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An investigation into the irradiation of physically aged glassy polymers has lead to further refinements of a previous study. Polymers used in this investigation were: polycarbonate, polystyrene, and poly(ethylene terephthalate). In this work we have followed up an earlier study in which it was observed that the characteristic DSC enthalpy relaxation peak associated with physical aging was reduced when the sample was irradiated with an electron beam accelerator below T g . This reduction was proportional to the dose the sample received. In this work we have investigated the volumetric changes that occur in these samples as well as further enthalpic relaxation studies. It was found through the use of the classical Charlesby-Pinner analysis that there exists a strong correlation between the scission G value, G (s), and little if any for the cross-linking G value, G (x) with the enthalpic relaxation behavior. This leads us to modify our earlier hypothesis and conclude that the phenomenon is primarily caused by internal energy changes manifested in endgroup creation through main chain scission during irradiation and not accompanied by the typical density changes associated with physical aging.

The diffusion and growth of an inorganic phase, namely, silica (obtained by reacting tetraethyl orthosilicate) in poly(methyl methacrylate) (PMMA), has been studied using small-angle X-ray scattering as well as electron microscopy. Previous workers have documented some of the structural features as well as the mechanical properties of such a composite system. In this work an emphasis has been placed on the fractal characteristics of the microscopic particles observed utilizing small-angle X-ray scattering. Fractal characteristics of the silica particles have been studied while varying the tetraethyl orthosilicate content with respect to PMMA. The growth of these particles in PMMA was also studied as a function of the reaction media. Typically, the silica forms mass fractals when reacted in a solvent media of tetrahydrofuran. When a small amount of dimethylformamide is added to the reaction, the fractal dimension varies from surface to mass fractal depending upon metal alkoxide content.

A new method for the production of foamed thermoplastic polymers from blends of a poly(aryl ether ketone) (PAEK) and polyetherimide (PEI) is presented. The blowing agent for the foaming process is water which is produced at elevated temperatures in an extruder, via an in situ reaction between an amine end group on the PEI, and a ketone functionality on the backbone of the PAEK chain. The effect of composition, mixing, time, and temperature are investigated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1543–1550, 1997

Lamellar thickness and its distribution in high-density polyethylene (HDPE) films having a well-defined stacked lamellar morphology were investigated by using differential scanning calorimetry (d.s.c.), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). It was found that the most probable lamellar thicknesses from SAXS and TEM agrees very well; however, they do not agree with those values obtained from d.s.c. and AFM. It is pointed out that the use of d.s.c. as a tool to determine lamellar thickness and its distribution is so sensitive to the rate of heating in the d.s.c. experiments and the parameters in the Gibbs-Thomson equation that it is not believed to be suitable for routine quantitative analysis.

Fiber spinning and extrusion, which result in preferred molecular orientation for polyethylene, have been investigated for many years [1,2]. Particular effort has been undertaken to study the mechanism of molecular orientation on the structure and properties of polyethylene extruded blown films [3-5]. In 1994, Simpson and Harrison investigated the effect of processing parameters on the crystalline and amorphous morphologies in high density polyethylene (HDPE) blown films [3]. In their study, the crystalline structure in the polyethylene blown films was suggested to be a row nucleated structure. The development of the chain folded lamellae, which grow radially from the extended chain row nuclei, were found to be strongly dependent on the processing variables: take-up ratio, blow-up ratio and frostline height. Later, Fruitwala et al. examined the crystalline orientation and morphology for both HDPE and linear low density polyethylene (LLDPE) blown films [5]. The c-axis orientation in which the c-axis of the PE crystal unit cell mainly lies in the machine direction, was observed in the blown film HDPE systems. On the other hand, the LLDPE blown films were observed to possess preferential a-axis orientation with the a-axis of the PE crystal unit cell oriented toward the machine direction.

Porous silica gels with high surface area were prepared by calcination of silica/poly(tetramethylene oxide) (PTMO) hybrid network materials. The variation of the surface area of these silica gels with PTMO/silica composition and molecular weight of PTMO was investigated. Surface area analysis showed that for all oligomeric molecular weights of PTMO, high values in the range 700−1000 m2 g-1 could be obtained. The optimum PTMO/TEOS weight ratio was 30−50. Pore size analysis indicated that samples with high surface areas were mesoporous, while samples with low or medium surface areas were microporous. This unusual result was obtained as a consequence of the particle size of the materials, small for the high surface area materials and large for the low surface area materials. The hysteresis in the adsorption−desorption isotherms indicated that the pores were cylindrical in shape.

