynamic radii and scattering intensities with time. Ph. D.

The development, design, and modeling of a rapid continuous processing scheme is developed to economically manufacture conductive polymer composite bipolar plates for fuel cells. Bipolar plates are required to possess several important properties for fuel cell operation, with the most sought after being electrical conductivity and mechanical strength. The polymer composite material generated at Virginia Tech is based on material generated by a wet-lay process and uses polyethylene terepthalate (PET) or polyphenylene sulfide (PPS) as the binder, although PPS is mainly used. In order to reach sufficient conductivity for use in generating bipolar plates, the polymer is doped with high levels of conductive graphite particles in the range of 70-80 wt%. The polymer system is reinforced with 6-9 wt% glass or carbon fibers. When compression molded into a solid, flat preform, the wet-lay material exhibits excellent bulk (in-plane) conductivity (> 250 S/cm). The material also exhibits tensile and flexural strengths of 57.5 and 95.8 MPa, respectively, higher than other polymer composite material being considered for bipolar plate production. However, formability and through-plane conductivity needs improvement. The laminate bipolar plates developed at Virginia Tech are made using wet-lay material in the core and a thermoplastic/graphite mixture on the surfaces. The wet-lay material provides mechanical integrity, while a powder form of PVDF or PPS and graphite mixture added to the surfaces to improve through-plane conductivity and formability. The manufacturing scheme for the production of laminate bipolar plates is based on the pre-consolidation of the wet-lay material, which establishes a solid, flat surface for the continuous addition of laminate powder. Because the laminate powder only requires heating, radiation heating is used in the process design to pre-heat the preform prior to compression molding. The heated preform passes underneath a press, where forming of channels takes place along with cooling of the bipolar plate. It is estimated that the entire process can take one minute to produce a bipolar plate. The cost of manufacturing a bipolar plate is estimated to be $8/kW, below the goal of $10/kW. The annual production is determined to be 250,000, with over 500,000 possible depending on certain design factors. Ph. D.

Poly (caprolactone) (PCL) has been widely studied as a model system for investigating polymer crystallization. In this thesis, PCL crystallization along with other phase transitions in PCL-based polymer blends are studied as Langmuir films at the air/water (A/W) interface. In order to understand the phase behavior of PCL-based blends, surface pressure induced crystallization of PCL in single-component Langmuir monolayers was first studied by Brewster angle microscopy (BAM). PCL crystals observed during film compression exhibit butterfly-shapes. During expansion of the crystallized film, polymer chains detach from the crystals and diffuse back into the monolayer as the crystals "melt". Electron diffraction on Langmuir-Schaefer films suggests that the lamellar crystals are oriented with the chain axes perpendicular to the substrate surface, while atomic force microscopy (AFM) reveals a crystal thickness of ~ 7.6 nm. In addition, the competition between lower segmental mobility and a greater degree of undercooling with increasing molar mass produces a maximum average growth rate at intermediate molar mass. PCL was blended with poly(t-butyl acrylate) (PtBA) to study the influence of PtBA on the morphologies of PCL crystals grown in monolayers. For PCL-rich blends, BAM studies reveal dendritic morphologies of PCL crystals. The thicknesses of the PCL dendrites are ~ 7-8 nm. BAM studies during isobaric area relaxation experiments at different surface pressure reveal morphological transitions from highly branched dendrites, to six-arm dendrites, four-arm dendrites, seaweedlike crystals, and distorted rectangular crystals. In contrast, PCL crystallization is suppressed in PtBA-rich blend films. For immiscible blends of PCL and polystyrene (PS) with intermediate molar masses as Langmuir films, the surface concentration of PCL is the only factor influencing surface pressure below the collapse transition. For PS-rich blends, both BAM and AFM studies reveal that PS nanoparticle aggregates formed at very low surface pressure form networks during film compression. For PCL-rich blends, small PS aggregates serve as heterogeneous nucleation centers for the growth of PCL crystals. During film expansion, BAM images show a gradual change in the surface morphology from highly continuous networklike structures (PS-rich blends) to broken ringlike structures (intermediate composition) to small discontinuous aggregates (PCL-rich blends). Ph. D.

Nanophase-separated hydrophilic-hydrophobic multiblock copolymers are promising proton exchange membrane (PEM) materials due to their ability to form various morphological structures which enhance transport. Four arylene chlorides monomers (2,5-Dichlorobenzophenone and its derivatives) were first successfully synthesized from aluminum chloride-catalyzed, Friedel-Crafts acylation of benzene and various aromatic compounds with 2,5-dichlorobenzoyl chloride. These monomers were then polymerized via Ni (0)-catalyzed coupling reaction to form various high molecular weight substituted poly(2,5-benzophenone)s. Great care must be taken to achieve anhydrous and inert conditions during the reaction. A series of poly(2,5-benzophenone) activated aryl fluoride telechelic oligomers with different block molecular weights were then successfully synthesized by Ni (0)- catalyzed coupling of 2,5-dichloro-benzophenone and the end-capping agent 4-chloro-4'-fluorobenzophenone or 4-chlorophenly-4′-fluorophenyl sulfone. The molecular weights of these oligomers were readily controlled by altering the amount of end-capping agent. These telechelic oligomers (hydrophobic) were then copolymerized with phenoxide terminated disulfonated poly (arylene ether sulfone)s (hydrophilic) by nucleophilic aromatic substitution to form novel hydrophilic-hydrophobic multiblock copolymers. A series of novel multiblock copolymers with number average block lengths ranging from 3,000 to 10,000 g/mol were successfully synthesized. Two separate Tgs were observed via DSC in the transparent multiblock copolymer films when each block length was longer than 6,000 g/mol (6k). Tapping mode atomic force microscopy (AFM) also showed clear nanophase separation between the hydrophilic and hydrophobic domains and the influence of block length, as one increased from 6k to 10k. Transparent and creasable films were solvent-cast and exhibited good proton conductivity and low water uptake. These PAES-PBP multiblock copolymers also showed much less relative humidity (RH) dependence than random sulfonated aromatic copolymers BPSH 35 in proton conductivity, with values that were almost the same as Nafion with decreasing RHs. This phenomenon lies in the fact that this multiblock copolymer possesses a unique co-continuous nanophase separated morphology, as confirmed by AFM and DSC data. Since this unique co-continuous morphology (interconnected channels and networks) dramatically facilitates the proton transport (increase the diffusion coefficient of water), improved proton conductivity under partially hydrated conditions becomes feasible. These multiblock copolymers are therefore considered to be very promising candidates for high temperature proton exchange membranes in fuel cells. Ph. D.

Controlling the surface morphology and degree of crystallinity of poly(L-lactic acid) (PLLA) substrates have recently attracted considerable attention because of their applications in cell adhesion, tissue engineering, and drug delivery. Several techniques have been used to fabricate PLLA substrates, some of which may be invalid because PLLA can degrade during fabrication processes. This dissertation provides the Langmuir-Blodgett (LB) technique as a mechanism for fabricating PLLA substrates at temperatures where PLLA degradation is uncommon. In order to fully understand surface morphologies of PLLA LB-films, studies of Langmuir monolayers at the air/water (A/W) interface using surface pressure-area (Pi-A) isotherm and Brewster angle microscopy (BAM) are vital. PLLA exhibits a first-order liquid expanded to condensed (LE/LC) phase transition with molar mass dependent critical phenomena, the first such observation for a homopolymer Langmuir monolayer. Atomic force microscopy (AFM) images of PLLA LB-films prepared in the LC phase exhibit well-ordered lamellar structures. Molar mass scaling of lamellar dimensions, x-ray reflectivity, and reflection absorption infrared spectroscopy (RAIRS) measurements on PLLA LB-films are consistent with PLLA existing as single molecule 10/3-helices at the A/W interface. Morphologies observed after collapse of the LC monolayer are dependent upon the collapse mechanism and subsequent thermal treatment. For temperatures below the LE/LC critical temperature (Tc), two mechanisms are identified for the formation of three dimensional structures: a buckling and stacking of lamellar monolayers on top of existing lamellae during constant compression rate experiments, and a modified nucleation and growth mechanism during isobaric area relaxation experiments. PLLA LB-films prepared in different Langmuir film phases at temperatures below Tc all contain lamellae with different surface roughnesses and similar helical content. Conventional thermal annealing studies on PLLA LB-films reveal that well-ordered lamellar features are destroyed after annealing the LB-films at bulk crystallization temperature through a melting-recrystallization process, which is confirmed by RAIRS and AFM. Our results may prove useful for studying critical behavior and experimentally testing scaling predictions for two dimensions, the development and testing of theories for crystallization in confined geometries, and separating the roles that roughness and crystallinity play in cell adhesion and spreading on biocompatible polymer surfaces. Ph. D.

