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A facile synthesis of hydroxyethyl-functionalized poly(ether sulfone) (PESu) oligomers permitted subsequent melt transesterification into segmented block copolymers with poly(butylene terephthalate). The unique solubility of the PESu oligomers in the melt with 1,4-butanediol and dimethyl terephthalate enabled a systematic study of segment length on thermomechanical properties of the resulting block copolymers. 1H NMR spectroscopy revealed a compositional dependence on the average segment length of the PBT. Additionally, the concert of NMR spectroscopy, DSC, and DMA highlighted critical segment lengths for crystallization and phase separation. In agreement with a relatively constant Tm and phase separation observed with DSC and DMA, respectively, small-angle X-ray scattering identified a compositionally independent lamellar thickness, while the amorphous layer thickness increased with PESu incorporation. As a result, the complementary analytical techniques provided an understanding of the morphological inf...

A comprehensive discussion is provided of the critical physical, chemical and structural parameters, such as soft and hard segment structures and their molecular weights, polymer composition, solubility parameters, competitive intermolecular interactions and others, which strongly affect the morphology and bulk and surface properties of segmented thermoplastic polyurethanes, polyureas and polyurethaneureas (TPUs). Important developments related to the design, synthesis and structure-property behavior of segmented polyurethanes are discussed. Although the main emphasis is placed on linear materials, some brief comments are also given on the effect of chemical crosslinking on the structure–property behavior of segmented polyurethanes.

Quantum mechanical calculations (QMC) and dissipative particle dynamics (DPD) simulations were utilized to understand the nature of the short and long-range hydrogen bonding and its influence on the microphase morphology in segmented polyurethanes and segmented polyureas prepared without chain extenders through the stoichiometric reactions of hydroxy or amine terminated poly(tetramethylene oxide) (PTMO-1000) with 1,4-phenylene diisocyanate (PPDI) and 1,3-phenylene diisocyanate (MPDI). The possibility of long-range connectivity due to a network of well-ordered hydrogen bonds between symmetrical PPDI and kinked MPDI based model urethane and urea compounds were also investigated. Special emphasis was given on the understanding of the influence of diisocyanate symmetry and nature of the hydrogen bonding between hard segments on the morphology development. QMC results obtained clearly indicated the possibility of long-range ordering of hydrogen bonds between PPDI based urethane and urea groups, while MPDI based systems did not display such a behavior. DPD results strongly supported the QMC studies and clearly demonstrated the possibility of long-range connectivity of hydrogen bonds between urethane and urea groups in PPDI based segmented copolymers, leading to the formation of microphase separated morphologies in these systems, which was not observed in the kinked MPDI based segmented urethane and urea copolymers. Computational results obtained strongly supported the experimental observations reported on the morphology and thermal and mechanical properties of these segmented polyurethanes and polyureas based on PPDI and MPDI.

Segmented polyurethanes based on polytetramethylene glycol (PTMG) of 1000 g/mol were synthesized using a two-step polymerization procedure. Various hard segments were obtained using hexamethylene diisocyanate (HDI) or 4,4′-methylenebis(phenyl isocyanate) (MDI) as the diisocyanates and hydroquinone bis(2-hydroxyethyl)ether (HQEE) or triptycene-1,4-hydroquinone bis(2-hydroxyethyl)ether (TD) as the chain extenders. The effect of rigidity and bulkiness of the hard segments on morphology, thermal and mechanical properties were studied. Fourier transform infrared (FTIR) suggested that hydrogen bonding interactions were weakened in the presence of the bulky triptycene-containing hard segments. Variable temperature FTIR demonstrated that hydrogen bonds completely dissociate at around 170 °C for polyurethanes chain extended by HQEE compared to around 110 °C for their TD analogs. Polyurethanes from MDI and TD displayed microphase mixing behavior based on atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). When HDI was used as the diisocyanate in the TD chain extended polyurethane, enhanced microphase separation was observed with comparable mechanical properties to those of the MDI analogs with HQEE.

Thermoplastic segmented polyurethanes which are based on poly(tetramethylene oxide) (PTMO) soft segment, linear symmetric para-phenylene diisocyanate (pPDI), and chain extended with 1,4-butanediol (BD) are discussed. The effect of variation of the soft and hard segment molecular weights as well as the overall hard segment content on structure–property behavior is investigated. Together, atomic force microscopy (AFM) and dynamic mechanical analysis (DMA) clearly establish the presence of a unique ordered thread-like microphase separated structure that displays considerable order. This thread-like microphase structure is similar to that of the “single molecule” hard segment systems reported earlier from our laboratory [1] , [2] , [3] , [4] . In addition, small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS) and ambient temperature tensile testing results help to better define the nature of the hard and soft domains.

A new triptycene diol (TD), triptycene-1,4-hydroquinone-bis(2-hydroxyethyl) ether, was synthesized and was used to prepare a series of copolyesters with dimethyl 1,4-cyclohexanedicarboxylate (1,4-DMCD) by melt polycondensation. Straight chain aliphatic spacers, including ethylene glycol (EG), 1,4-butanediol (BD), and 1,6-hexanediol (HD), were used as codiols with TD to explore the effects of straight chain flexible spacers on copolyester properties. A concomitant series of non-triptycene copolyesters based on hydroquinone bis(2-hydroxyethyl) ether (HBE), bis[4-(2-hydroxyethoxy)phenyl] sulfone (BHPS), 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane (BHPC), or 1,1-bis(2-hydroxyethoxy)phenyl-3,3,5-trimethylcyclohexane (BHPT) were prepared for comparison. The results demonstrated that the triptycene-containing polyesters in this study have higher thermal stability and higher glass transition temperatures (Tg’s) than the corresponding non-triptycene analogues. For triptycene-containing copolyesters, the mechanic...

Effect of polydimethylsiloxane (PDMS) soft segment molecular weight (Mn = 3200, 10,800 and 31,500 g/mol) and urea hard segment content (2.0–11.4% by weight) on the hysteresis and permanent set behavior of segmented silicone-urea (TPSU) copolymers were investigated. In spite of very low hard segment contents, all copolymers formed self-supporting films and displayed good mechanical properties. When the mechanical hysteresis and set behavior of the silicone-urea copolymers with similar hard segment contents (around 7.5% by weight) but based on PDMS-3K, PDMS-11K and PDMS-32K were compared, it was very clear that as the PDMS molecular weight increased, hysteresis and instantaneous set values decreased significantly. Copolymers based on the same silicone soft segment (PDMS-11K or PDMS-32K) but with different hard segment contents showed a linear increase in hysteresis and a slight decrease in the instantaneous set as a function of hard segment content. Constant initial stress creep experiments also showed lower creep as the PDMS segment molecular weight increased for copolymers with similar urea contents. Since the critical entanglement molecular weight (Me) of PDMS is stated to be 24,500 g/mol, our results tend to suggest important contribution of chain entanglements on the hysteresis and instantaneous set of these silicone-urea copolymers.