In this study the microphase separation and structural organization of the hard segment domains were studied as a function of diethanolamine (DEOA) content for two series of model foams based on toluene diisocyanate (TDI) and glycerol initiated ethylene-oxide-capped propylene-oxide or glycerol initiated propylene-oxide. It was found that as the DEOA content was increased, the more disordered the hard segment domains became. Extractions in dimethyl formamide (DMF) showed that increasing the DEOA content increased the gel fraction, confirming that DEOA further crosslinked the system. More importantly, it was also found that the hard segment domains were also influenced by the DEOA content where the foams lacking DEOA had a much higher level of short range ordering. This was first confirmed by wide-angle x-ray scattering (WAXS) patterns where the amorphous character was much more pronounced as the DEOA content was increased. In addition, Fourier transform infrared (FTIR) data from the carbonyl region showed that the level of bidentate urea or strong hydrogen bonding also decreased as the DEOA content was increased, confirming that the short range ordering does decrease with increased DEOA content. This observation is believed to help explain the greater ease of “plasticization” by temperature and moisture observed of foams that included DEOA in their formulation. This was exemplified by comparing the load relaxation behavior at a low temperature (35°C) and a high temperature (100°C) between two foams varying in DEOA content. At ambient conditions (40°C, 35%RH), the foam with DEOA exhibited slightly higher loads at any given loading time, while at elevated conditions (100°C, 98%RH), there was very little difference between the two foams. Although the observed load relaxation behavior was mostly a result of the increased crosslinking, the increased closed cell content induced by the greater crosslinking also contributed to the load values. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:525–537, 1997

Spherulitic growth rate and morphological studies carried out on a novel poly(ether ether sulfide) yielded dual spherulitic morphologies at all crystallization temperatures. Distinct populations of two kinds of spherulites were formed, with a population of coarse-textured spherulites exhibiting higher growth rate (Type II) than a population of fine-textured spherulites (Type I), at all temperatures studied. The growth rate dependence on temperature for the Type I spherulites was consistent with the theoretically predicted “bell-shaped” curve, indicating nucleation-controlled growth at temperatures close to the melting temperature and diffusion-controlled growth at temperatures closer to the glass transition temperature. The growth rate of the Type II spherulites, however, surprisingly did not exhibit any diffusion-controlled regime, with the growth rate increasing with decreasing temperature across the whole range of temperatures studied here. The above described phenomenon was found to be indepe...

The solid-state ordered structures formed by low M a ionic diblock copolymers of less than 10,000 g/mol, made by group-transfer polymerization of methacrylates, were studied. The unquaternized diblocks exhibit no structure via small-angle x-ray scattering (SAXS) and are apparently below their critical value of XN in a disordered melt state at room temperature. However, the amine salt ionomers exhibit morphologies ranging from dispersed spheres to lamellae which were investigated by SAXS and transmission electron microscopy (TEM). The morphology depends strongly on the size and proportion of the blocks, the extent of quaternization, and the concentration of the blocks in the casting solution.

In this study the viscoelastic and compression set properties were studied as a function of temperature and humidity for a series of moulded foams based on toluene diisocyanate (TDI) and glycerol initiated ethylene-oxide-capped propylene-oxide. The results were compared to those obtained on conventional slabstock foams based on TDI and glycerol initiated propylene-oxide. These comparisons were made to delineate and clarify distinct differences between these two different but very important systems. It was found that high temperatures and humidities ‘plasticized’ the moulded foams to a greater extent than the slabstock foams. Moulded foams displayed a higher compression set value and higher load decay value in the viscoelastic measurements than slabstock foams. In an attempt to understand these dramatic differences, the two types of ‘cross-links’ (covalent cross-links and urea-based phase separated hard segment domains) were more directly compared. It was found that the hard segment domains in the slabstock foam had a much higher level of short range ordering and cohesiveness. This was first confirmed by comparing the wide-angle X-ray scattering (WAXS) patterns where the amorphous character was much more pronounced in the moulded systems of equal water/TDI content. The WAXS behaviour of the slabstock system distinctly displayed short range ordering of the TDI based units. Second, Fourier transform infrared (FTi.r.) data from the carbonyl region showed that the slabstock foam had a much higher level of bidentate urea (strong hydrogen bonding) within the hard segments. Conversely, the moulded foam displayed no bidentate urea but only monodentate urea or weaker hydrogen bonding within the hard segments. This is not to imply that microphase separation did not occur since small angle X-ray scattering (SAXS) clearly showed evidence of a phase separated morphology for both types of foam systems. It is thus concluded that the dramatic differences between the mechanical properties of moulded and slabstock foams are due in part to differences in the covalent network but mostly due to the lower and weaker ordering of the hard segments in moulded systems making these physical cross-links more labile at higher temperatures and humidities. These morphological differences are believed to be due primarily to two differences in the formulation components and processing between the two studied systems. First, the ethylene-oxide capping used in the polyol of moulded foams to increase the reactivity is known to also increase the compatibility between the hard and soft segments. Second, the addition of diethanolamine (DEOA) added in the moulded foam formulation to decrease demould times by enhancing more rapid cross-linking has been shown to prevent the full local packing development of the hard-segment domains (physical cross-links).

Dynamic mechanical experiments were conducted on melt-extruded uniaxially oriented high- density polyethylene films having a well-defined stacked lamellar morphology. Samples were cut at different angles with respect to the original machine direction (MD) and tested by increasing the temperature from 20 to 130 °C at a heating rate of 0.5 °C/min in the frequency range from 0.01 to 10 Hz. Samples before and after the dynamic mechanical tests were also investigated by using WAXS, SAXS, and DSC. Oscillating parallel (0°) and perpendicular (90°) to the MD gave rise to a single tan δ dispersion peak, while oscillating at angles between the above two extremes generated a secondary dispersion peak at lower temperatures, with a maximum relaxation strength occurring at 45° orientation. It was concluded that, for the 0 and 90° orientations, the mechanical dispersion arises essentially from the crystalline phase, and it contains the contributions of earlier recognized intralamellar (αI) and intracrystalline (αII) rel...