Polymer matrix composites are seeing increasing use in structural systems (e.g. ships, bridges) and require a quantitative basis for describing their performance under combined mechanical load and fire. Although much work has been performed to characterize the flammability, fire resistance and toxicity of these composite systems, an understanding of the structural response of sandwich type structures and laminate panels under combined mechanical and thermal loads (simulating fire conditions) is still largely unavailable. Therefore a research effort to develop a model to describe the structural response of these glass/vinyl esters systems under fire loading conditions is relevant to the continuing and future application of polymer matrix composites aboard naval ships. The main goal of the effort presented here is to develop analytical models and finite element analysis methods and tools to predict limit states such as local compression failures due to micro-buckling, residual strength and times to failure for composite laminates at temperatures in the vicinity of the glass transition where failure is controlled by viscoelastic effects. Given the importance of compression loading to a structure subject to fire exposure, the goals of this work are succinctly stated as the:(a)Characterization of the non-linear viscoelastic and viscoplastic response of the E-glass/vinyl ester composite above Tg. (b)Description of the laminate compression mechanics as a function of stress and temperature including viscoelasticity.(c)Viscoelastic stress analysis of a laminated panel ([0/+45/90/-45/0]S) using classical lamination theory (CLT). Three manuscripts constitute this dissertation which is representative of the three steps listed above. First, a detailed characterization of the nonlinear thermoviscoelastic response of Vetrotex 324/Derakane 510A - 40 through Tg was conducted using the Time - Temperature - Stress - Superposition Principle (TTSSP) and Zapas - Crissman model. Second, the modeling approach and viscoelastic relaxation mechanism is validated by substituting the shear relaxation modulus into a compression strength model to predict lifetimes for isothermal and one sided heating of unidirectional laminates. Finally, viscoelastic stress analysis using CLT is performed for a general laminated panel to predict lifetimes under one sided heating. Results indicate that when temperatures remain in the vicinity of Tg, the laminate behavior is controlled by thermoviscoelasticity. Ph. D.

A novel photocrosslinkable and melt processible terpolymer precursor for carbon fibers has been successfully synthesized and characterized. The terpolymer was synthesized by an efficient emulsion polymerization route and has a typical composition of acrylonitrile/ methyl acrylate/acryloyl benzophenone in the molar ratio of 85/14/1. This thesis describes a systematic variation of the polymerization variables in the emulsion polymerization which may further enhance the system. In particular, the effects of chain transfer agent, initiator, and surfactant concentration on the polymer properties were studied. Master of Science

Rheological modification is frequently cited as a key application for hyperbranched polymers. However, the high degree of branching in these polymers restricts entanglement and the resultant mechanical properties suffer. Longer distances between branch points may allow entanglements. Highly branched polymers, where linear units are incorporated between branch points, are synthesized with an oligomeric A2 plus a monomeric B3. Higly branched polymers differ from traditional hyperbranched polymers in that every monomeric repeating unit of a hyperbranched polymer is a potential branch point, which is not true for highly branched polymers. The oligomeric A2 plus B3 synthetic methodology was used for the synthesis of highly branched ionenes and polyurethanes. Highly branched ionenes, which have a quaternary ammonium salt in the main chain, were synthesized with a modified Menshutkin reaction. The oligomeric A2 was comprised of well-defined telechelic tertiary amine endcapped poly(tetramethylene oxide). Reduced mechanical properties were observed for highly branched polymers compared to linear counterparts. Highly branched polyurethanes were synthesized with polyether soft segments including poly(ethylene glycol), poly(tetramethylene glycol), and poly(propylene glycol). Degree of branching was determined via a novel 13C NMR spectroscopy approach, which is described herein. The classical degree of branching was supplemented with an alternative degree of branching equation, which was tailored for highly branched architectures. The melt and solution viscosities of highly branched poly(ether urethane)s were orders of magnitude lower than the linear analogs. For the first time, the presence of entanglements was confirmed for highly branched polymers. Doping the highly branched polyurethane with lithium perchlorate, a metal salt, resulted in a significantly higher melt viscosity. The ionic conductivity of the highly branched polyurethane when doped with a metal salt was orders of magnitude higher than the linear analog. Soybean oil was oxidized for synthesis of soy-based polyol monomers. Three regimes were determined, and for the first time, a correlation between hydroxyl number and a resonance from the double bonds of soybean oil in 1H NMR spectroscopy was described. The relationship was used to accurately describe oxidation of soybean oil with time, temperature, and air flow rate. Soybean oil oxidation was catalyzed, and tack-free films were formed. Ph. D.

Copolymer-cobalt complexes have been formed by thermolysis of dicobalt octacarbonyl in solutions of copolysiloxanes. The copolysiloxane-cobalt complexes formed from toluene solutions of PDMS-b-[PMVS-co-PMTMS] block copolymers were annealed at 600-700 °C under nitrogen to form protective siliceous shells around the nanoparticles. Magnetic measurements after aging for several months in both air and in water suggest that the ceramic coatings do protect the cobalt against oxidation. However, after mechanical grinding, oxidation occurs. The specific saturation magnetization of the siliceous-cobalt nanoparticles increased substantially as a function of annealing temperature, and they have high magnetic moments for particles of this size of 60 emu g⁻¹ Co after heat-treatment at temperatures above 600 °C. The siliceous-cobalt nanoparticles can be re-functionalized with aminopropyltrimethoxysilane by condensing the coupling agent onto the nanoparticle surfaces in anhydrous, refluxing toluene. The concentration of primary amine obtained on the surfaces is in reasonable agreement with the charged concentrations. The surface amine groups can initiate L-lactide and the biodegradable polymer, poly(L-lactide), can be polymerized directly from the surface. The protected cobalt surface can also be re-functionalized with poly(dimethylsiloxane) and poly(ethylene oxide-co-propylene oxide) providing increased versatility for reacting polymers and functional groups onto the siliceous-cobalt nanoparticles.Phthalonitrile containing graft copolysiloxanes were synthesized and investigated as enhanced oxygen impermeable shell precursors for cobalt nanoparticles. The siloxane provided a silica precursor whereas the phthalonitrile provided a graphitic precursor. After pyrolysis, the surfaces were silicon rich and the complexes exhibited a substantial increase in Ms. Early aging data suggests that these complexes are oxidatively stable in air after mechanical grinding. Aqueous dispersions of macromolecule-magnetite complexes are desirable for biomedical applications. A series of vinylsilylpropanol initiators, where the vinyl groups vary from one to three, were prepared and utilized for the synthesis of heterobifunctional poly(ethylene oxide) oligomers with a free hydroxy group on one end and one to three vinylsilyl groups on the other end. The oligomers were further modified with carboxylic acids via ene-thiol addition reactions while preserving the hydroxyl functionality at the opposite terminus. The resulting carboxylic acid heterobifunctional PEO are currently being investigated as possible dispersion stabilizers for magnetite in aqueous media. Ph. D.

The synthesis of a variety of novel functionalized polymers using living polymerization techniques to achieve functional and stimuli responsive coatings on silica surfaces are described. Since microscopic features on a surface influence the overall wetting properties of the surface, a systematic investigation of the influence of polymer architecture on the microscopic characteristics of the modified surfaces was studied using silane-functionalized linear and novel star-branched polystyrene (PS). Star-branched modifiers provide functional and relatively well-defined model systems for probing surface properties compared to ill-defined highly branched systems and synthetically challenging dendrimers. Using these simple star-shaped macromolecules it was shown that the topographies of the polymer-modified surfaces were indeed influenced by the polymer architecture. A model explaining the observed surface features was proposed. A living polymerization strategy was also used to synthesize centrally functionalized amphiphilic triblock copolymers. The amphiphilic copolymers exhibited stimuli responsive changes in surface hydrophobicity. In spite of multiple solvent exposures, the copolymer films remained stable on the surface indicating that the observed changes in surface properties were due to selective solvent induced reversible rearrangement of the copolymer blocks. The chemical composition of the copolymers was tailored in order to tune the response time of the surface anchored polymer chains. Thus, the polymer coatings were used to reversibly change the surface polarities in an on-demand fashion and could find possible applications as smart adhesives, sensors and reusable membrane devices. In contrast to the afore-mentioned covalent modification approach, which often leads to permanent modification of surfaces, renewable surfaces exhibiting "universal" adhesion properties were also obtained through non-covalent modification. By employing hydrogen bonding interactions between DNA bases, surfaces functionalized with adenine groups were found to reversibly associate with thymine-functionalized polymers. This study describing the solvato-reversible polymer coating was the first demonstration on silica surfaces. A systematic investigation of the influence of surface concentration of the multiple hydrogen bonding groups and their structure on the extent of polymer recognition by the modified surfaces is also discussed. Ph. D.

Several types of novel proton exchange membranes which could be used for both direct methanol fuel cells (DMFCs) and hydrogen/air fuel cells were investigated in this work. One of the main challenges for DMFC membranes is high methanol crossover. Nafion, the current perfluorosulfonic acid copolymer benchmark membrane for both DMFCs and hydrogen/air fuel cells, shows very high methanol crossover. Directly copolymerized disulfonated poly(arylene ether sulfone)s copolymers doped with zirconium phosphates and phenyl phosphonates were synthesized and showed a significant reduction in methanol permeability. These copolymer/inorganic nanocomposite hybrid membranes show lower water uptake and conductivity than Nafion and neat poly(arylene ether sulfone)s copolymers, but in some cases have similar or even slightly improved DMFC performance due to the lower methanol permeability. These membranes also show advantages for high temperature applications because of the reinforcing effect of the filler, which helps to maintain the modulus of the membrane, allowing the membrane to maintain proton conductivity even above the hydrated glass transition temperature (Tg) of the copolymer. Sulfonated zirconium phenyl phosphonate additives were also synthesized, and membranes incorporating these materials and disulfonated poly(arylene ether sulfone)s showed promising proton conductivity over a wide range of relative humidities. Single-Tg polymer blend membranes were studied, which incorporated disulfonated poly(arylene ether sulfone) with varied amounts of polybenzimidazole. The polybenzimidazole served to decrease the water uptake and methanol permeability of the membranes, resulting in promising DMFC and hydrogen/air fuel cell performance. Ph. D.