Novel, segmented thermoplastic silicone–urea (TPSU) copolymers based on rather high molecular weight aminopropyl terminated polydimethylsiloxane (PDMS) soft segments ( 10,800 and 31,500 g/mol), a cycloaliphatic diisocyanate (HMDI) and various diamine chain extenders were synthesized. Copolymers with very low urea hard segment contents of 1.43–14.4% by weight were prepared. In spite of very low hard segment contents, solution cast films showed very good microphase separation and displayed reasonable mechanical properties. Tensile strengths of TPSU copolymers showed a linear dependence on their urea hard segment contents, regardless of the structure of the diamine chain extender used. The modulus of silicone–urea copolymers is dependent on the urea concentration, but not on the extender type or PDMS molecular weight. When silicone–urea copolymers with identical urea hard segment contents were compared, copolymers based on PDMS-31,500 showed higher elongation at break values and ultimate tensile strengths than those based on PDMS-10,800. Since the critical entanglement molecular weight (Me) of PDMS is about 24,500 g/mol, these results suggest there is a significant contribution from soft segment chain entanglement effects in the PDMS-31,500 system regarding the tensile properties and failure mechanisms of the silicone–urea copolymers.

In our previous publication on the structure–property behavior of segmented polyurethanes based on castor oil [Petrovic ZS, Xu Y, Zhang W. Polymer Preprints 2007;48(2):852–3.], the results showed that these materials which possessed a soft segment weight concentration (SSC) of 70% have both low tensile strength and elongation at break. This behavior is distinctly different from segmented polyurethanes of comparable soft segment content obtained from petrochemical polymeric diols that possess terminal hydroxyl groups. The poor elastic properties of these segmented polyurethanes were ascribed to the low molecular weight of the polymers as well as due to the presence of the six-carbon “dangling chain”, which may influence the morphology of the resulting segmented polyurethanes. To further understand this behavior, four segmented polyurethanes with the SSC of 70, 60, 50, and 40%, respectively, were synthesized from a polyricinoleate diol with an Mn of 2580, diphenylmethane diisocyanate (MDI) and butanediol. The objective of this work was to study the effect of SSC on the morphology of the resulting polyurethanes, and to correlate the morphology with the properties of these bio-based segmented polyurethanes. Polymers were characterized by GPC, viscometry and spectroscopic methods. Thermal and mechanical properties of the polymers indicated good microphase separation. Microphase morphology was also noted by SAXS and AFM. Finally, “spherulitic-like” superstructures were noted in the solution cast films that are believed to arise from the nucleation and crystallization of the hard segments.

The effects of long-range connectivity between urea hard domains on the microphase morphology and mechanical properties of novel, segmented, non-chain extended polyureas based on single isocyanate molecules were analyzed. This was achieved by systematic disruption of the intermolecular bidentate hydrogen bonding between the urea hard segments by the incorporation of a hydrogen bond screener, LiCl. A systematic decrease in the breadth of the service temperature window and mechanical properties of the polyureas were observed in the presence of LiCl, due to the disruption of the long range connectivity between the hard segments. The above mentioned effects were also found to be dependent on the symmetry of the diisocyanate hard segments.

Segmented thermoplastic polyurethanes, polyureas and polyurethaneureas (TPU) based on a given hard segment and two chemically different soft segments display interesting microphase morphologies and thermal, mechanical and surface properties. In these systems the final TPU morphology is mainly controlled by the structure, amount and molecular weight of the soft segment oligomers and the nature and extent of specific intermolecular interactions between the mixed soft segments themselves and with the urethane hard segments. These interactions lead to variable compatibilities between the soft and hard segments resulting in interesting TPU morphologies. The proper choice of the two chemically different soft blocks provides more flexibility in controlling the extent of microphase separation, size and shape of the microphase domains and offers new possibilities for controlling the properties of TPUs. In this study coarse grained computer simulations were carried out to better understand the nature of intermolecular interactions and to elucidate the equilibrium microphase morphologies of TPUs with two different soft segments at 300 K. Model TPU systems investigated are comprised of poly(tetramethylene oxide) (PTMO) or poly(hexylethyl carbonate) (PHEC) and polydimethylsiloxane (PDMS) or polyisobutylene (PIB) soft segments with molecular weights in the range of 500-2500 g/mol. Hard segments consisted, in all cases, of diphenylmethane diisocyanate (MDI) based urethane repeat units and ranged from 25 to 50% by weight. Through coarse grained Dissipative Particle Dynamics (DPD) simulations it was demonstrated that by varying the composition and the chain lengths of the soft and hard blocks, quite different morphologies from homogeneous (or mixed) to gradient and to completely microphase separated structures were attainable. As expected, fairly hydrophobic soft blocks such as PIB and PDMS favored strong microphase separation when compared with relatively hydrophilic PHEC and PTMO segments. For comparison, morphologies of the TPUs based on single soft segments (PTMO, PHEC, PDMS and PEO) with varying molecular weights and hard segment contents were also simulated. (C) 2016 Elsevier Ltd. All rights reserved.

Raw soybean oil was hydroxylated with acetic acid and hydrogen peroxide to prepare soy-based polyols of various functionalities. These polyols were reacted with a modified diphenyl methane diisocyanate (Isonate 143L) to make polyurethane networks. The sol fractions decreased as the hydroxyl number of the polyol increased, and the glass-transition temperatures increased with the hydroxyl number, as did the rubbery plateau storage modulus and Young's modulus of the networks. When the glass-transition temperatures of each network were plotted as a function of the polyol's hydroxyl number, a linear relationship was observed over the range investigated. This trend closely matched that of our previous work with soy-based polyurethane networks. A second series of networks was prepared with the same polyols but with different isocyanates. The nature of the crosslinker was shown to somewhat influence the sol fractions, glass-transition temperatures, and stress–strain behavior of the networks. A linear relationship was recorded between the storage modulus at 125°C of a network and the average functionality of the polyol from which it was synthesized. Finally, two separate polyurethane networks were prepared through the blending of two polyols: one based on petroleum and the other based on soy. These networks were also characterized, and the compatibility of each blend was addressed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Novel, segmented non-chain extended polyureas were synthesized. Soft segments (SS) were based on poly(tetramethylene glycol) (PTMO) (average molecular weight 1000 or 2000 g/mol) and hard segments (HS) were based on a single molecule of a diisocyanate, which was either 1,6-hexamethylene diisocyanate (HDI), 1,4-phenylene diisocyanate (pPDI) or 1,4-trans-cyclohexyl diisocyanate (CHDI). An increase in the SS molecular weight was found to lead to an increased formation of SS crystallites below 0 °C, which increased the low temperature modulus. Both 1K and 2K PTMO-based polyureas showed a microphase separated morphology, where the HS formed thread-like, crystalline structures that were dispersed in the continuous SS matrix. Upon deformation, the HS were found to breakdown into distinctly smaller threads, which oriented along the direction of the strain; this effect was found to be partially reversible and time dependent. Both the 1K and 2K polyureas based on HDI HS were found to be thermally stable and potentially melt-processible.