The synthesis of controlled molecular weight semicrystalline polyimides based on 1,3-bis(4-aminophenoxy)benzene (TPER diamine) and 3,3‘,4,4‘-biphenyltetracarboxylic dianhydride (BPDA), end capped w...

Sulfonated polyisobutylene (PIB) telechelic ionomers with narrow molecular weight distribution (MWD) have been recently developed, providing additional control over the structure and properties of these novel polymers. A small angle X-ray scattering (SAXS) peak often associated with the aggregation of the ionic species in the bulk, and a secondary peak, were recently observed in the narrow MWD sulfonated PIB telechelics for the first time. SAXS evidence, given earlier as part I of this two-part series, suggests that compression-molded sulfonated PIB telechelic ionomers with a narrow MWD (M¯w/M¯n ≈ 1.15) may have a local secondary structure of ionic lamellae or cylinders, and no such structure is found in similar broad MWD (M¯w/M¯n ≈ 1.8) telechelics. It is shown that narrowing the MWD, which acts to promote locally continuous structure in the tri-arms, alters the character of the network, in that the modulus of the tri-arm telechelic systems increases and the elongation at break is lowered by narrowing the MWD or decreasing the M¯n. The tri-arms of the highest M¯n (49.5 kg/mol) exhibit strain hardening and the lowest modulus, highest-breaking stress, and highest elongation at break in the ionomers studied. The presence of local ionic structure is also indicated by stress relaxation experiments in which the long-term or near-equilibrium stress is seen to decrease when the MWD is broadened or M¯n increases. It is believed that the difunctional materials do not form extensive ionic networks at all, but principally chain-extend, as has also been found before. It is observed that the properties of a solution “blend” of narrow MWD ionomers that has the same counterion, M¯n, and polydispersity as a broad MWD system exhibits lower elongation to break, lower breaking stress, and modulus of narrow MWD systems relative to the broader MWD material. Dynamic mechanical data indicate that narrowing the MWD or decreasing M¯n increases the flow transition temperature and rubbery plateau modulus. The “blend” exhibits dynamic mechanical properties between the narrow and broad, having a higher flow transition temperature than the broad MWD, but lower than the narrow MWD, and a rubbery plateau modulus between the other two. © 1997 John Wiley & Sons, Inc.

An aminolysis mechanism is proposed to explain the enhanced adhesion between the interface of a bisphenol-A polycarbonate substrate with an alkoxysilane containing sol-gel coating when 3-aminopropyltriethoxysilane (3-APS) is used as a primer. Both a model solution study and surface analyses of polycarbonate substrates exposed to 3-APS indicate that the latter reacts with the carbonate groups in the polycarbonate chain by forming urethane linkages. With 3-APS bonded to the substrate, a sol-gel coating can be chemically bonded to the substrate through hydrolysis of alkoxysilane groups and subsequent silanol condensation. Consequently, enhanced adhesion between the sol-gel coating and the substrate is achieved.

Two-dimensional angular correlation of annihilation radiation (2D-ACAR) experiments have been performed on a uniaxially oriented polymer, bisphenol-A polycarbonate. The two-dimensional hole structures of unoriented and oriented polymers, determined from the momentum distributions, are found to be spherical and ellipsoidal, respectively. The average hole radii are determined to be 2.9 A in the unoriented sample and between 2.3 and 3.8 A in the oriented sample. Applications of the 2D-ACAR method to image the three-dimensional hole structures of polymeric materials are discussed.

Cellular materials were generated from radiation curable compositions of acrylated monomers and oligomers utilizing electron beam irradiation techniques. The relationships between the processing variables, the chemical compositions, and the final properties of these materials were examined. Two methods of producing these materials were compared. One process consists of frothing the radiation curable mixture before irradiation by a mixing technique and then casting the unpolymerized froth onto a substrate where it can be subsequently cured using electron beam radiation. Another process relies on a surfactant to stabilize the cellular structure before irradiation. It was found that the quality of the cellular structures produced by these techniques is highly dependent on the viscosity of the radiation curable mixture. A detailed outline of these processes with the resultant structures and properties of these cellular materials is presented along with comparison with other cellular material generation processes. © 1996 John Wiley & Sons, Inc.

The structure—property behaviour of high density polyethylene (HDPE) extruded tubular films having a blow up ratio of unity was investigated. Two different HDPE resins with identical M n (14 600 g/mol) values but different distributions ( M w M n = 10.3, 15.1 ) were utilized in this extrusion process. Systematic changes were also made in the process variables—these being the melt temperature at the die exit, the quench height, which is the distance from the exit of the die to the cooling ring, the flow rate of the air through the cooling ring, and the film line speed. The morphological features and state of orientation of the extruded tubular films were examined by transmission electron microscopy (TEM), high resolution scanning electron microscopy (HSEM), birefringence, wide and small angle X-ray scattering studies (WAXS, SAXS), and linear infra-red (i.r.) dichroism. A stacked lamellar or, in some cases, a fibril nucleated morphology was observed in the melt-extruded films by TEM. This technique clearly showed that the broader molecular weight samples possessed fibril nuclei that were not evident in the narrower molecular weight distribution films. The existence of the fibril nuclei was further confirmed from WAXS by the intense sharp spots superimposed on the equatorial (110), (200), and (020) reflections. The origin of this pronounced fibril nucleation was clearly believed to be due to the longer relaxation time behaviour of the broader distribution resin. The amorphous phase orientation and form birefringence for all films were found to be very small, and the observed birefringence arose almost exclusively from the crystalline phase. It was also found that the morphology and the orientation of the chain axis in the crystalline phase were particularly sensitive to the quench height and melt temperature for the narrower distribution HDPE films, but much less so for the broader distribution HDPE samples. Little dependence of structure/orientation was noted for either resin for the variables of the flow rate of the air through the cooling ring and the film line speed. These findings show the sensitivity of the molecular weight distribution to be a very important parameter, as are the specific processing variables of quench height and melt temperature, in determining the final solid state structure of the HDPE extruded tubular films.