This dissertation describes the past and recent progress in proton exchange membranes (PEM) for fuel cells. In particular the synthesis and characterization of materials for advanced alternative PEM were studied with an emphasis on structure-property and structure-property-performance relationships. The focus has included firstly a one-step synthesis and characterization of 3,3'-disulfonated 4,4'-dichlorodiphenyl sulfone comonomer. The procedure developed is adaptable for industrial-scale commercialization efforts. Secondly, the synthesis of aromatic nitrile containing poly (arylene ether sulfone) random copolymers was demonstrated. Various levels of disulfonation allowed the membrane characteristics to be investigated as a function of the membrane ion exchange capacity. The results favorably compare with the current state-of-the-art (Nafion™), particularly for direct methanol systems (DMFC). Thirdly, the mechanically and thermooxidatively stable copolymer membranes were blended with heteropolyacids producing nanocomposites which have potential in higher temperature fuel cell applications. Lastly, the basic PEM parameters such as water uptake, proton conductivity, and methanol permeabilities were controlled and presented as tunable properties as a function of molecular structure. This was achieved by in-situ control of chemical composition. The direct methanol fuel cell performance (DMFC) was much better than Nafion™. Hydrophobic surface properties of the membranes were improved by partial fluorination which made the Nafion™ bonded electrodes more compatible with the partially fluorinated copolymer membranes. The influence of surface enrichment had two important roles in increasing both initial and long term performance tests. The surface fluorine provided lower contact resistance and lower water uptake. The former was important for the initial tests and the latter provides for better long term performances. A delamination failure mechanism was proposed for the hydrocarbon membrane electrode assemblies (MEA) due to the large difference between water uptake of the catalyst layer and membrane and this was verified by a reduction in high frequency resistance (HFR) for the partially fluorinated systems. This thesis has generated the structure-property and structure-property-performance relationships which will provide direction for the development of next generation (PEM) materials. Ph. D.

An A2 + B3 polymerization for the synthesis of hyperbranched polymers was altered using oligomeric precursors in place of either one or both of the monomer pairs to synthesize highly branched macromolecules. Unique topologies that are intermediates between long-chain branched and hyperbranched structures were obtained and the term "highly branched" was used to define these novel architectures. Various types of highly branched polymers, such as polyurethanes, poly(urethane urea)s, poly(ether ester)s, and poly(arylene ether)s were synthesized using the oligomeric A2 + B3 strategy. The molar mass of the oligomeric precursor permitted the control of the molar mass between branch points, which led to interesting macromolecular properties, such as superior mechanical performance to conventional hyperbranched polymers, disrupted crystallinity, improved processibility, and a multitude of functional end groups. Highly branched poly(urethane urea)s and polyurethanes exhibited microphase-separated morphologies as denoted by dynamic mechanical analysis. The similarity in soft segment glass transition behavior and mechanical properties of the branched systems with that of the linear analogues suggested these materials have considerable promise for a variety of applications. When a polycaprolactone triol was utilized as the B3 oligomer for the synthesis of highly branched polyurethane elastomers, the high degree of branching resulted in a completely amorphous soft segment, whereas the linear analogue with equivalent soft segment molar mass retained the crystallinity of polycaprolactone segment. Oligomeric A2 + B3 methodology was further utilized to tailor the degree of branching of poly(ether ester)s that were developed based on slow addition of dilute solution of poly(ethylene glycol) (PEG) (A2) to a dilute solution of 1,3,5-benzenetricarbonyl trichloride (B3) at room temperature in the presence of triethylamine. A revised definition of the degree of branching was proposed to accurately describe the branched poly(ether ester)s and the degree of branching decreased as the molar mass of the PEG diols was increased. Moreover, branched poly(arylene ether)s were prepared via a similar oligomeric A2 + B3 polymerization of phenol endcapped telechelic poly(arylene ether sulfone) oligomers (A2) and tris(4-fluorophenyl) phosphine oxide (B3) in solution. Highly branched poly(ether ester)s were also synthesized in the melt phase using the oligomeric A2 + B3 polymerization strategy. Melt polymerization effectively limited the cyclization reactions, which are common in A2 + B3 polymerizations in solution, and overcame the need for large amounts of polymerization solvent typical of A2 + B3 systems. Finally, a new family of telechelic polyester ionomers was synthesized based on phosphonium bromide salt end groups and branching allowed the incorporation of higher levels of ionic end groups compared to linear analogues. Ph. D.

Magnetic nanoparticles are of considerable interest owing to their potential applications in biotechnology and the magnetic recording industry. Iron oxides have received much attention owing to their oxidative stability and biocompatibility; however, other transition metals and their alloys are also under investigation. Cobalt has one of the largest magnetic susceptibilities of these materials, but it readily oxidizes upon exposure to air resulting in antiferromagnetic oxide. Hence, coating cobalt nanoparticles with an oxygen-impermeable sheath would confer numerous benefits. Cobalt nanoparticles were prepared by the thermolysis of dicobalt octacarbonyl in two block copolymer micellar systems, wherein the copolymers were precursors to graphite or silica. Subsequent heat treatment of the samples at 600-700oC was conducted to condense the polymer coating around the cobalt nanoparticles and form oxygen impervious graphite or silica sheaths. Magnetic and structural characterization of these novel materials afforded pertinent information about their physical properties. Magnetic susceptometry indicated that the graphite coated cobalt nanoparticles resisted oxidation for over one year. The silica coated cobalt nanoparticles had high saturated specific magnetic moments, but the coatings were brittle and grinding the particles resulted in oxidation over time. Transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and energy-filtered TEM (EFTEM) were employed to study particle size and structural differences of the cobalt nanoparticles before and after heat treatment. The mean particle size and size distribution increased for the graphite coated cobalt particles, due to particle sintering at 700oC. In the silica coated cobalt nanoparticle system, the mean particle size increased when the sample was heat-treated at 600oC leading to a bimodal distribution. This bimodal distribution was explained by a fraction of the particles sintering, while others remained discrete. When the silica system was heat treated at 700oC, the particle size and size distribution remained similar to those of the pre-heat-treated sample, indicating that no sintering had taken place. The rapid pyrolysis of the polymer at 700oC may serve to lock the cobalt nanoparticles into a silica matrix, thus preventing them from coming into contact with one another and sintering. Several diffraction techniques (selected area electron diffraction (SAD), nano-beam electron diffraction (NBD) and x-ray diffraction (XRD)) were used to probe the crystal structure of graphite and silica coated cobalt nanoparticles, which was determined to be predominantly face-centered cubic. Anisotropic magnetic nanoparticles (nanorods) have an increased magnetophoretic mobility over spherical magnetic nanoparticles with the same equatorial radius. This property makes them attractive candidates for in vivo biological applications. Anisotropic mixed ferrite nanoparticles were coated with a biocompatible hydrophilic block copolymer to render them dispersible in aqueous media. Polymer coated mixed ferrite particles exhibited magnetic properties similar to that of pure magnetite, as the total level of other transition metals in the nanoparticulate system was less than 5%. Electron energy loss spectroscopy (EELS) and (EFTEM) confirmed that the dominant elements in the mixed ferrite nanoparticles were iron and oxygen. Furthermore, HRTEM, SAD and XRD analyses indicated that the crystal structure for the mixed ferrite nanoparticles was inverse spinel. X-ray diffraction peaks at low angles for the coated mixed ferrite rods corresponded to poly(ethylene oxide) peaks, suggesting that the block copolymer employed as a dispersant was associated with the particles. Ph. D.

The goal of the research presented in this dissertation was to synthesize novel macromolecular materials that would afford oxidative stability to magnetic cobalt nanoparticles under ambient conditions. The cobalt nanoparticles were formed via the thermolysis of Co2(CO)8 in concentrated solutions of toluene containing the macromolecular dispersion stabilizers. The copolymers were designed to encapsulate the nanoparticles with a number of thin protective coatings to prevent their undesirable oxidation under ambient condtions. Cobalt nanoparticles encased with an organic glass were synthesized by stabilizing cobalt nanoparticles with poly(methyl methacrylate-co-2-vinylpyridine-g-dimethylsiloxane) whereas nanoparticles encapsulated with triazine networks were formed via the thermal treatment of cobalt particles complexed with poly(styrene-b-4-vinylphenylcyanate). Cobalt nanoparticles coated with a combination of carbonaceous and silica char were obtained by pyrolyzing cobalt particles stabilized with poly (4-vinylphenoxyphthalonitrile-co-4-vinylphenoxytriethoxysilane-g-dimethylsiloxane) graft copolymers. Moreover, cobalt nanoparticles encapsulated with either phthalonitrile networks or graphitic char were prepared via the thermal treatment of nanoparticles stabilized with poly(styrene-b-4-vinylphenoxyphthalonitrile). Oxidatively-stable, magnetic cobalt nanoparticle complexes may be prepared by heating cobalt nanoparticles encapsulated in poly(styrene-b-4-vinylphenoxyphthalonitrile) block copolymers at elevated temperatures. The block copolymers were synthesized through the sequential anionic polymerization of styrene and tert-butyldimethylsilyloxystyrene. The silyl ether protecting groups on the second block were hydrolyzed under acidic conditions to afford poly(styrene-b-4-vinylphenol), and the pendent phenols of the diblock copolymer were chemically modified with 4-nitrophthalonitrile to afford poly(styrene-b-4-vinylphenoxyphthalonitrile). Stable suspensions of ~8-10 nm diameter cobalt metal nanoparticles were formed by thermolysis of dicobalt octacarbonyl in solutions of toluene containing poly(styrene-b-4-vinylphenoxyphthalonitrile). The cobalt-polymer nanoparticle complexes were pyrolyzed under argon to afford highly magnetic cobalt nanoparticles encased in graphitic coatings. Magnetic susceptibility measurements indicate that the cobalt-graphitic particles are oxidatively-stable and retain their high saturation magnetizations (~ 95-100 emu g-1) for at least a year under ambient conditions. Ph. D.