Ionomeric polymer transducers (sometimes called “ionic polymer–metal composites,” or “IPMCs”) are a class of electroactive polymers that are able to operate as distributed electromechanical actuators and sensors. Traditionally, these transducers have been fabricated using water-swollen Nafion membranes. This work seeks to overcome the hydration dependence of these transducers by replacing water with an ionic liquid. In the current work, two ionic liquids are studied as diluents for ionomeric polymer transducers based on Nafion membranes. The two ionic liquids used are 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-Im). These two ionic liquids were chosen for their low viscosity and high conductivity. Furthermore, although many of the physical properties of the two ionic liquids are similar, the EMI-Tf ionic liquid is water miscible whereas the EMI-Im ionic liquid is hydrophobic. These important similarities and differences facilitated investigations of the interactions between the ionic liquids and the Nafion polymer. This paper examines the mechanisms of electromechanical transduction in ionic liquid-swollen transducers based on Nafion polymer membranes. Specifically, the morphology and relevant ion associations within these membranes are investigated by the use of small-angle X-ray scattering (SAXS), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. These results reveal that the ionic liquid interacts with the membrane in much the same way that water does, and that the counterions of the Nafion polymer are the primary charge carriers in the ionic liquid-swollen films. The results of these analyses are compared to the macroscopic transduction behavior in order to develop a molecular/morphological model of the charge transport mechanism responsible for electromechanical coupling in these membranes.

Novel segmented polyurethanes with hard segments based on a single diisocyanate molecule with no chain extenders were prepared by the stoichiometric reactions of poly(tetramethylene oxide)glycol ( M n =1000 g/mol) (PTMO-1000) and 1,4-phenylene diisocyanate (PPDI), trans -1,4-cyclohexyl diisocyanate (CHDI), bis(4-isocyanatocyclohexyl)methane (HMDI) and bis(4-isocyanatophenyl)methane (MDI). Time dependent microphase separation and morphology development in these polyurethanes were studied at room temperature using transmission FTIR spectroscopy. Solvent cast films on KBr discs were annealed at 100 °C for 15 s and microphase separation due to self organization of urethane hard segments was followed by FTIR spectroscopy, monitoring the change in the relative intensities of free and hydrogen-bonded carbonyl (C O) peaks. Depending on the structure of the diisocyanate used, while the intensity of free C O peaks around 1720–1730 cm −1 decreased, the intensity of H-bonded C O peaks around 1670–1690 cm −1 , which were not present in the original samples, increased with time and reached saturation in periods ranging up to 5 days. Structure of the diisocyanate had a dramatic effect on the kinetics of the process and the amount of hard segment phase separation. While PPDI and CHDI based polyurethanes showed self-organization and formation of well ordered hard segments, interestingly no change in the carbonyl region or no phase separation was observed for MDI and HMDI based polyurethanes. Quantitative information regarding the relative amounts of non-hydrogen bonded, loosely hydrogen bonded and strongly hydrogen bonded and ordered urethane hard segments were obtained by the deconvolution of C O region and analysis of the relative absorbances in C O region.

The effect of time and temperature on the air oxidation of soybean oil in the absence of catalysts or added initiators was investigated. It was possible to divide the air oxidation of soybean oil into three regimes. The first regime of air oxidation resulted in insignificant change in the hydroxyl number. During this regime, it was proposed that natural antioxidants, which are present in raw soybean oil, were consumed and peroxide formation occurred. A drastic increase in hydroxyl number due to the formation and subsequent decomposition of peroxides marked the second regime of air oxidation. In the third regime of air oxidation, free radical crosslinking of the soybean oil occurred, and an insoluble gel was formed. The three regimes of air oxidation were used as a guide for the preparation of soy-based polyols and crosslinked polymers. Crosslinked, tack-free coatings were prepared from a metal catalyzed oxidation of soybean oil, where soybean oil and ambient oxygen were the only reactants. Higher temperatures (125°C) were more efficient than lower (50°C) for obtaining high gel fractions and tack-free coatings. Cure of the coatings was expedited with exposure of the coating to UV irradiation after initial heating. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 690–697, 2006

Polyurethane Networks (PUNs) were synthesized using polyols derived from soybean oil, petroleum, or a blend of the two in conjunction with diisocyanate. The soybean-based polyols (SBPs) were prepared using air oxidation, or by hydroxylating epoxidized soybean oil. Some of the networks were subjected to several solvents to determine their respective swelling behavior and solubility parameters. Sol-fractions were also determined, and DMA experiments were utilized to monitor the changes in storage modulus and tan δ with temperature for networks with sol and with the sol extracted. A linear relationship was noted between the hydroxyl number of a SBP and the glass transition temperature of its corresponding unextracted PU network within the range of hydroxyl numbers (i.e., 55–237 mg KOH/g) and glass transition temperatures (i.e., −21–+83°C) encountered in this work. This same linear relationship was realized between the weighted hydroxyl number of soy and petroleum-based polyol blends and the glass transition temperature of the resulting unextracted and extracted network PUs within the ranges utilized in this study (i.e., 44–57 mg KOH/g, −54–19°C). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1432–1443, 2006

Novel segmented polyurethaneurea copolymers were synthesized using a poly(ethylene–butylene) glycol based soft segment and either hydrogenated diphenyl methane diisocyanate (HMDI) or hexamethylene diisocyanate (HDI) in addition to either ethylene diamine (EDA) or 2-methyl-1,5-diaminopentane (DY) as the chain extender. Dynamic mechanical analysis (DMA), small angle X-ray scattering (SAXS) and in some cases atomic force microscopy (AFM) established the presence of a microphase-separated structure in which hard microdomains are dispersed throughout a soft segment matrix. Wide angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) imply that the materials are amorphous. Samples that are made with HMDI/DY and have hard segment contents in the range of 16–23 wt% surprisingly exhibit near-linear mechanical deformation behavior in excess of 600% elongation. They also show very high levels of recoverability even though their hysteresis is also considerable. The materials have all proven to be melt processable in addition to solution processable.

The solid-state structure–property behavior of highly branched segmented poly(urethane urea) (PUU) copolymers and their linear analog was investigated. A limited study of their solution rheological behavior was also undertaken. The linear PUUs were synthesized by the two-step prepolymer method, whereas the oligomeric A2+B3 methodology was utilized to synthesize the highly branched materials. The soft segments (SS) were either poly(tetramethylene oxide) (PTMO) or poly(propylene oxide) (PPO). All copolymers utilized in this study, with one exception, contained 28 wt% hard segment (HS) content. DMA, SAXS, and AFM studies indicated that the linear as well as the highly branched PUUs were microphase separated. The SS Tg of the highly branched PUUs was nearly identical to that of their respective linear analogs. However, the linear copolymers exhibited broader and less temperature sensitive rubbery plateaus, both attributed to one or both of two reasons. The first is better hydrogen bonding organization of the HS phase as well as greater HS lengths than in the highly branched analogs. The second parameter is that of a potentially higher chain entanglement for the linear systems relative to the branched analogs. Tapping-mode AFM phase images confirmed the microphase morphology indicated by SAXS and DMA. Ambient temperature strain-induced crystallization was observed in the PUU based on PTMO 2040 g/mol at a uniaxial strain of ca. 400%, irrespective of the chain architecture. Stress–strain, stress relaxation, and mechanical hysteresis of the highly branched copolymers were in general slightly poorer than that of their linear analogs. Ambient temperature solution viscosity of the highly branched materials in dimethyl formamide was substantially lower that that of the linear samples of nearly equal molecular weight.