The crystallization behaviour of poly(p-phenylene sulfide) (PPS) has been studied. Two PPS samples with 〈MW〉 = 44 K and 〈MW〉 = 64 K were fractionated by a process which selectively removes a portion of the low molecular weight species yielding fractionated PPS samples with 〈MW〉 = 56 K and 〈MW〉 = 104 K respectively. The fractionated samples were then treated with an ion exchange process to allow control over the nature of endgroup counter-ion, i.e. to introduce Na+ and Zn2+ ions. Using a Hoffman-Weeks analysis, the equilibrium melting temperature of these polymers was estimated to be 320°C irrespective of endgroup counter-ion or polymer molecular weight. The nucleation density was observed to increase as a function of molecular weight by small-angle light scattering (SALS). The spherulitic growth rates and nucleation densities were studied as a function of the chemical nature of endgroup counter-ion for PPS with 〈MW〉 = 56 K that had been fractionated to remove low molecular weight species. Additionally, isothermal rates of bulk crystallization were analysed as a function of molecular weight of PPS and chemical nature of the endgroup counter-ion. It was found that as a function of endgroup counter-ion, crystal growth rates and overall crystallization rates decreased in the following order: H+ > Zn2+ > Na+. The order of decreasing crystal growth rates corresponded to a similar increase in melt viscosity as a function of endgroup counter-ion, suggesting that the reason for decreasing growth rates could originate from increasing secondary interchain interactions. Optical microscopy studies showed the nucleation density decreased in the order H+ > Na+. The ion-exchange reactions were shown to be reversible by differential scanning calorimetry (d.s.c.) and optical microscopy studies. Crystallinity determinations by wide angle X-ray diffraction (WAXD) and measurements of the heats of melting illustrated that higher molecular weight PPS attained lower levels of crystallinity than PPS of lower molecular weight when crystallized under identical conditions.

Styrene-butadiene multiblock copolymers were examined with both newly introduced and established rheological techniques and by transmission electron microscopy (TEM) to evaluate shear-induced structural changes in these polymers. Transient rheological tests (based on superposed flow principles) were developed which probed structural changes that occur in the copolymers during and at the cessation of steady shear. Data from these tests indicated that for the cylindrical morphology copolymer (SB1) there were structural changes occurring during steady shear that were recovered upon cessation of shear. The recovery process took place on time scales that could be significant in processing. The lamellar morphology material (SB2) did not exhibit this recovery behavior. Longer-term structure changes were investigated using established techniques and showed differences between the cylindrical and lamellar copolymers. When tested at 210°C, peaks in tan δ occurred at 30 rad/s for SB1 and at 0.5 rad/s for SB2 with saturation strain levels of 150 strain units (SU) for SB1 and 80 SU for SB2. TEM analysis of SB2 indicated that, although rheological changes are significant up to 80 SU, better alignment of the domain morphology can be achieved at moderately low strains of 7 SU. This indicates that the copolymers' rheological changes, which occur as a result of steady shearing, may not be due entirely to domain alignment, but may also be due to more local molecular rearrangements (e.g., chain disentanglement). © 1996 John Wiley & Sons, Inc.

Triethoxysilane groups were covalently attached onto the surface of ethylene-vinyl alcohol (EVOH) copolymer film via a urethane linkage through reaction between the hydroxyl groups in EVOH and 3-isocyanatopropyltriethoxysilane in the presence of dibutyltin dilaurate as catalyst. This reaction was confirmed by ATR-IR and XPS analysis. XPS results also indicated that this reaction was not surface sensitive and the modified layer was at least 40 A in depth. The modified film samples were further reacted with tetramethoxysilane (TMOS) for partial hydrolysis and condensation and XPS results showed a significant increase in the contents of oxygen and silicone on the surface which confirmed the above reaction.

Novel high performance semicrystalline polyimides, based on controlled molecular weight phthalic anhydride (PA) endcapped 1,4-bis(4-aminophenoxy)benzene (TPEQ diamine) and oxydiphthalic dianhydride (ODPA), were synthesized. They exhibited excellent thermal stability in nitrogen and air atmospheres as determined by thermogravimetric analysis (TGA). The glass transition temperatures (T g ) for these polymers ranged from 225°C for the 10,000 M n (10K) polymer, to 238°C for the 30,000 (30K) M n material. The observed melting temperatures for all the polymers were ∼420°C. The crystallization behavior of these polymers showed a strong molecular weight dependence, as illustrated by the observation that the 10K and 12.5K polymers crystallized with relative ease, whereas the 15K, 20K, and 30K polymers showed little or no ability to undergo thermal recrystallization. The thermal stability of these polymers above T m was investigated by studying the effect of time and temperature in the melt on the cold crystallization and melting of these polymers. Increased time and temperature in the melt resulted in lower crystallinity because of melt state degradation, such as crosslinking and branching, as evidenced by an increase in melt viscosity, which was more prominent for the higher molecular weight polymers.