The results described in this dissertation have demonstrated several alternative proton exchange membranes (PEM) for hydrogen-air and direct methanol fuel cells (DMFC) that perform as well or better than the state of the art Nafion perfluorosulfonic acid membrane. Direct aromatic nucleophilic substitution polycondensations of disodium 3,3′ S-disulfonate-4,4′ S-difluorodiphenylsulfone (SDFDPS), 4,4′ S-difluorodiphenylsulfone (DFDPS) (or their chlorinated analogs, SDCDPS, DCDPS) and 4,4′ S-thiobisbenzenethiol (TBBT) in the presence of potassium carbonate were investigated. Electrophilic aromatic substitution was employed to synthesize the SDFDPS or SDCDPS comonomers in high yields and purity. High molecular weight disulfonated poly(arylene thioether sulfone) (PATS) copolymers were easily obtained using the SDFDPS monomers, but in general, slower rates and a lower molecular weight copolymer was obtained using the analogous chlorinated monomers. Tough and ductile membranes were solution cast from N,N-dimethylacetamide for both series of copolymers. The degrees of disulfonation (20-50%, PATS 20-50) were controlled by varying the ratio of disulfonated to unsulfonated comonomers. Composite membranes were prepared by homogeneous solution blending the copolymers with phosphotungstic acid (PTA) in dimethylacetamide (DMAc). The composite PATS membranes exhibited moderate PTA molecule water extraction after acidification treatments performed at either room or boiling temperatures. The membranes containing HPA showed improved conductivity at high temperatures (120 °C) and low relative humidities when compared to the pure copolymers. Molecular weight of the copolymers plays a critical role in the overall copolymer physical behavior. It is well known that molecular weight has an enormous impact on practically all of the physical properties of polymeric systems. This dissertation discusses the influence of molecular weight on the characteristics of a specific family of PEM PATS copolymers. This study elucidated that the lower molecular weight materials did indeed behave differently than the higher molecular weight copolymers. Specifically, the water uptake and permeability to methanol decreased with increasing molecular weight. Furthermore, the fully hydrated mechanical properties also improved with molecular weight. The synthesis and fabrication of 45 mole percent disulfonated poly(arylene ether phenyl phosphine oxide diphenyl sulfone) terpolymer-heteropolyacid (HPA) composite membranes and membrane electrode assemblies were chosen for detailed investigation. A series of 45 mole percent disulfonated biphenol-based poly(arylene ether phenyl phosphine oxide diphenyl sulfone) terpolymers (BPSH45-PPO) were also synthesized by nucleophilic aromatic substitution polymerizations. The level of disulfonation was constant at 45 mole percent providing a compromise between high conductivity at low humidity and reasonable mechanical properties in liquid water. The amounts of 4,4′-difluorodiphenyl phenyl phosphine oxide comonomer incorporated into the terpolymer backbone were precisely controlled from 0-50 mole percent relative to the 4,4′-dihalodiphenyl sulfone. Phosphine oxide moieties were employed to enhance the interactions with the PTA relative to the pure copolymer. The composite BPSH45-PPO membranes exhibited lower HPA molecule water extraction after acidification at room and boiling temperatures, which was ascribed to the strong hydrogen and polar interactions between the phosphine oxide moiety and functional groups on the HPA. The membranes containing HPA displayed improved conductivity at high temperatures and low relative humidities when compared to the pure terpolymer samples. The increase of proton conductivity was attributed to the water retention characteristics of the HPA molecules, which allowed enhanced mobility of the protons even at lower humidification levels, providing superior hydrogen-air fuel cell performance. The effect of hexafluoroisopropylidene bisphenol (6FBP) incorporation into 45 mole percent disulfonated poly(arylene ether sulfone) copolymers was investigated. This novel series of directly disulfonated poly(arylene ether sulfone) copolymers with various mole ratios of the 6FBP were synthesized in high molecular weight. The levels of fluorination within the statistically random copolymer architecture were varied from 0-100 mole percent using 6FBP and the correct stoichiometric amount of 4,4′-biphenol. The 6FBP monomer was introduced to decrease the water swelling and improve bonding characteristics with Nafion-bonded electrodes. Indeed, water uptake decreased with increasing incorporation of the 6FBP monomer into the terpolymer. This suggested that the hydrophobic fluorinated material aided in water repulsion of the system. Proton conductivity decreased slightly as the amount of fluorination increased, which was interpreted to be due to the decrease in the ion-exchange capacity. High temperature hydrogen/air fuel cell experiments indicated better Nafion-bonded electrode adhesion for the partially fluorinated materials, as depicted by high temperature (120 °C) and low humidity (50% RH) hydrogen-air fuel cell performance. Investigations into polymeric electromechanical transducers were based on poly(arylene sulfone) ion-exchange membranes bonded between two conductive metal layer electrodes. Imposed deformations and small electric fields allowed similar explorations of both sensing and actuation applications. These copolymers produced larger sensitivities than the benchmark Nafion systems, which was interpreted as being due to their higher hydrated moduli. Methodologies for better defining the morphology of the electrodes were identified to enhance the capacitance and effective interfacial area of the conductive electrodes. The new procedures afforded major improvements to performance and transduction. Transducer actuation at lower frequencies was improved by employing a new direct assembly electrode fabrication technique that suggested a strong correlation between the capacitance and charge motion. Ph. D.

Novel proton exchange membranes (PEMs) were investigated that show potential for operating at higher temperatures in both direct methanol (DMFC) and H2/air PEM fuel cells. The need for thermally stable polymers immediately suggests the possibility of heterocyclic polymers bearing appropriate ion conducting sites. Accordingly, monomers and random disulfonated poly(arylene ether) copolymers containing either naphthalimide, benzoxazole or benzimidazole moieties were synthesized via direct copolymerization. The ion exchange capacity (IEC) was varied by simply changing the ratio of disulfonated monomer to nonsulfonated monomer in the copolymerization step. Water uptake and proton conductivity of cast membranes increased with IEC. The water uptake of these heterocyclic copolymers was lower than that of comparable disulfonated poly(arylene ether) systems, which is a desirable improvement for PEMs. Membrane electrode assemblies were prepared and the initial fuel cell performance of the disulfonated polyimide and polybenzoxazole (PBO) copolymers was very promising at 80 C compared to the state-of-the-art PEM (Nafion®); nevertheless these membranes became brittle under operating conditions. Several series of poly(arylene ether)s based on disodium-3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (S-DCDPS) and a benzimidazole-containing bisphenol were synthesized and afforded copolymers with enhanced stability. Selected properties of these membranes were compared to separately prepared miscible blends of disulfonated poly(arylene ether sulfone) copolymers and polybenzimidazole (PBI). Complexation of the sulfonic acid groups with the PBI structure reduced water swelling and proton conductivity. The enhanced proton conductivity of Nafion® membranes has been proposed to be due to the aggregation of the highly acidic side-chain sulfonic acid sites to form ion channels. A series of side-chain sulfonated poly(arylene ether sulfone) copolymers based on methoxyhydroquinone was synthesized in order to investigate this possible advantage and to couple this with the excellent hydrolytic stability of poly(arylene ether)s. The methoxy groups were deprotected to afford reactive phenolic sites and nucleophilic substitution reactions with functional aryl sulfonates were used to prepare simple aryl or highly acidic fluorinated sulfonated copolymers. The proton conductivity and water sorption of the resulting copolymers increased with the ion exchange capacity, but changing the acidity of the sulfonic acid had no apparent effect. Ph. D.