The time-dependent morphology development in a segmented polyurethane, which was prepared by the reaction of equimolar amounts of 1,4-phenylene diisocyanate (pPDI) and poly(tetramethylene oxide)glycol of 〈Mn〉 of 975 g/mol, was investigated. No chain extender was utilized during the synthesis, and the resultant monodisperse hard segments constituted 14 wt % of the copolymer. Time-dependent microphase separation and morphology development was studied at room temperature by using solvent-cast films which were heated above the hard segment melting temperature, 55 °C, to erase the semicrystalline microphase morphology. Atomic force microscopy showed that, following heat treatment, the hard phase first developed into short rods within 30 min, followed by a growth period during which the short rods grew longer and eventually into a well-defined percolated structure. Morphology development was also followed by FTIR spectroscopy. While the intensity of the free CO peak at 1730 cm-1 decreased, the intensity of the ...

Poly(propylene oxide) (PPO) was incorporated in a controlled manner between poly(dimethylsiloxane) (PDMS) and urea segments in segmented polyurea copolymers and their solid state structure–property behavior was investigated. The copolymers contained PDMS segments of MW 3200 or 7000 g/mol and an overall hard segment content of 10–35 wt%. PPO segments of MW 450 or 2000 g/mol were utilized. Equivalent polyurea copolymers based on only PDMS as the soft segment (SS) component were used as controls. The materials (with or without PPO) utilized in this study were able to develop microphase morphology as determined from dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS). DMA and SAXS results suggested that the ability of the PPO segments to hydrogen bond with the urea segments results in a limited inter-segmental mixing which leads to the formation of a gradient interphase, especially in the PPO-2000 co-SS containing copolymers. DMA also demonstrated that the polyureas based on only PDMS as the SS possessed remarkably broad and nearly temperature insensitive rubbery plateaus that extended up to ca. 175 °C, the upper temperature limit depending upon the PDMS MW. However, the incorporation of PPO resulted in more temperature sensitive rubbery plateaus. A distinct improvement in the Young's modulus, tensile strength, and elongation at break in the PPO-2000 and PDMS-7000 containing copolymers was observed due to inter-segmental hydrogen bonding and the formation of a gradient interphase. However, when PPO was incorporated as the co-SS, the extent of stress relaxation and mechanical hysteresis of the copolymers increased relative to the segmented polyureas based on the utilization of only PDMS as the soft segment component.

Three nearly identical linear low density polyethylene resins based on copolymers of ethylene with 1-butene (B), 1-hexene (H) and 1-octene (O) were utilized to investigate the effect of short chain branch length on the mechanical properties of blown and compression molded (quenched and slow cooled) films. The content of short chain comononer in the three copolymers was ca. 2.5–2.9 mol% that corresponded to a density of 0.917–0.918 g/cm 3 . Within a given series, the tensile properties of these films do not show any significant difference at slow deformation rates (up to 510 mm/min), even though the DSC and TREF profiles of ‘H’ and ‘O’ differed slightly in comparison to ‘B’. However, at higher deformation rates (ca. 1 m/s), the breaking strength of these films was found to increase with increasing short chain branch length. In addition, the Spencer impact and Elmendorf tear strength of the blown films were also observed to increase with increasing short chain branch length. Further, dart impact strength and high-speed puncture resistance (5.1 m/s) of 1-octene and 1-hexene based samples was also observed to be higher than that based on 1-butene. The blown films displayed low and comparable levels of equivalent in-plane birefringence and crystalline orientation by wide angle X-ray scattering. This confirms that the differences in mechanical properties in the blown film series are not attributable to differences in molecular orientation. The deformation behavior of both the compression molded and blown films were also investigated in a well-defined controlled regime by analyzing their essential work of fracture. It was found that the essential work of fracture of films based on 1-hexene and 1-octene was higher than that of films based on 1-butene. While the origin of these differences in mechanical properties with increasing short chain branch length is not fully understood, the present investigation confirms this effect to be pronounced at high deformation rates for both the blown and compression molded quenched films.

Thermoplastic segmented polyurethane and polyurea copolymers whose monodisperse hard segments are based on only a single diisocyanate molecule are discussed. The solid-state structure-property behavior of these materials demonstrates that a proper selection of the level of symmetry and/or cohesiveness of the hard microdomains may allow elimination of the traditional requirement of chain extension to obtain melt processable segmented urethanes, and more specifically, urea copolymers with useful structural properties.

Many polyurethane elastomers display excellent mechanical properties and adequate biocompatibility. However, many medical-grade polyurethanes are prepared from aromatic diisocyanates and can degrade in vivo to carcinogenic aromatic diamines, although the question of whether the concentrations of these harmful degradation products attain physiologically relevant levels is currently unresolved and strongly debated. It is therefore desirable to synthesize new medical-grade polyurethanes from less toxic aliphatic diisocyanates. In this paper, biocompatible segmented polyurethane elastomers were synthesized from aliphatic diisocyanates (1,4-diisocyanatobutane (BDI) and lysine methyl ester diisocyanate (LDI)), novel diurea diol chain extenders based on tyrosine and tyramine, and a model poly(ethylene glycol) (PEG) diol soft segment. The objectives were to design a hard segment similar in structure to that of MDI-based polyurethanes and also investigate the effects of systematic changes in structure on mechanical and biological properties. The non-branched, symmetric polyurethane prepared from BDI and a tyramine-based chain extender had the highest modulus at 37 degrees C. Introduction of symmetric short-chain branches (SCBs) incorporated in the tyrosine-based chain extender lowered the modulus by an order of magnitude. Polyurethanes prepared from LDI were soft polymers that had a still lower modulus due to the asymmetric SCBs that hindered hard segment packing. Polyurethanes prepared from tyramine and tyrosine chain extenders thermally degraded at temperatures ranging from 110 to 150 degrees C, which are lower than that reported previously for phenyl urethanes. All four polyurethanes supported the attachment, proliferation, and high viability of MG-63 human osteoblast-like cells in vitro. Therefore, the non-cytotoxic chemistry of these polyurethanes make them good candidates for further development as biomedical implants.