The influence of changing the block length of the polydimethylsiloxane block on the structure/property behaviour of two poly(ether ether ketone)-polydimethylsiloxane (PEEK-PSX) multiblock copolymers and their amorphous (non-crystallizable) ketamine precursors (PEEKt-PSX) was investigated. In the precursor block copolymer form, as well as the reduced amorphous and its corresponding semicrystalline form, a microphase morphology was noted from transmission electron microscopy (TEM) studies. For the solution cast precursor or the compression moulded reduced amorphous systems, the materials displayed two Tgs at ca. −130 and +145°C, indicating strong phase separation. It was found that the room temperature tensile modulus of the PEEK-PSX multiblock copolymers with amorphous PEEK blocks of M n = 4000 increased by 800% as the PSX block length was decreased from M n = 5000 to M n = 3000 , i.e. the PSX mass fraction was decreased from 56 to 45%. This increase in stiffness resulted from developing a more continuous phase of the PEEK block component. After crystallization of the PEEK blocks, the room temperature modulus of both of the PEEK-PSX copolymers increased by 200–500% in contrast to their amorphous forms. Relative to the PEEK homopolymer of approximately the same molecular weight, the melt crystallization half-times for the multiblock copolymers were increased by a factor of 500 for the PEEK(4K)PSX(3K) system and by a factor of 1000 for the PEEK(4K)PSX(5K) system. A dramatic dependence of crystallization behaviour on thermal history prior to crystallization was observed in both microphase-separated block copolymer systems. Block copolymers thermally crystallized from the glassy state obtained a distinctly higher degree of crystallinity at a much faster rate of crystallization than the same copolymers crystallized from the melt at identical crystallization temperatures. Copolymers crystallized from the glass attained maximum levels of PEEK crystallinity of ~ 40%, while those crystallized from the melt attained a maximum level of crystallinity of only 5–20%. The rate of crystallization for samples crystallized from the glass was ~ 30 times greater than that for samples crystallized from the melt at identical crystallization temperatures. Possible explanations for these observations are presented.

Organic/inorganic hybrid materials prepared by the sol−gel approach have rapidly become a fascinating new field of research in materials science. The explosion of activity in this area in the past decade has made tremendous progress in both the fundamental understanding of the sol−gel process and the development and applications of new organic/inorganic hybrid materials. In this review, a brief summary of the research activities in the field of organic/inorganic nanocomposite materials and a general background of the sol−gel chemistry are first given. The emphasis of this report, however, is placed on the synthesis, structure−property response, and potential applications of the organic/inorganic hybrid networks that possess chemical bonding between the organic and inorganic phases, particularly those systems that were developed in our laboratory since 1985.

The synthesis of inorganic organic hybrid materials has been undertaken and used as abrasion resistant coatings for polymeric substrates by the sol-gel method. The organic components are diethylenetriamine (DETA), glycerol, and a series of aliphatic diols which are functionalized by 3-isocyanatopropyltriethoxysilane. The inorganic components are tetramethoxysilane (TMOS), aluminum tri-see-butoxide, titaniumsec-butoxide and zirconiumn-propoxide. Solutions of these materials are spin coated onto bisphenol-A polycarbonate sheet and thermally cured to obtain a transparent coating of a few microns in thickness. Following the curing, the abrasion resistance is measured and compared with a control having no coating. It was found that the abrasion resistance of inorganic organic hybrid coatings in the neat form or containing additional silicon, titanium, zirconium, and aluminum alkoxides can be very effective to improve abrasion resistance. The adhesion tests show that the adhesion between coating and substrate can be greatly improved by treating the polymeric substrate surface with an oxygen plasma or a primer solution of isopropanol containing 3-aminopropyltriethoxysilane. Other experiments, such as the abrasion resistance tests following conditioning in a “hot-wet” condition (boiling water treatment), microhardness tests. UV absorption behavior, and the observation of abraded surfaces, were also undertaken in order to evaluate these coating materials.

The structure-property behavior of two series of new ionomers derived from well-defined block copolymers was investigated. The two types of triblock systems were either poly(tBMA-b-BD-b-tBMA) or poly(tBMA-b-S-t-BD-t-S-b-tBMA) (tBMA = tert-butyl methacrylate ; BD butadiene ; S = styrene ; t = taper). The materials have been examined in the tert-butyl ester forms and also hydrolyzed (carboxylic acid) and neutralized to the cesium carboxylate salt. The ester precursor exhibits a morphological transformation upon neutralization in the case of a 9 mol % tBMA-BD triblock, from unoriented rodlike domains in the ester precursor to ion-containing spheroids in the ionomer. This transformation was observed by transmission electron microscopy (TEM) and also supported by the dynamic mechanical behavior of the respective systems. The introduction of styrene into the butadiene center block results in an increase in the glass transition temperature, as anticipated. However, the tapered nature of the center block in the styrenic materials promotes greater phase mixing, as supporting TEM and dynamic mechanical analysis (DMA) indicate. The composition of the center block in these tapered materials also alters the glass transition, as shown by DMA. In the tapered SBS cesium ionomers, the temperature of the transition to flow occurs at higher temperatures as the length of the ionic end block increases.