Polylactide-siloxane triblock copolymers with pendent carboxylic acid functional groups have been designed and synthesized for study as magnetite nanoparticle dispersion stabilizers. Magnetic nanoparticles are of interest in a variety of biomedical applications, including magnetic field-directed drug delivery and magnetic cell separations. Small magnetite nanoparticles are desirable due to their established biocompatibility and superparamagnetic (lack of magnetic hysteresis) behavior. For in-vivo applications it is important that the magnetic material be coated with biocompatible organic materials to afford dispersion characteristics or to further modify the surfaces of the complexes with biospecific moieties. The synthesis of the triblock copolymers is comprised of three reactions. Difunctional, controlled molecular weight polymethylvinylsiloxane oligomers with either aminopropyl or hydroxybutyl endgroups were prepared in ring-opening redistribution reactions. These oligomers were utilized as macroinitiators for ring-opening L-lactide to provide triblock materials with polymethylvinylsiloxane central blocks and poly(L-lactide) endblocks. The molecular weights of the poly(L-lactide) endblocks were controlled by the mass of L-lactide relative to the moles of macroinitiator. The vinyl groups on the polysiloxane center block were further functionalized with carboxylic acid groups by adding mercaptoacetic acid across the pendent double bonds in an ene-thiol free radical reaction. The carboxylic acid functional siloxane central block was designed to bind to the surfaces of magnetite nanoparticles, while the poly(L-lactide)s served as tailblocks to provide dispersion stabilization in solvents for the poly(L-lactide). The copolymers were complexed with magnetite nanoparticles by electrostatic adsorption of the carboxylates onto the iron oxide surfaces and these complexes were dispersible in dichloromethane. The poly(L-lactide) tailblocks extended into the dichloromethane and provided steric repulsion between the magnetite-polymer complexes. Master of Science

Poly(α-hydroxy esters) are a class of biocompatible resorbable polyesters including poly(lactic acid) (PLA) and poly(glycolic acid) (PGA) that are FDA-approved for clinical use. Preliminary tissue culture studies have demonstrated that these poly(α-hydroxy esters) support bone tissue development both in vitro and in vivo, but biocompatibility issues still exist. Tissue scaffolds fabricated from these materials by current methods have biocompatibility limitations because they are chemically and topographically inert to cells. The chemical composition of these scaffolds does not influence cell behavior (i.e. proliferation, differentiation) and their surface topography is on a scale length larger than a cell, which is too large to affect cell adhesion or orientation. It is hypothesized that poly(α-hydroxy ester) tissue scaffolds can be made more bioactive by (1) incorporating poly(ethylene glycol) (PEG) into the polymer interface to promote osteoblastic differentiation and (2) controlling topography to direct cell behavior. The novel processing technique of electrospinning allows the fabrication of nanofiber scaffolds with topographical features the size of focal adhesion contacts capable of influencing cell behavior. Thus, the overall objective of this research project is to characterize electrospun PEG-PLA diblock copolymers as substrates for bone tissue engineering. To accomplish this, PEG-PLLA and PEG-PDLLA diblock copolymers were synthesized with target molecular weights of 42,000 g/mol (PEG:2000, PLLA or PDLLA:40,000). Next, these two polymers and commercially available PLLA and PDLLA were electrospun to form scaffolds with fibers of diameters 0.14 to 2.1 μm. Finally, cell culture studies were performed to characterize cell morphology, proliferation, and osteoblastic differentiation. Results indicate electrospun fiber scaffolds limit cell spreading and persist in cell culture for two weeks. Analysis of cells cultured over 14 days revealed that there were no differences in cell density between polymers with and without PEG. Cell density increased with fiber diameter, indicating that fiber diameter affects cell adhesion and proliferation and suggesting that cells may migrate into scaffolds with large diameter fibers. In contrast to cell density, ALP activity, an indicator of osteoblastic differentiation, was unaffected by fiber diameter. Master of Science

Surface behavior of poly (epsilon-caprolactone) (PCL) have been studied at the air/water interface (A/W). PCL is a hydrophobic and crystalline polyester with a glass transition temperature around -60 degrees centigrade, a melting point around 55 degrees centigrade, excellent biocompatibility, and low toxicity. In the past decade, PCL based systems have attracted considerable interest for controlled-release drug delivery and as scaffolds for tissue engineering, that require a fundamental understanding of PCL's degradation mechanisms and crystallization properties. PCL spherulites were commonly observed in previous bulk studies. This thesis focuses on PCL crystallization in Langmuir monolayers. Brewster angle microscopy (BAM) studies show that square, distorted rectangular, and dendritic crystals form at the A/W interface. While dendritic structures have been observed in poly (ethylene oxide) (PEO) thin film on solid substrates, this study of PCL is the first time that dendritic morphologies have been observed at the A/W interface for a linear flexible-coil polymer. As far as we know, the crystallization of flexible-coil polymers at the A/W interface is a brand new area of research. These findings may provide an interesting model system for studying crystallization in confined geometries and the effect of crystallinity on enzyme catalyzed hydrolysis of this important biodegradable polymer at the A/W interface. The main objectives of this thesis were to investigate the phase behavior of PCL at the A/W interface, gain a deeper understanding of the nucleation and growth mechanism of PCL crystallization at the A/W interface through surface pressure-area isotherms and isobaric area relaxation analyses, and interpret the effects of molecular weight on the nucleation and growth mechanism, and morphologies of semicrystalline PCL crystallized in Langmuir monolayers at the A/W interface. Master of Science

Dimethacrylate monomers containing two cleavable tert-butyl ester groups were synthesized and utilized in the synthesis of star-shaped polymers. Star polymer coupling was achieved by reacting the living poly(alkyl methacrylate) using 2,5-dimethyl-2,5-hexanediol dimethacrylate (DHDMA) or dicumyl dimethacrylate (DCDMA). These starshaped polymers were cleaved under hydrolytic conditions, leading to significant reductions in molecular weights. The cleavable star-shaped polymers also underwent uncatalyzed degradation at elevated temperatures. Pressure-sensitive adhesive (PSA) copolymers based on 2-ethylhexyl acrylate (EHA) were synthesized containing cleavable branching comprised of either DHDMA or DCDMA. Extremely high molecular weight branched polymers were obtained, and these branched adhesives exhibited 180° peel strengths that displayed a strong dependence on the weight-average molecular weights. The PSA branching sites were cleaved via acid-catalyzed hydrolysis, drastically lowering the 1180° peel strengths of the cleaved linear polymers between 75 and 95 percent. Branched poly (EHA) PSAs containing 2-hydroxyethyl methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA), as well as poly(EHA-co-HEMA), were synthesized and modified with photoactive functional groups. Cinnamate functionalized PSAs underwent photocrosslinking under UV light, leading to significant losses in 180° peel strengths. The acrylate functionalized PSAs were mixed with a photoinitiator, and following crosslinking under visible light, these PSAs exhibited excellent deactivation characteristics. Poly(methyl methacrylate) containing aliphatic diols were synthesized via anionic polymerization utilizing the novel protected functional co-initiator 1,1-bis-, 4'-(2-(tertbutyldimethylsilyloxy) ethoxy)phenylethylene (BTOPE). Following the coupling of BTOPE with sec-butyl lithium, methyl methacrylate was polymerized in living fashion at -78 °C in THF. A broad molecular weight range of BTOPE-initiated PMMA samples were synthesized, and molecular weight distributions were as low as 1.03 were observed. Hydrolytic deprotection of the protecting groups resulted in α,α-dihydroxy PMMA. The graft macromonomers poly(tert-butyl styrene-block-styrene) methacrylate and poly(styrene-block-tert-butyl styrene) methacrylate were synthesized from the corresponding diblock copolymer alcohols utilizing acid chloride chemistry. Excellent molecular weight control, narrow molecular weight distributions, and perfect crossover were observed in both types of diblock polymers. The macromonomers were copolymerized with methyl methacrylate via solution free-radical copolymerization. The styrene blocks in the purified graft copolymers were selectively sulfonated using acetyl sulfate. Ph. D.

A series of mixed matrix membranes based on zeolites incorporated into fluorinated polyimides were fabricated and characterized in this study. The first system consisted of a polyimide (6FDA-6FpDA-DABA) with carboxylic acid groups incorporated into its backbone and amine-functionalized zeolite particles (ZSM-2). FTIR indicated that these functional groups interacted with each other through hydrogen bonding. Both SEM and TEM images revealed good contact between the polyimide and the zeolite. Permeability studies showed a drop in He permeability suggesting there were no voids between the two components. While simple gases such as O2 and N2 followed effective permeabilities predicted by mixing theories, polar gases such as CO₂ did not. The second system fabricated used the same polyimide with amine-functionalized zeolite L. This zeolite differs from ZSM-2 in that zeolite L's pores are not clogged with an organic template, and it possesses 1-D pores as opposed to ZSM-2's 3-D pore structure. XPS and zeta potential experiments were performed to verify the presence of amine groups on the zeolite surfaces. FTIR data showed that after a heat treatment, amide linkages were created between the amine group on the zeolite and the carboxylic acid group of the polyimide. SEM images showed a good distribution of zeolite L throughout the polymer matrix, and no indication of voids between the two components. Permeability experiments were performed to determine if the addition of zeolite L to the polyimide improved its separation performance. The permeability was unchanged between the pure polyimide membrane and the mixed matrix membrane, suggesting there were no voids present within the matrix. Permeability results of larger gases followed a Maxwell Model. A third system was prepared using a poly(imide siloxane) (6FDA-6FpDA-PDMS) and untreated zeolite L. The primary focus of this investigation was to determine if the addition of the flexible segment would promote direct contact with the zeolite surface and remove the need to amine-functionalize the zeolite. Poly(imide siloxane)s were synthesized at 0, 22, and 41 wt % PDMS as verified using 1H-NMR. FTIR was employed to qualitatively verify the successful imidization of the polymers. SAXS patterns and TEM images did not reveal distinct phases indicative of phase separation, however, AFM images did show the presence of phase separation of the surfaces of the poly(imide siloxane)s. Permeability results showed a decrease in selectivity and an increase in permeability as the wt % of PDMS was increased. Permeabilities and selectivities dropped as the zeolite loading was increased from 0 to 20 wt %. Upon increasing the zeolite loading from 20 to 30 wt %, increases in permeability were observed, but both the permeability and selectivity were still below that of the pure polymer. The final system studied employed the 41 wt % PDMS poly(imide siloxane) as the polymer matrix and either closed-ended or open-ended carbon nanotubes as the filler. SEM images showed regions of agglomeration for both types of nanotubes. Helium permeability dropped in both types MMMs, but more so in closed-ended carbon nanotubes MMM. Nitrogen permeability was unchanged for the closed-ended carbon nanotubes MMM, and dropped slightly in the open-ended carbon-nanotube MMM. Ph. D.