A series of seven linear homopolymers of poly(methylmethacrylate) ranging from 12,470 to 365,700 g/mol M w , were utilized to further explore scaling relationships between viscosity and concentration in a good solvent at 25 °C and to investigate the impact of these relationships on fiber formation during electrospinning. For each of the polymers investigated, chain dimensions (hydrodynamic radius and radius of gyration) were measured by dynamic light scattering to determine the critical chain overlap concentration, c * . The experimentally determined c * , was found to be in good agreement with the theoretically determined value that was calculated by the criteria c * ∼1/[ η ], where the intrinsic viscosity was estimated from the Mark–Houwink parameters, K and a (at 25 °C in dimethyl formamide) obtained from the literature. The plot of the zero shear viscosity vs. c / c * distinctly separated into different solution regimes, viz. dilute ( c / c * c / c * c / c * >3). The crossover between semidilute unentangled and semidilute entangled regimes in the present investigation occurred at c / c * ∼3, which, therefore, marked the onset of the critical chain entanglement concentration, c e , according to the procedure utilized by Colby and co-workers [Colby RH, Rubinstein M, Daoud M. J de Phys II 1994;4(8):1299–310. [52] ]. Electrospinning of all solutions was carried out at identical conditions to ascertain the effects of solution concentration, molecular weight, molecular weight distribution and viscosity on fiber formation and morphological features of the electrospun material. Only polymer droplets were observed to form from electrospinning of solutions in the dilute concentration regime due to insufficient chain overlap. As the concentration was increased, droplets and beaded fibers were observed in the semidilute unentangled regime; and beaded as well as uniform fibers were observed in the semidilute entangled regime. Uniform fiber formation was observed at c / c * ∼6 for all the narrow MWD polymers ( M w of 12,470–205,800 g/mol) but for the relatively broad MWD polymers ( M w of 34,070 and 95,800 g/mol), uniform fibers were not formed until higher concentrations, c / c * ∼10, were utilized. Dependence of fiber diameter on concentration and viscosity was also determined, viz. fiber dia∼( c / c * ) 3.1 and fiber dia ∼ η 0 0.71 respectively. These scaling relationships were in general agreement with that observed by Mckee et al. [McKee MG, Wilkes GL, Colby RH, Long TE. Macromolecules 2004;37(5):1760–67. [33] ].

Soluble model segmented poly(urethane urea)s (PUU) with or without hard segment (HS) branching were utilized to explore the importance of hydrogen bonding and chain architecture in mediating the long-range connectivity of the HS phase. The HS content of all the PUU copolymers was 22 wt %, and the soft segment (MW 970 g/mol) was a heterofed random copolymer of 50:50 ethylene oxide:propylene oxide, which possesses a single terminal hydroxyl group (monol). An 80:20 isomeric mixture of 2,4- and 2,6-toluene diisocyanate, 4,4',4''-triphenylmethane triisocyanate and water were utilized during the chain extension step of the synthesis to incorporate HS branching. DSC and SAXS results on the final plaques indicated that the samples were still able to establish a microphase morphology even in the presence of the highest extent of HS branching utilized in the study. The tapping-mode AFM phase image of the PUU sample without HS branching exhibited the presence of long ribbonlike hard domains that percolated through the soft matrix. The long-range connectivity of the HS was increasingly disrupted with higher levels of HS branching. Accompanying such disruption was a systematic mechanical softening of the PUU samples. FT-IR indicated that incorporation of HS branching disrupted the hydrogen-bonded network within the hard phase. These results demonstrate the importance of hydrogen bonding and chain architecture in mediating the long-range connectivity and percolation of the HS and achieving dimensional stability.

A novel methodology for in situ cross-linking of polymeric fibers during electrospinning is described. The electrospinning apparatus was modified to facilitate UV irradiation of the electrospun fibers while in flight to the collector target. Three polymers with different mol % of the photoreactive cinnamate functional group (4, 9, and 13 mol %) were synthesized and utilized for this study. Fibers of cinnamate functionalized poly(methyl methacrylate-co-2-hydroxyethyl acrylate) were cross-linked in situ by UV irradiation during electrospinning. Subsequent FTIR measurements on irradiated and nonirradiated electrospun fibers indicated both [2π + 2π] cycloaddition of the vinylene CC and trans−cis photoisomerization of the cinnamate group. Furthermore, the irradiated copolymers were observed to form insoluble gels which indicated that the photodimerization was the primary photoprocess during UV irradiation, leading to the formation of a cross-linked network. As expected, it was found that the gel fraction incre...

The effect of the variables of polydimethylsiloxane (PDMS) soft segment (SS) length, hard segment (HS) type and content as well as choice of chain extender (its MW and symmetry) on the morphology of segmented polyurethane and polyurea copolymers was investigated. The methods of dynamic mechanic analysis, small angle X-ray scattering, atomic force microscopy, and mechanical testing were used in this analysis. Average PDMS MW of 900, 2500 or 7000 g/mol were utilized and the hard segment content ranged from 16 to 50 wt%. HMDI was used as the diisocyanate. All copolymers were synthesized via the prepolymer method. The PDMS MW had a marked effect on the morphology of the materials. Copolymers with PDMS MW of 2500 and 7000 g/mol were clearly found to be well microphase separated relative to those containing the 900 g/mol PDMS SS. The polyurea sample with a PDMS MW of 7000 and HS content of 25 wt% exhibited a remarkable service temperature window (for rubber-like behavior) of ca. 230 °C (from −55 to 175 °C) whereas it was ca. 200 °C wide (from −55 to 145 °C) for the equivalent polyurethane sample. In general, the degree of microphase separation was found to be greater in the polyurea samples due to their more cohesive bidentate hydrogen bonding.

The influence of the extent of hydrogen bonding in mediating the long-range connectivity and percolation of the hard segment phase in model tri-segment oligomeric polyurethanes (PU) was explored by using LiCl as a molecular probe. A 22 wt% hard segment containing model PU plaque based on a mono-functional oligomeric polyether, 80:20 2,4:2,6 isomeric mixture of toluene diisocyanate, and water as a chain extender was employed. Samples cast from 20 wt% solutions in dimethyl acetamide were utilized. The tapping-mode atomic force microscopy (AFM) phase image of the solution cast film sample (soft segment Tg −63 °C) without LiCl exhibited the presence of long interconnected ribbon-like hard domains. The long-range connectivity and percolation of the hard phase that arose during plaque formation gave rise to a brittle rigid solid. A systematic break-up of the hard domains was also observed by AFM when the concentration of LiCl was increased from 0.1 to 1.5 wt%. DSC analysis indicated that the samples were able, however, to maintain a microphase separated morphology even at the highest LiCl concentration utilized in the study. FT-IR data confirmed that LiCl interacts with the hard domains of the model PU samples by disrupting the hydrogen bonding capability of the urea hard segments. A systematic softening of the samples was observed with increasing LiCl content as confirmed by thermomechanical analysis. Thus, this study indicates that hydrogen bonding plays an important role in assisting the hard segments in PU to develop long-range connectivity and percolation of this phase through the soft matrix.