Thermal and mechanical behavior of bisphenol-A polycarbonate was studied as a function of thermal history and absorbed mass fraction of CO2. Physical aging at 120°C for one week produced dramatic changes in both the thermal and mechanical behavior. Gas absorption studies indicated that although initial diffusion was somewhat retarded in the aged samples, both aged and unaged polycarbonate samples showed identical equilibrium absorbed gas values at 6500 K Pa and identical gas desorption behavior. Absorbed CO2 was shown to dramatically reduce the glass transition of polycarbonate indicating that CO2 plasticizes polycarbonate. Additionally, samples which had been aged and absorbed a mass fraction of 0.07–0.10 of CO2 showed thermal and mechanical behavior identical to that of a glass quenched from above Tg with identical absorbed mass fraction. Once the absorbed gas was desorbed, the thermal and mechanical properties were similar to those of a glass freshly quenched from above Tg. This study demonstrates that sufficient CO2 gas absorption followed by desorption reverses physical aging in polycarbonate. © 1995 John Wiley & Sons, Inc.

Hybrid networks of functional poly(tetramethylene oxide) (PTMO) and tetraethyl orthosilicate or titanium isopropoxide were prepared through the sol gel route. The films formed by this approach were then immersed in solutions of varying alkalinity for a period of time, removed and dried. This treatment resulted in a better defined two phase microstructure in the PTMO/TEOS hybrids because of the solubility of silicon oxide in the highly basic medium. The treated hybrids exhibited higher PTMO chain mobility to the extent that the oligomeric chains could now undergo crystallization at low temperatures. The loss of silicon oxide and hydrolysis of the alkali-treated network resulted in a lower modilus than the untreated hybrid. In the PTMO/TiOPR hybrid, due to the lower solubility of titanium oxide, the base treatment resulted in little changemodulus

Nanocomposites were produced via sol–gel reactions for tetraethylorthosilicate within the cluster morphology of perfluorosulfonic acid films. Small-angle x-ray scattering revealed that the polar/nonpolar nanophase-separated morphological template persists despite invasion by the silicon oxide phase. Scanning electron microscopy (ESEM–EDAX) studies have indicated that the greatest silicon oxide concentration occurs near the surface and decreases to a minimum in the middle. Optical and ESEM micrographs revealed a brittle, surface-attached silica layer at high silicon oxide contents. © 1995 John Wiley & Sons, Inc.

The first structure-property relationships are reported for segmented polyrotaxane ionenes which possess the rotaxane moiety at the hard segment. These ionenes are based on PTMO/MDI (PTMO M n of 650, 1000, or 2000 daltons) as the elastomeric segment and paraquat hard segments with either PF6 − or Br− as the counterion. GPC indicates that these ionenes have a highly variable architecture with respect to the placement of the ionene hard segment. SAXS also supports the notion of a randomly placed hard segment because the interionic domain d spacings are not predictable or consistent. SAXS also shows there are few “lone multiplets” in the PF6 − derivative whereas there are considerable numbers of isolated ion pairs in the Br− ion-exchanged ionenes. Tensile testing shows that the PTMO-1000 and PTMO-2000 materials are elastomeric with good properties, but the PTMO-650 ionene is not elastomeric with the ionic hard segment as a continuous phase. Dynamic mechanical tests also indicate that these segmented...

The development of crystallinity during the thermal imidization of a rigid aromatic polyimide synthesized from 1,4-bis(4-aminophenoxy-4′-benzoyl)benzene (1,4-BABB) and oxydiphthalic dianhydride (ODPA) was investigated. Film samples were imidized through a stepwise procedure involving isothermal staging for 1 h each at 100, 200 and 300°C. Differential scanning calorimetry (d.s.c.), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and thermogravimetric analysis (t.g.a.) were employed to monitor changes in the crystalline state of the films during imidization. The development of crystallinity during thermal imidization was shown to progress through stages that depended upon the time and temperature of the process, wherein the final crystalline index was approximately 46%. This relationship was explained in terms of chain mobility. SAXS analysis suggests that a two-stage, lamellar in-filling process exists for the development of the final crystalline superstructure where the final long spacing is approximately 130A. Fourier transform infra-red spectroscopy ( FT i.r.) analysis does not reveal the presence of anhydride groups at any stage of the imidization process, indicating that significant chain scission did not occur during processing. Transmission electron microscopy (TEM) analysis of the stepwise imidized films reveals that crystalline growth begins at the glass surface of the film and progresses toward the air surface with increasing thermal staging. TEM analysis of a series of fully imidized films reveals that an amorphous layer remains at the air surface of the films, the thickness of which is dependent upon molecular weight.