Coumarin and cinnamate derivatives were positioned as either polymer chain ends or side groups to synthesize photoactive macromolecules and gain the ability to reversibly control molecular weight and crosslink density using UV light. The cinnamates and coumarins were reacted onto the polymers via multiple reaction pathways. Polymers were functionalized with coumarin or cinnamate groups via an esterification reaction between hydroxyl functionalities and an acid chloride derivatized coumarin group. In addition to the esterification reaction, cinnamates were also coupled to polymers via a ring opening reaction between a hydroxyl functionalized cinnamate derivative and a maleic anhydride repeat unit copolymerized into the polymer. Both functional groups undergo a [2π + 2π] photodimerization reaction (coumarin groups in the UVA and cinnamate groups in the UVB), which was utilized to crosslink and chain-extend macromolecules. Coumarin dimers possess the additional ability to photocleave and thus reverse when irradiated at 254 nm. The coumarin reversible photodimerization reaction was utilized to reversibly increase the molecular weight and molecular weight distribution of coumarin-functionalized PEG monols and diols. For example, the number average molecular weight of the coumarin-functionalized PEG diol doubled and the molecular weight distribution increased from 1.08 to 2.75 when exposed to 110 J cm⁻² of UVA irradiation. Subsequent photocleavage (UVC irradiation, 2 J cm⁻²) of the chain-extended PEGs, cleaved coumarin dimers decreasing the molecular weight and molecular weight distribution to their original values. A number of poly(alkyl acrylate) and poly(methyl acrylate) systems were functionalized with coumarin groups to study the effect of the glass transition temperature and alkyl ester side group composition on the photodimerization reaction and subsequent crosslinking. The glass transition temperature (Tg) acted as an on/off switch for the photodimerization reaction. While the absolute difference between Tg and irradiance temperature did not affect the rate or extent of photodimerization reaction, polymers with a Tg greater than the irradiance temperature displayed less reaction than those with a Tg lower than the irradiance temperature. The final extent of conversion was controlled by a complex combination of factors including alkyl ester side chain steric bulkiness. Coumarin-functionalized alkyl acrylates based on ethylhexyl acrylate were tested as detachable PSAs. A 98% decrease in the adhesive peel strength was observed after exposure to UVA irradiation. Cinnamate groups were utilized in the design and synthesis of UV-curable hot melt pressure sensitive adhesives (PSAs). The cinnamate groups were attached to the PSAs to provide a method to increase molecular weight and add a small amount of crosslinking leading to an increase the adhesive strength of the PSAs. Broadband UV irradiation from a laboratory scale industrial lamp increased the peel strength of the adhesives. Postcure of the irradiated cinnamate-functionalized UV-curable hot melt PSAs was reduced compared to photoinitiated free-radical photocurable UV-curable hot melt PSAs. Ph. D.

The chemical modification of low molecular weight novolac oligomers and siloxane/silane-containing monomers has led to novel phthalonitrile derivatives with low glass transition temperatures, ranging from -25 to 75 ºC. Multi-functional, low molecular weight phenol-formaldehyde novolac resins were blended with these novel phthalonitrile derivatives to achieve low viscosity resin blends. Moderate temperatures and rapid curing cycles were employed (200 ºC, 1 h and 225 ºC, 4h) to produce networks with high glass transition temperatures (> 250 ºC). A decrease in the sharp band at 2230 cm⁻¹, attributed to the nitrile functionality of the phthalonitrile resin, was monitored in FTIR studies and indicated the progress of the reactions. Ninety percent conversion was achieved within ~ 30 min. Thermal analysis of siloxane-phthalonitrile/novolac networks cured for 1h at 200 ºC and 4h at 225 ºC did not exhibit glass transition temperatures below 250 ºC. In dynamic TGA studies, 5% weight loss temperatures up to 418 ºC were observed, and the materials exhibited 50 to 56 % char at 800 ºC in nitrogen. Networks prepared from a resin blend containing 50 weight% of a phthalonitrile derivative of a 260 g mol⁻¹ novolac oligomer, 50 weight% of the 260 g mol⁻¹ novolac oligomer, and 1.5 mol % triphenylphosphine (based on novolac) (NOV/NOV/TPP) cured at 200 ºC for 1h, did not exhibit a Tg below 250 ºC via DSC. These networks exhibited a 5% weight loss temperature of 350 ºC, and 70 % char at 800 ºC in TGA studies under nitrogen. This degree of char formation makes these materials appealing for use in carbon-carbon composites. Post-curing these networks at 200 ºC for 1h, and then at 225 ºC for 4h, resulted in high thermo-oxidative stability, with a 5% weight loss observed at 447 ºC and 50 % char at 800 ºC. Blending tetramethyldisiloxane phthalonitrile monomers with 260 g mol⁻¹ novolac oligomers afforded prepolymer resins with low melt viscosities, 560 mPa s at 80 ºC. Such viscosities may allow these resins to be processed via vacuum assisted resin transfer molding (VARTM) at low temperatures and heated at elevated temperatures to produce flame resistant three-dimensional networks. Master of Science

The stable free radical polymerization methodology for production of controlled macromolecules was investigated using a novel monomer, 2-vinylnaphthalene. Initial polymerizations resulted in molecular weight distributions typical of conventional free radical polymerization techniques (>2.0). Manipulation of the initiator concentration and the molar ratio of initiator to nitroxide demonstrated no significant control over the resulting polymer products. Analysis of the polymerization kinetics for a 2-vinylnaphthalene polymerization performed in the presence and absence of the free radical initiator revealed identical monomer consumption profiles as well as pseudo first order kinetics indicating a significant degree of the thermal polymerization was occurring at the polymerization temperature (130°C). Comparison of the thermal polymerization propensity of 2-vinylnaphthalene and styrene revealed an increased tendency for 2-vinylnapthahlene to undergo thermal polymerization. Styrene is considered highly active in its propensity to thermally polymerize. However, an Arhenius analysis using in situ FTIR was employed to determine the activation energy for the thermal polymerization of styrene and 2-vinylnaphthalene. The 2-vinylnaphthalene activation energy for thermal polymerization was determined for the first time to be almost 30 kJ/mol less than styrene. A novel modified Mayo mechanism was proposed for the 2-vinylnaphthalene thermal initiation mechanism. Moreover, this thermal initiation was employed to initiate nitroxide mediated polymerizations of styrene. This first use of a 2-vinylnaphthalene initiating system resulted in polystyrene with a large macrocyclic initiating fragment. The presence of the initiating moiety was studied using both UV-Vis spectroscopy and 1H NMR spectroscopy. The extension of stable free radical polymerization to the acrylate monomer family was examined using a novel nitroxide mediator, N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide (DEPN). The synthesis of DEPN was monitored using in situ FTIR spectroscopy to determine optimum reaction conditions. The purified nitroxide was subsequently employed in the synthesis of various block and random acrylate copolymers. The production of a unique amphiphilic block copolymer consisting of acrylic sequences was achieved. Poly(t-butyl acrylate-b-2ethylhexyl acrylate-b-t-butyl acrylate) was synthesized using the SFRP process. The t-butyl functionalities were subsequently removed in a post-polymerization acid catalyzed hydrolysis. The effect of steric bulk and electronic factors on the resulting SFRP process was also investigated and revealed similar polymerization kinetics for various alkyl acrylates. However, addition of a hydroxyl containing monomer, 2-hydroxyethyl acrylate, resulted in an increase in the polymerization rate up to 2 times. The rate enhancement was attributed to hydrogen bonding effects and this was confirmed using the unprecedented addition of dodecanol, which also demonstrated a significant rate enhancement. Block copolymers were also achieved using a novel difunctional nitroxide synthesized from 4-hydroxy TEMPO and 1,6-hexamethylene diisocyanate. The identity of the nitroxide was confirmed using mass spectrometry and 1H NMR. The dinitroxide was used in the polymerization of styrene and subsequently used to produce symmetric ABA triblock copolymers with t-butyl styrene using a unique two-step polymerization route. In addition, the dinitroxide demonstrated an increased tendency for decomposition due to the complex mediation equilibrium. The decomposition was studied using GPC to evaluate the decomposition effects on the polymerization. Results of the research efforts presented herein are written as individual research reports with contributing authors and pertinent literature reviews presented at the beginning of each chapter. Ph. D.