Five different poly(vinylidene fluoride) (PVDF) resins spanning the molecular weights from 85,000–250,000 g/mol with nearly comparable polydispersities of ca. 2.0 were investigated with respect to their strain induced crystalline morphologies as produced by a tubular uniaxial film extrusion process. By holding the process time window constant through the use of fixed melt temperature, line speed, quench height and film thickness, it was noted that as molecular weight increased, the uniaxial films produced systematically change from nearly a spherulitic structure to that of an extremely high concentration of fibril nuclei with minimal growth of folded chain lamella developing perpendicular to the fibrils. The systematic variation in the morphology was directly coupled through consideration of the melt process time window in conjunction with the characteristic relaxation time of a given resin at a given temperature. The latter was determined through use of a Carreau–Yasuda analysis of the melt rheological behavior of each resin and this relaxation time, when correlated to the process time, produced a relative Deborah number. It was distinctly shown that when the Deborah number was considerably less than unity, little crystal orientation was observed in the morphological texture whereas in the range of unity, a distinct rise in crystalline orientation occurred leading to fibril nucleation with lamella side growth in the form of the well known row structure morphology. Exceeding a Deborah number of unity led to nearly full crystalline orientation saturation and to a very high concentration of fibril nucleai with relatively few orthogonal lamella observable. The morphological textures were investigated using AFM, WAXS, SALS, SAXS and birefringence. Use of thermal analysis to determine some of the polymorphic character of the PVDF crystal form was also undertaken.

The implications of the entanglement concentration (Ce) on the electrospinning process for a series of linear and branched poly(ethylene terephthalate-co-ethylene isophthalate) (PET-co-PEI) copolymers with weight-average molecular weights (Mw) ranging from 11 700 to 106 000 g/mol and branching index values (g‘) from 1.0 to 0.43 were investigated. Analyzing the dependence of specific viscosity (ηsp) on concentration enabled the determination of the semidilute unentangled, semidilute entangled, and concentrated regimes for the PET-co-PEI solutions. Linear and branched copolymers were electrospun from semidilute unentangled, semidilute entangled, and concentrated solutions under identical conditions to determine the effects of concentration regime and molecular topology on electrospun fiber morphology. The dependence of the fiber diameter and morphology on the zero shear rate viscosity (η0) and normalized concentration (C/Ce) was determined. For copolyesters with molecular weights well above the entanglement...

Low molecular weight model trisegmented polyurethanes based on monofunctional polyols, or ‘monols’, with water-extended toluene diisocyanate (TDI) based hard segments (HS) are investigated. The formulations of the materials generated are similar to those of flexible polyurethane foams with the exceptions that the conventional polyol is substituted by an oligomeric monofunctional polyether of ca. 1000 g/mol molecular weight; and no surfactant is utilized. Plaques formed from these model systems are shown to be solid materials at ambient even at their relatively low molecular weights of 3000 g/mol and less. SAXS, DSC, and AFM are utilized to investigate the microphase separated morphologies of the samples generated. WAXS results show that the local packing of the HS is of a similar nature as that in actual flexible polyurethane foams. AFM phase images, for the first time, reveal the ability of the HS to self-assemble through bidentate hydrogen bonding and form lath-like percolated structures, resulting in solid plaques, even though the overall volume of the system is well dominated by the two terminal liquid-like polyether segments.

Epoxidized soybean oil was effectively converted to carbonated soybean oil (CSBO) containing five-membered cyclic carbonates by reaction with carbon dioxide in the presence of tetrabutylammonium bromide as catalyst at 110°C in high yield. CSBO could easily react with di- or tri- primary amines to give the corresponding nonisocyanate polyurethane networks (NIPUs). A model reaction between CSBO and n-butylamine showed the effective ring opening of five-membered cyclic carbonate moieties in the triglyceride molecules by the amine to form β-hydroxyurethane systems. NIPUs were further characterized by the three techniques of solvent extraction, dynamical mechanical analysis, and limited tensile testing. The data from these methods confirmed the network character of all materials and also showed how the levels of extractables, Tg, and mechanical properties varied with type of amine and, in the case of ethylenediamine, the effect of stoichiometry. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 883–891, 2004

Approximately 30 years after their preparation, the nanoscale morphology of a series of ‘model’ segmented polyurethane elastomers has been further elucidated using the technique of tapping mode AFM. The materials investigated are based on 1,4-butanediol extended piperazine based hard segments and employ poly(tetramethylene oxide) soft segments. The chemistry of these polyurethanes was specifically controlled in a manner which yielded monodisperse hard segments precisely containing either one, two, three, or four repeating units. Phase images obtained via AFM, for the first time, enable visual representation of the microphase separated morphology of these materials. AFM images also confirmed the presence of a spherulitic morphology, as shown several years ago using SALS and SEM. In addition, applying AFM to films of freshly prepared solution cast samples, the observed lath-like hard domains are suggested to preferentially orient with their long axis along the radial direction of the spherulites, while the respective crystalline hard segments comprising the hard domains are, in turn, preferentially oriented perpendicular to the spherulitic radius. The hard domain connectivity was found to increase with increasing percentage hard segment content of the polymers.

Simultaneous electrospinning of two polymer solutions in a side-by-side fashion is conducted for two bicomponent polymer systems—poly (vinyl chloride)/segmented polyurethane (PVC/Estane®) and poly(vinyl chloride)/poly(vinylidiene fluoride) (PVC/PVDF). The new experimental device is described and suitable process conditions to electrospin bicomponent fibers are described. Field emission scanning electron microscopy and energy dispersive spectroscopy were utilized to interpret the results regarding local structure and chemical composition, respectively.

A series of blown films were prepared using two high density polyethylene resins of differing molecular weight and molecular weight distribution, using a high stalk process. Both the resins were processed at three frost line heights (FLHs) and three draw down ratios to determine the effect of processing parameters and resin characteristics on final film morphology and mechanical properties. By changing the FLH and the time to initiate transverse direction (TD) expansion, the relative number of lamellae stacked both perpendicular and parallel to the machine direction (MD) could be controlled for a constant blow up ratio (BUR) of 4:1. It was determined that the proportion of lamellae stacked parallel to the MD increased with increasing FLH. This effect was found to be related to the relaxation behavior of the melt and bubble shape. Increasing the stress in the stalk region was observed to lead to a reduction in stalk diameter just prior to bubble expansion, resulting in a greater effective BUR. Film morphology was observed to strongly influence end mechanical properties. Elmendorf tear resistance was found to increase in the MD and decreased in the TD with increasing FLH. The dart impact strength of these films was characterized with the surprising result that for one of the two resins studied, the dart impact increased with decreasing film gauge.