Thermal characterization has been carried out on a series of biphenol- and hydroquinone-based novel poly(acrylene ether ether sulfide) polymers. Thermogravimetric analyses of the sulfide systems indicate high thermal stability in air as well as in nitrogen. X-ray studies showed the poly(ether ether sulfoxide) precursor materials to be amorphous and the poly(ether ether sulfide) materials to be semicrystalline. Based on the number-average molecular weight of the poly(ether ether sulfoxide) materials, and the glass transition temperatures determined by differential scanning calorimetry (d.s.c.), the limiting T g∞ has been determined for both amorphous precursors. The biphenol-based precursors sulfoxide had a T g∞ of 214°C and the hydroquinone-based precursor had a T g∞ of 179°C. D.s.c. studies showed the biphenol-based poly(ether ether sulfide) to have a T g of 142°C and T m of 347°C, and the hydroquinone-based poly(ether ether sulfide) to have a T g of 100°C and a T m of 243°C. The equilibrium melting temperature T ° m has been determined for both sulfide polymers using the Hoffman-Weeks method. The hydroquinone-based poly(ether ether sulfide) exhibited a T ° m of 278°C, and the biphenol-based poly(ether ether sulfide) showed a T ° m of 371°C. The effect of time and temperature in the melt on the subsequent crystallization behaviour of the two sulfide materials has also been investigated as a function of molecular weight.

Diethylenetriamine, melamine, and low molecular weight branched polyethylenimine were functionalized separately with 3-isocyanatopropyltriethoxysilane. Coatings on polycarbonate were prepared from these compounds through the sol-gel process. The extent of reaction and the relative species concentration of the trifunctional silicon atom were obtained from29Si CP-MAS NMR measurements. The sol-gel reaction was found to be limited by vitrification. A variety of silicon species was present in the vitrified coating. The extent of reaction could be increased by increasing the curing temperature, curing for longer times, and increasing the acid concentration. The extent of reaction was also found to be related to the basicity of the functionalized organic backbone.

New strategies for the synthesis of perfectly alternating segmented polyimide-polydimethyl siloxane copolymers were developed by utilizing a transimidization method. Imide oligomers endcapped with 2-aminopyrimidine were reacted with aminopropyl terminated (dimethyl siloxane) oligomers to afford perfectly alternating segmented imide siloxane copolymers. The polymerization was conducted in solvents such as chlorobenzene and chloroform. High molecular weight, fully imidized perfectly alternating segmented imide siloxane copolymers were obtained within 2 h at temperatures of 60-110°C. The mechanism of the reaction was further elucidated via model compounds and NMR characterization

A novel ‘3F’ fluorinated diamine monomer based on trifluoroacetophenone was synthesized via a straightforward, high yielding two-step procedure. Trifluoroacetophenone was reacted with 4-nitrophenyl phenyl ether to yield the 3F-dinitro compound, which was subsequently reduced to afford the fluorinated diamine, 1,1-bis[4-(4-aminophenoxy)phenyl]-1-phenyl-2,2,2-trifluoroethane (3FEDAM). New amorphous and semicrystalline polyimides based on 3FEDAM were prepared and characterized by differential scanning calorimetry, thermogravimetric analysis and wide-angle X-ray scattering (WAXS). In particular, the 3FEDAM-pyromellitic anhydride-phthalic anhydride material exhibited a glass transition temperature of 308°C and a melting temperature of 476°C, which are quite similar to the values reported for ‘6F’-based systems. The semicrystalline nature was confirmed by WAXS analysis, and is consistent with the excellent solvent resistance observed for these polyimides.

Linear and star-branched polyoxybenzoate–polyoxyphenoxybenzoate copolymers (POB-co-POPB) at a 65/35 molar ratio were synthesized via melt acidolysis using AB-type monomers and branching agents. By controlling the molecular weight and topology of these polymers, both melt processability and solid-state CO2 gas absorption behavior were enhanced. POB–POPB copolymers with a molar ratio 65/35 showed a glass transition of 143°C and completion of melting at ca. 300°C. POB–POBP copolymers with a systematically increasing branching agent content showed a systematically decreasing peak intensity in wide-angle X-ray diffraction, indicating that increasing branch-point concentration leads to a decrease in liquid-crystal ordering. Star-branched POB–POPB copolymers showed greatly enhanced carbon dioxide gas absorption behavior relative to their linear counterparts. Whereas CO2 blown foams of linear POB-co-POPB produced by the gas supersaturation technique had a relatively high density and showed highly anisotropic bubble growth, well-defined, nearly isotropic foams of star-branched POB-co-POPB with a mean cell size from 200 to 400 μ were made using the gas supersaturation technique. Structural features were characterized via scanning electron microscopy, and mechanical properties were determined by indentation testing with a 0.25 in. ball indenter. These LCP foams exhibit relative mechanical properties similar to polystyrene and microcellular polycarbonate foams. A strong inverse relationship was noted between cell size and modulus for liquid crystalline foams with a cell size below 400 μm. © 1994 John Wiley & Sons, Inc.