Poly(dimethylsiloxane) (PDMS) fluids containing magnetite nanoparticles stabilized with carboxylic acid-functionalized PDMS were prepared. PDMS-magnetite complexes were characterized using transmission electron microscopy, elemental analysis, and vibrating sample magnetometry. PDMS-magnetite complexes containing up to 67 wt% magnetite with magnetizations of ~52 emu gram-1 were prepared. The magnetite particles were 7.4 ± 1.7 nm in diameter. Calculations suggested that the complexes prepared using mercaptosuccinic acid-functionalized PDMS (PDMS-6COOH) complexes contained unbound acid groups whereas the mercaptoacetic acid-functionalized PDMS (PDMS-3COOH) complexes did not. Calculations showed that the PDMS-3COOH and PDMS-6COOH covered the same surface area on magnetite. Calculations were supported by molecular models and FTIR analyses. The complexes were dispersed into PDMS carrier fluids by ultrasonication, resulting in magnetic PDMS fluids with potential biomedical applications. Magnetite particles (100 nm to 1 mm in diameter) were prepared by crystallization from goethite/glycol/water solutions under pressure. Two methods for particle growth were investigated in which the crystallization medium was varied by adjusting the amount of water or by adding itaconic acid. Particle surfaces were analyzed by x-ray photoelectron spectroscopy (XPS). Particles with clean surfaces were coated with carboxylic acid-functionalized poly(e-caprolactone) stabilizers. Adding itaconic acid to the reactions afforded particles ~100 nm in diameter. The magnetite particles displayed magnetic hysteresis. The particles were dispersed into vinyl ester resins by ultrasonication and it was demonstrated that the ~100 nm particles remained dispersed for three days without agitation. These dispersions have applications in magnetic induction heating for composite repair. Living polymerizations of hexamethylcyclotrisiloxane were terminated with dimethylchlorosilane, phenylmethylchlorosilane, or diisopropylchlorosilane (DIPCS). Platinum-catalyzed hydrosilation of the hydrosilane-terminated PDMS with allyloxyethanol afforded a systematic series of hydroxyalkyl-terminated PDMS. The reactions were successful except for the hydrosilation of the sterically-hindered DIPCS-functionalized PDMS where no reaction was observed. Hydroxyalkyl-terminated PDMS oligomers were successful in initiating the stannous octoate-catalyzed copolymerization of e-caprolactone, which afforded PDMS-b-PCL diblock copolymers of controlled composition. Ph. D.

The objective of the research described in this thesis has been to improve the toughness of phenolic networks while maintaining flame resistance. A four step synthetic scheme has been developed to prepare 4,4′-Bis(3,4-dicyanophenoxy)biphenyl(biphenoxyphthalonitrile). A 700 g mol-1 novolac oligomer was cured with relatively low concentrations of this reagent (~20 wt %) into high Tg (~190 °C) networks. The curing reaction was attrubuted to nucleophilic attack of the phenolic hydroxyl on the nitrile groups of the phthalonitrile resulting in the formation of heterocylic rings. TGA and cone calorimetry demonstrated that these networks have excellent thermo-oxidative stability. Further goals were to develop halogen-free, flame retardant monomers for improving the thermo-oxidative resistance of polystyrene and dimethylacrlyate/styrene(vinyl ester) networks. 4-Vinylphenoxyphthalonitrile, a phthalonitrile derivative of styrene, was synthesized. FTIR has been utilized to demonstrate this new monomer co-cured into vinyl ester networks in free radical thermosetting polymerizations. Upon post-curing the networks between 200-260 °C for ~1.5 h, the nitrile groups reacted to form heterocyclic crosslinks. TGA and cone calorimetry demonstrated that the 4-vinylphenoxyphthalonitrile substantially improved the flame resistance of vinyl ester networks. Copolymerizations of styrene and 4-vinylphenoxyphthalonitrile were conducted at 75 °C for 24 h using 0.5 wt % AIBN in chlorobenzene. Dynamic TGA at 10 °C min-1 in air showed that copolymers containing 10 and 25 mole % of 4-vinylphenoxyphthalonitrile had increased initial weight loss temperatures in air by (~50 °C higher) and increased the char yield between 400-600 °C. High molecular weight nitrile-functional, (hexafluoroisopropylidene)diphenol based aromatic poly(arylene ether)s with pendent sulfonic acid groups were prepared by nucleophilic step copolymerization of 4,4′-(hexafluoroisopropylidene)diphenol, 2,6-dichlorobenzonitrile, and 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone under basic conditions in N-methyl-2-pyrrolidinone at 200 °C. A series of these materials with systematically varied concentrations of the sulfonic acid moieties showed increased glass transition temperatures, proton conductivities, and hydrophilicities as a function of disulfonation. Atomic force microscopy (AFM) demonstrated that the acidified copolymer with 35 mole % of disulfonated units was phase separated into a co-continuous morphology of hydrophobic and hydrophilic domains. Ph. D.

Poly(dimethylsiloxane-b-methylvinylsiloxane) (PDMS-b-PMVS) diblock copolymers were synthesized via anionic living polymerization with controlled molecular weights and narrow molecular weight distributions. Targeted molecular weights agreed well with experimental values determined by 1H NMR, 29Si NMR, and GPC. Morphologies were investigated by DSC to analyze glass transition temperatures. Only one Tg was observed for each PDMS-b-PMVS block copolymer suggesting that the blocks were miscible in bulk. Tg's ranged from approximately -126 to -128 °C and were between the Tg's of the PDMS (-123 °C) and PMVS (-137 °C) homopolymers. The PMVS blocks were functionalized with trimethoxysilethyl or triethoxysilethyl pendent groups via hydrosilations to yield poly(dimethylsiloxane-b-[poly(methylvinyl)-co-(methyl-(2-trimethoxysilethyl)siloxane)] (PDMS-b-[PMVS-co-PMTMS]) or poly(dimethylsiloxane-b-[poly(methylvinyl)-co-(methyl-(2-triethoxysilethyl)siloxane)] (PDMS-b-[PMVS-co-PMTES]) copolymers, respectively. The PMVS blocks were either derivatized with the functional groups or half of the repeat units were functionalized. The fully hydrosilated materials were diblock copolymers, and the materials that were 50% hydrosilated had a random sequence of methylvinylsiloxy units and methyl-(trialkoxysilethyl)siloxy units. The PDMS-b-[PMVS-co-PMTES] block copolymers had Tg's ranging from -124 to -126 °C and only one Tg was observed. Surface tension measurements suggested that PDMS-b-[PMVS-co-PMTES] copolymers formed aggregates in toluene. Stable suspensions of superparamagnetic cobalt nanoparticles were prepared in toluene in the presence of PDMS-b-[PMVS-co-PMTMS] or PDMS-b-[PMVS-co-PMTES] copolymers via thermolysis of Co2(CO)8. It is hypothesized that the block copolymers functioned as micellar templates for the cobalt nanoparticles. TEM micrographs showed non-aggregated cobalt nanoparticles coated with copolymers that had mean particle diameters ranging from ≥10-15 nm. Specific saturation magnetizations of these cobalt-copolymer complexes ranged from 90-110 emu g-1 Co, comparable to literature values for this particle size. Master of Science

Poly(ethylene terephthalate) (PET) is an important commercial polyester and widely used as fibers, packagings, containers and engineering materials. It is believed that the incorporation of a low level of ionic groups into PETs dramatically improves the mechanical performance and compatibility with other substrates. However, polymers containing ionic groups always exhibit complicated behavior due to the presence of ionic aggregates in the organic matrix, and this thesis investigates the effect of backbone architectures on the properties of PET ionomers in detail. Three series of random and telechelic PET ionomers with equivalent molecular weights and ionic contents were synthesized using conventional melt polymerization. Solid state sodium NMR spectroscopy and melt rheological analysis demonstrated that the stability of ionic aggregates of telechelic ionomers decreased dramatically with an increase in temperature. A slightly branched structure resulted in high molecular weight ionomers bearing more than two ionic end groups. However, when the level of the branching reagent was lower than 3 mol%, the ionomers with flexible backbone (poly (ethylene terephthalate-co-ethylene isophthalate)) tended to form a high fraction of intramolecular aggregates at high temperatures. When the level of branching agent was higher than 3 mol%, the compact structures led to strong intermolecular aggregates. PEG endcapped PET and PET random ionomers were synthesized to investigate the effect of PEG end groups on the morphology and rheology of PET and PET ionomers. A small fraction of incorporated PEG end groups increased PET crystallization rate dramatically. Moreover, the PEG endgroups tended to aggregate on the surface of PET to result in a PEG rich layer, which improved the biocompatibility and decreased protein adhesion. The PEG end groups also plasticed the ionic clusters of PET ionomers to decrease melt viscosity, and resulted in a water soluble polyester. Hyperbranched polymers contain a well-defined plurality of peripheral functionalities. These functionalities subsequently serve as sites for further chemical modification or as templates for noncovalent intermolecular association. In most cases, hyperbranched polymers are prepared using a one-step polymerization process involving ABn monomers. A novel AB2 monomer, 4-(fluorophenyl)-4',4"-(bishydroxyphenyl) phosphine oxide, was synthesized. The monomer was successfully polymerized to a modest molecular weight with various catalysts, including K₂CO₃ and Cs₂CO₃/Mg(OH)₂. Moreover, an efficient approach to hyperbranched polyarylates via the polymerization of A2 and B3 monomers without gelation was also developed. A dilute bisphenol A (A2) solution was added slowly to a dilute 1,3,5-benzenetricarbonyl trichloride (B3) solution at 25 °C to prepare hyperbranched polyarylates in the absence of gelation. Ph. D.