The effects of methyl acrylate (MA) incorporation (0–15 mol%) on the glass transition, melting behavior, and the peak temperature of the stabilization exotherm in acrylonitrile (AN) based copolymers were studied. A qualitative decrease in crystalline content with increasing MA content was observed using wide angle X-ray scattering (WAXS). The lower crystallinity of the high MA content copolymers could also be noted by the magnitudes of the modulus drop at Tg using dynamic mechanical analysis (DMA) and the step change in heat capacity at Tg using differential scanning calorimetry (DSC). The DSC and differential thermal analysis (DTA) results indicated that the melting temperature of the copolymers decreased with increasing MA content. The magnitude of the crystallization exotherms decreased with successive melting/crystallization cycles. DTA experiments demonstrated that the stabilization reaction, which transforms polyacyrlonitrile into an insoluble, rigid structure, is delayed by the presence of the comonomer.

In continuing efforts to understand urea phase connectivity in flexible polyurethane foams and its implications on physical properties, LiCl is used to alter the phase-separation behavior of slabstock foams. Comparisons are also drawn with plaque counterparts, which are prepared using the same polyol, isocyanate, and chain extender (water). LiCl is shown to alter the solid-state phase separation behavior of the foams and the plaques in a similar manner. This is confirmed using multiple characterization techniques, which provide information at different scale lengths. The foams and plaques with and without LiCl are shown to possess a microphase separated morphology with interdomain spacings of ca. 100 A. SAXS and TEM reveal that addition of LiCl reduces the urea aggregation behavior, typical in slabstock polyurethane foams, leading to a loss in the urea phase macro connectivity. Hard segment ordering, as studied by WAXS and FTIR, is shown to be of a similar nature in the plaque and foam, which do not incorporate LiCl. Addition of LiCl leads to a loss in the segmental packing behavior, or micro level connectivity of the urea phase, in both the plaques and corresponding foams, as inferred from WAXS and FTIR. The LiCl additive interacts with the polyol soft segments in an insignificant manner as shown from FTIR and DMA. In addition, foams containing LiCl are found to possess more intact cell windows due to the influence of LiCl on reaction kinetics as well as its effect on the precipitation of the urea phase. The experimental observations are supported by quantum mechanical calculations using a density functional theory approach, where molecular interactions between LiCl and model ether, urethane, and urea compounds are investigated. Interaction geometries of most stable complexes and their stability energies are calculated. Stability energies of ether/LiCl, urethane/LiCl, and urea/LiCl were determined to be −189, −617, and −687 kJ/mol, respectively, reinforcing that LiCl interacts predominantly with urea hard segments and in a minimal manner with the polyol soft segments.

The solid state structure–property behavior was investigated of a series of poly(ether- block -amide) PEBAX ® thermoplastic elastomers based on nylon 12 and poly(tetramethylene oxide) with varying hard segment content. Particular emphasis was placed on better defining the morphological features of this entire series of commercially available materials. Compression molded and solution cast samples were studied by the techniques of DMA, DSC, WAXS, SAXS, AFM, SALS and stress–strain response. The strain-induced crystallization behavior of the soft polyether (PE) segments was also investigated. All samples exhibited a microphase separated morphology over a broad temperature range. As expected, an increase in the interconnectivity of the polyamide hard phase was greatly controlled by the polyamide (PA) content. Due to the crystallization of the PA hard segment, the formation of PA lamellar crystals was noted in both melt and solution cast films. At the higher PA contents, a distinct spherulitic superstructure was also observed but this form of morphological texture was diminished as the PE soft segment content increased. Limited studies of the deformation/recovery behavior of the spherulitic superstructure provided further information concerning the interaction between the hard and soft segments.

Segmented poly(urethane–urea)s have been synthesized with mixed soft segments of ultra-low monol content poly(propylene glycol) (PPG) and tri(propylene glycol) (TPG) which allows the fabrication of quality elastomers without crosslinking. The narrow molecular weight distribution of the ultra-low monol content PPG polyols allows for the probing of the influence of the low molecular components of the molecular weight distribution through the inclusion of low molecular homologs of PPG such as TPG. Structure–property relationships for these materials were investigated as average soft segment molecular weight was varied by blending 8000 g/mol PPG with TPG to achieve molecular weights of 2500, 2000, and 1500 g/mol. Morphological features such as microphase separation, interdomain spacing and interphase thickness were quantified and revealed with SAXS. AFM was utilized to verify the microphase separation characteristics inferred by SAXS. The thermal and mechanical behavior was assessed through applications of DMA, DSC, and conventional mechanical tests. It was found that as the average soft segment molecular weight was decreased through the addition of TPG, the interdomain spacing distinctly increased contrary to the trend seen for decreasing soft segment molecular weight in PPG based systems without TPG. Additionally, the inclusion of TPG in the poly(urethane–urea) formulations resulted in the formation of larger hard domains as evidenced by AFM. These results and supporting evidence from DMA, DSC, birefringence, and mechanical testing led to the conclusion that TPG apparently acts more as a chain extender as well as, or in contrast to, a soft segment.

Urea phase connectivity has been probed by systematically varying the hard segment content, and lithium chloride content, in a series of plaques based on slabstock flexible polyurethane foams. The plaque formulations are identical to those of slabstock polyurethane foams with the exception that a surfactant is not utilized. Small angle X-ray scattering (SAXS) is used to demonstrate that all materials investigated are microphase separated with similar interdomain spacings, irrespective of hard segment content (21–37 wt%) or LiCl content. Several complimentary characterization techniques are employed to reveal that urea phase connectivity is present at different length scales. Macrolevel connectivity, or connectivity of the large-scale urea rich aggregates typically observed in flexible slabstock polyurethane foams, is probed using SAXS, TEM, and atomic force microscopy. These techniques collectively show that the urea aggregation increases as the hard segment content is increased. Incorporation of LiCl is shown to systematically reduce the urea aggregation behavior, thus leading to a loss in the macroconnectivity of the urea phase. Wide angle X-ray scattering is used to probe the regularity in segmental packing, or the microlevel connectivity between the hard segments, which is observed to decrease systematically on addition of LiCl. The loss in microlevel connectivity is suggested to increase chain slippage, and leads to increased rates of stress-relaxation for the samples containing LiCl. Materials containing LiCl also display relatively short rubbery plateaus as compared to their counterparts which do not contain the additive. Modulus values, as obtained at ambient conditions by stress-strain analyses, are found to be a stronger function of LiCl content when the hard segment content is higher.

Statistical (random) copolymers of acrylonitrile (AN) and methyl acrylate (MA) have been synthesized by free radical homogeneous (solution) and heterogeneous (suspension) methods. Selected compositions can be fabricated by environment friendly, solvent-free melt spinning and are of interest as precursors for carbon fibers. The dynamic and steady state melt viscosities of these copolymers were studied as a function of molecular weight and copolymer composition. Melt processability at 200–220 °C depends on the copolymer composition, and also on the molecular weight, which was controlled by chain transfer agent concentration and reaction temperature. Copolymers of controlled molecular weight containing 10 or more mol[percnt] of methyl acrylate show good melt processability, which can be further enhanced by stabilizers. This thermoplastic behavior is supported by a significant increase in temperature by the cyclization exotherm. Thermal analysis (differential scanning calorimetry, dynamic mechanical analysis) further illustrates that the comonomers retarded the cyclization, which permits thermoplastic processing.

Scanning transmission X-ray microscopy (STXM) and atomic force microscopy have been used to study the morphology and chemical composition of macrophase-segregated block copolymers in plaque formulations based on water-blown flexible polyurethane foams. Although there has been a large body of indirect evidence indicating that the observed macrophase-segregated features in water-rich polyurethane foams are due principally to urea components, this work provides the first direct, spatially resolved spectroscopic proof to support this hypothesis. The STXM results are consistent with a segregation model where urea segments segregate, forming enriched phases with the majority of the polyether- polyol and urethane groups at the chain ends of the urea hard segments. Chemical mapping of the urea, urethane, and polyether distribution about the urea-rich segregated phases showed that the urea concentration changes gradually (across several hundred nanometers) in a butylene oxide-based foam. This mapping also showed the urea-rich segregated phases present as a partial network in an ethylene oxide/propylene oxide sample.

Polyacrylonitrile (PAN) terpolymers consisting of acrylonitrile/methyl acrylate (AN/MA) systems with added amounts of a termonomer (acid based) were synthesized in an effort to generate melt spinnable carbon fiber precursors. The complex viscosity was measured as a function of time in the temperature range of 200–220 °C, and was found to be dependent on both, the amount, as well as the nature of the termonomer. For the different acid termonomers studied, the cyclization/crosslinking reactions occurring during stabilization as evidenced by the increase in viscosity over time of the PAN system ranged in the order, itaconic acid>acrylamide>methyl acrylic acid>acrylic acid (IA>AM>MAA>AA). Dynamic shear experiments indicated that an AN/MA system containing 3 mol% IA seemed well suited for melt spinning and stabilization. A chemorheological correlation was used to describe the viscosity variation in the PAN system as a function of IA content, temperature and time.

Liquid crystalline polyesters based on hexanediol, dimethyl 4,4′-biphenyldicarboxylate, and various levels of dimethyl 5-sodiosulfoisophthalate (0–20 mol%) were prepared using a conventional melt polymerization process. The presence and quantification of the ionic functionality was surveyed using 1H NMR spectroscopy. Solution viscosities and corresponding molecular weights decreased when the ionic monomer concentration exceeded a critical value (higher than 3 mol%). Differential scanning calorimetry indicated a maximum in the isotropic transition temperature versus ionic modification at approximately 10 mol%. Dynamic mechanical analysis indicated that the glass transition temperature was suppressed due to ionic association at high concentrations (greater than 3 mol%) of ionic functionality. Polarized light microscopy and wide-angle X-ray diffraction were used to identify the smectic liquid crystalline and crystalline phases. © 2002 Society of Chemical Industry

We discuss here the first two stages of the tenter-frame film manufacturing process for HDPE, viz. (a) the extrusion of the polymer onto a cooled cast roll (base sheet) and (b) drawing along the machine direction (MD) using several sets of rolls (referred to as machine draw orientation (MDO) sheet). The structure–property relationships are analyzed for a single resin when the cast-roll temperature, MDO temperature and MD draw ratio are systematically varied. The thick base sheets were made by extrusion onto a cast roll at three different temperatures of Tb, Tb−11°C and Tb+11°C (Tb being a reference temperature for the base-sheet draw). While the WAXD indicated an unoriented system, atomic force microscopy (AFM) and transmission electron microscopy (TEM) revealed spherulites of ca. 3–5 μm diameter across the thickness of this base sheet. DSC indicated that the base sheet possessed a broad distribution of lamellar thickness and had a degree of crystallinity (Xc) of ca. 75%. After drawing 6X along the MD at three different drawing temperatures, of TMDO, TMDO−8°C and TMDO+8°C (TMDO being a reference temperature for the MDO-sheet draw), both AFM and TEM revealed a complete change in morphology to well-developed lamellar stacks oriented perpendicular to the MD. The MD draw ratio was then systematically varied from 1.5X, 2.25X, 3X, 4.5X to 6X, while keeping the other processing variables constant to understand how transformation of the spherulites to a stacked lamellar morphology took place. A very systematic change in morphology and orientation of the MDO sheet was observed with changing draw ratios, while the degree of crystallinity did not change. For the conditions utilized, the draw ratio of 2.25X was enough to destroy the general features of the bulk spherulitic superstructure although the broken and deformed lamellar remnants of the spherulites remained. With higher draw ratios, well-stacked lamellar structures oriented perpendicular to MD were gradually introduced at the expense of the deformed lamellae. At a draw ratio of 6X, only stacked lamellar structures were present. We discuss the causes of this transformation from primarily three standpoints: (a) localized melting and recrystallization followed by microfibrillation, (b) bulk melting followed by row nucleation and (c) a combination of the above two mechanisms. Interestingly, both X-ray and refractive index measurements revealed that the MDO process resulted in some level of biaxial orientation of the crystal phase. This arises due to the nature of the MDO process, which places constraints on the narrowing of the transverse dimensions during drawing.

This study introduces a novel high-temperature semicrystalline polyimide, which is based on an ether diamine (TPER or 1,3(4)APB) and BTDA dianhydride, both being commercially available. Phthalic anhydride is used as an endcap for improving thermal stability. The polyimide displays a Tg at ca. 230°C and two prominent melting endotherms at 360 and 416°C, respectively, with a sharp recrystallization exotherm following the lower melting endotherm. Significant recrystallization ability from the melt (at 450°C for 1 min) is observed with cooling rates faster than 200°C/min necessary to quench the polymer into an amorphous state. The effect of small variations in the melt crystallization temperature on the morphology and the melting behavior is discussed. DSC, hot stage polarized optical microscopy and WAXD experiments are utilized to interpret the melting behavior with respect to different causes. Some indirect evidence suggests that the two prominent melting endotherms may be due to different crystal unit cell structures. For crystallization temperatures higher than 350°C, an isothermal lamellar thickening phenomenon occurs with significant increases in the peak melting point (10–14°C) observed for longer crystallization times.

The influence of blend composition on volume relaxation behavior was determined for miscible blends of poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN). The volume relaxation rates displayed an approximately linear dependence on blend composition for all of the aging temperatures employed which were 15, 30, and 45°C below Tg. No unique behavior was observed for the blends compared to the pure polymers in terms of glass transition fragility observed by differential scanning calorimetry or the variation of density with composition. The dynamic mechanical β-relaxation process for PMMA was observed in the PMMA/SAN blends, and the intensity of the relaxation diminished with increasing SAN content. These results were contrasted with previous findings by the present authors on blends of atactic polystyrene (a-PS) with poly(2,6-dimethyl phenylene oxide) (PPO). Fragility, density, and secondary relaxation features of the PMMA/SAN and a-PS/PPO blends were influenced by the respective nature of interactions in these mixtures, and the volume relaxation rates were consistent with these characteristics. An apparent failure of time–aging time superposition was noted for PMMA due to overlapping α- and β-relaxations.