Polymer matrix composites (PMC's) perform well under many loading conditions and situations. Exposure of PMC's to fire is a concern due to their inherent material degradation at elevated temperatures. The elevated temperature response of PMC's to combined thermal and mechanical loads are especially of concern. PMC thermal and mechanical properties undergo transformations at elevated temperatures. Some of these effects are reversible if the maximum temperatures are lower than approximately 200C. The stiffness is significantly reduced at elevated temperatures but if the applied temperature is under the thermal degradation temperature of the matrix, the stiffness should be recoverable upon cooling. Some effects like the endothermic decomposition of the matrix are not reversible effects. This study focuses on reversible properties in the temperature range from room temperature to about 200C. Thermally these effects alter the thermal conductivity and specific heat. Reversible elastic effects considered are the off axis stiffness reductions as functions of temperatures. Thermal profile predictions were conducted using a finite difference code that included convection and radiation effects on the front and back faces of the composite. These predictions were shown to be in good agreement with experimental data. A modified classic laminate analysis (CLT) was implemented to predict the failure times of the composites under combined thermal and mechanical loading. The Budiansky-Fleck micro-buckling analysis technique was used as the failure function of the [0] surface plies. A finite element analysis (FEA) analysis was also performed and showed good agreement with the experimental data. Master of Science

A designed series of directly copolymerized homo- and disulfonated copolymers containing controlled degrees of pendant sulfonic acid groups have been synthesized via nucleophilic step polymerization. Novel sulfonated poly (arylene ether sulfone) copolymers using 4,4'-bisphenol A, 4,4'-biphenol, hexafluorinated (6F) bisphenol AF, and hydroquinone, respectively, with dichlorodiphenyl sulfone (DCDPS) and 3,3'-disodiumsulfonyl-4,4'-dichlorodiphenylsulfone (SDCDPS) were investigated. Molar ratios of DCDPS and SDCDPS were systematically varied to produce copolymers of controlled compositions, which contained up to 70 mol% of disulfonic acid moiety. The goal is to identify thermally, hydrolytically, and oxidatively stable high molecular weight, film-forming, ductile ion conducting copolymers, which had properties desirable for proton exchange membranes (PEM) in fuel cells. Commercially available bisphenols were selected to produce cost effective alternative PEMs. Partially aliphatic bisphenol A and hexafluorinated (6F) bisphenol AF produced amorphous copolymers with different thermal oxidative and surface properties. Biphenol and hydroquinone was utilized to produce wholly aromatic copolymers. The sulfonated copolymers were prepared in the sodium-salt form and converted to the acid moiety via two different methodologies and subsequently investigated as proton exchange membranes for fuel cells. Hydrophilicity increased with the level of disulfonation, as expected. Moreover, water sorption increased with increasing mole percent incorporation of SDCDPS. The copolymers' water uptake was a function of both bisphenol structure and degree of disulfonation. Furthermore, the acidification procedures were shown to influence the Tg values, water uptake, and conductivity of the copolymers. Atomic force microscopy (AFM) in the tapping mode confirmed that the morphology of the copolymers could be designed to display nanophase separation in the hydrophobic and hydrophilic (sulfonated) regions. Morphology with either co-continuous hydrophobic or hydrophilic domains could be attained for all the sulfonated copolymers. The degree of disulfonation required for continuity of the hydrophilic phase varied with biphenol structure. Proton conductivity values for the sulfonated copolymers, under fully hydrated conditions, were a function of bisphenol and degree of sulfonation. However, at equivalent ion exchange capacities the proton conductivities were comparable. A careful balance of copolymer composition and acidification method was necessary to afford a morphology that produced ductile films, which were also sufficiently proton conductive. The copolymers of optimum design produced values of 0.1 S/cm or higher, which were comparable to the commercial polyperfluorosulfonic acid material Nafion™ control. Ph. D.

One of the major classes of polymer matrix resins under consideration for structural composite applications in the infrastructure and construction industries is vinyl ester resin. Vinyl ester resin is comprised of low molecular weight poly(hydroxyether) oligomers with methacrylate endgroups diluted with styrene monomer. The methacrylate endgroups cure with styrene via free radical copolymerization to yield thermoset networks. The copolymerization behavior of these networks was monitored by Fourier Transform Infrared Spectroscopy (FTIR) at various cure conditions. Reactions of the carbon-carbon double bonds of the methacrylate (943 cm-1) and styrene (910 cm-1) were followed independently. Oligomers possessing number average molecular weights of 700 g/mole were studied with systematically increasing levels of styrene. The Mortimer-Tidwell reactivity ratios indicated that at low conversion more styrene was incorporated into the network at lower cure temperatures. The experimental vinyl ester-styrene network compositions deviated significantly from those predicted by the Meyer-Lowry integrated copolymer equation at higher conversion, implying that the reactivity ratios for these networks may change with conversion. The kinetic data were used to provide additional insight into the physical and mechanical properties of these materials. In addition to establishing the copolymerization kinetics of these materials, the development of halogen free fiber reinforced vinyl ester composites exhibiting good flame properties was of interest. Flame retardant vinyl ester resins are used by many industries for applications requiring good thermal resistance. The current flame-retardant technology is dependent on brominated vinyl esters, which generate high levels of smoke and carbon monoxide. A series of halogen free binder systems has been developed and dispersed in the vinyl ester to improve flame retardance. The binder approach enables the vinyl ester resin to maintain its low temperature viscosity so that fabrication of composites via Vacuum Assisted Resin Transfer Molding (VARTM) is possible. The first binder system investigated was a polycaprolactone layered silicate nanocomposite, which was prepared via intercalative polymerization. Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) data indicated a mixed morphology of exfoliated and intercalated structures. The mechanical properties and the normalized peak heat release rates were comparable to the neat vinyl ester resin. Alternative binder systems possessing inherent flame retardance were also investigated. A series of binders comprised of novolac, bisphenol A diphosphate, and montmorillonite clay were developed and dispersed into the vinyl ester matrix. Cone calorimetry showed reductions in the peak heat release rate comparable to the brominated resin. Ph. D.

Reactivity ratios for the homogeneous free radical initiated copolymerization of acrylonitrile and methyl acrylate were measured by NMR on isolated, low conversion copolymers and by real time in situ FTIR. The system utilized azobisisobutyronitrile (AIBN) initiator in dimethyl formamide (DMF) at 62°. The FTIR technique allowed rapid generation of extensive copolymer compositions, which permitted application of nonlinear least squares methodology for the first time to this copolymer system. Thus, reactivity ratios at the 95% confidence level were determined to be 1.29 ± 0.2 and 0.96 ± 0.2 for acrylonitrile and methyl acrylate, respectively. The results are useful for the development of acrylonitrile (

The scope of this research entailed the synthesis of novel polyorganosiloxanes with pendent phosphine, phosphine oxide, nitrile and carboxylic acid moieties. Such polysiloxanes were prepared with controlled concentrations of both the polar moieties and hydrido or vinyl pendent crosslinkable sites to afford precursor materials for well-defined networks. The intention was to generate stable microcomposite dispersions with very high concentrations of polar thermally conductive fillers. Lightly crosslinked elastomeric networks with controlled amounts of polar moieties were prepared via a hydrosilation curing mechanism. High concentrations of thermally conductive micro-fillers were dispersed throughout the resins and the microcomposites were investigated as thermally conductive adhesives. Random polysiloxane copolymers containing controlled number average molecular weights (Mns) and compositions with systematically varied concentrations of hydridomethylsiloxy- or vinylmethylsiloxy- units were prepared via ring-opening equilibrations of cyclosiloxane tetramers. These precursors were functionalized with precise concentrations of polar pendent moieties via hydrosilation (nitrile) or free radical addition reactions (phosphine and carboxylic acids). Valuable additions to the family of polysiloxanes were prepared by oxidizing the phosphine moieties to form phosphine oxide containing polysiloxanes. Defined concentrations of residual hydrido- or vinyl- reactive sites were crosslinked via hydrosilation to yield elastomeric adhesives. Specific interactions between the nitrile and phosphine oxide substituted polysiloxanes and the acidic proton of chloroform were shown using 1H NMR. The magnitude of the shift for the deshielded chloroform proton increased with the degree of hydrogen bonding, and was larger for the phosphine oxide species. The polar polysiloxane resins were filled with high concentrations of thermally conductive fillers including silica-coated AlN, Al spheres, BN and Ag flake, then hydrosilated to form microcomposite networks. Microcomposite adhesive strengths, thermal properties (glass transition temperature (Tg) and high temperature stability), and thermal conductivities were studied. An unfilled polysiloxane network containing only 15 mole percent phosphine oxide exhibited a dramatic improvement (46 N/m) in adhesive strength to Al adherends relative to a control polydimethylsiloxane network (2.5 N/m). Importantly, stable polysiloxane micro-dispersions were obtained with up to 67 volume percent (86 weight percent) silica-coated AlN. TEM data confirmed the dispersion homogeneity and XPS demonstrated that the particle surfaces were well-coated with the functionalized polysiloxanes. A microcomposite comprised of 67 volume percent silica-coated AlN and a polysiloxane containing only 9 molar percent nitrile groups had a thermal conductivity of 1.42 W/mK. The glass transition temperatures of the microcomposites were controlled by the amounts of polar functional moieties on the resins and the network crosslink densities. All of the microcomposites exhibited Tgs lower than -44°C and the materials remained stable in dynamic TGA measurements to approximately 400°C in both air and nitrogen. Ph. D.