Characterization of a series of flexible polyurethane foams that contain LiCl in their formulation is discussed. These foams were developed in order to provide an alternative method to produce foams without physical blowing agents and still attempt to maintain specific important physical properties. Three high water content foams of varying LiCl content have been characterized by utilizing several morphological techniques as well as by their viscoelastic behavior. From a morphological standpoint, it appears that by adding LiCl to the formulation, there is less formation of urea-rich aggregates that occur when LiCl is absent. Also, the hard segments are more dispersed as single units within the network. The cellular texture of the LiCl-containing foams also shows a greater amount of cellular window material than the same foam without LiCl. Both of these changes due to LiCl addition are believed to bring about a significant increase in the amount of viscoelastic decay. This decay has been observed in tensile stress relaxation, compression load relaxation, and compressive creep studies. Temperature also has a more significant effect on the compression load relaxation behavior of foams with LiCl in their formulation than when absent. These differences in viscoelastic behavior between foams with and without LiCl in their formulation are attributed to the greater mobility of the hard segments in the presence of the LiCl additive serving as a localized “hard segment” plasticizer that also promotes more phase mixing in the foams. © 1994 John Wiley & Sons, Inc.

High-resolution solid-state 13C-NMR has been used to study the phase separation and molecular motion in two series of polyurethane foams. These two series differ by one possessing the additive of lithium chloride, LiCl. NMR relaxation times can map the motion throughout the polymer molecule and detect changes in that motion arising from either microseparation or phase mixing between the different segments. There are only slight changes in the soft segment T1p(13C) values as well as an increase in the hard segment T1p(1H) values with increase in the hard segment content for the foams studied. The T1p(1H) and T1p(13C) values do indicate that the phase separation of the hard and soft segments is similar for all foams. A decrease in the T1p(1H) and T1p(13C) values with increasing LiCl content indicates that the motion of the soft segments is restricted more by the hard segments. This is explained by more phase mixing in the foams containing the LiCl additive. © 1994 John Wiley & Sons, Inc.

The compression creep behavior was monitored at constant temperature and/or relative humidity for two slabstock foams with different hard-segment content. The tests were performed by applying a constant load (free falling weight) and then monitoring the strain as a function of time over a 3-h time period. A near linear relationship is obtained for linear strain versus log time after a short induction period for both foams and at most conditions studied (except at temperatures near and above 125°C). The slope of this relationship or the initial creep rate is dependent on the initial strain level, espcially in the range of 10–60% deformation. This dependence is believed to be related to the cellular structs buckling within this range of strain. At deformations greater than 60% and less than 10%, the solid portion of the foam is thought to control the compressive creep behavior in contrast to the cellular texture. Increasing relative humidity does cause a greater amount of creep to occur and is believed to be a result of water acting as a plasticizer. For low humidities increasing the temperature from 30 to 85°C, a decrease in the rate of creep is observed at a 65% initial deformation. At 125°C, an increase in the creep rate is seen and is believed to be related to chemical as well as additional structural changes taking place in the solid portion of the foams. The creep rate is higher for the higher hard-segment foam (34 wt %) than that of the lower (21 wt %) at all of the conditions studied and for the same initial deformation level. This difference is principally attributed to the greater amount of hydrogen bonds available for disruption in the higher hard-segment foam. © 1994 John Wiley & Sons, Inc.

The relaxation behavior of the load in compression and the stress in tension was monitored at constant temperature and/or relatively humidity for a set of four slabstock foams with varying hard-segment content as well as two of the compression molded plaques of these foams. The majority of the compression relaxation tests were done at a 65% strain level in order to be consistent with the common ILD test. The tensile stress relaxation tests were performed at a 25% strain level. Over the 3-h testing period, a linear relationship between the log of compressive load or the log of tensile stress versus log time is observed for most testing conditions. For linear behavior, the values of the slope or the load/stress decay rate are comparable in both the tension and compression modes with the values being slightly higher in magnitude for the compression mode. These rates of decay are in the range of −2.2 × 10 −2 to −1.7 × 10 −2 for a 21 wt % hard-segment foam and −3.2 × 10−2 to −2.4 × 10−2 for a 34 wt % hard-segment foam. Increasing %RH at a given temperature does bring about a steady decrease in the initial load or initial stress as well as a slight increase in the rate of relaxation. The effect of temperature on the relaxation behavior is most significant at temperatures near 125°C and above. The FTIR thermal analysis of the plaques indicates that this significant increase is due to additional hydrogen bond disruption and possible chain scission taking place in the urea and urethane linkages that are principally present in the hard segment regions. The relaxation behavior in both tension and compression is believed to be mostly independent of the cellular texture of the foam at the strain levels given above. This conclusion is based on the similar relaxation behavior between the plaques and the foams. © 1994 John Wiley & Sons, Inc.

Novel abrasion-resistant coatings prepared by a sol-gel process have been developed and applied on the polymeric substrate Bisphenol A polycarbonate. In general, coatings utilize either 4,4′-diaminodiphenyl sulfone (DDS) or diethylenetriamine (DETA) that are then functionalized at their amine groups with 3-isocyanatopropyltriethoxysilane. Following functionalization, these coating materials are then spin coated onto bisphenol A polycarbonate sheet and cured. These reactants undergo a comparable sol-gel reaction similar to typical metal alkoxide chemistry, thereby producing an insoluble network material containing a good dispersion of the functionalized organic along with the hydrolyzed and condensed silicon alkoxide groups. The final coating is transparent and of a few microns in thickness. Following curing, an index of the abrasion resistance is assessed by an optical method, and the adhesion behavior of the coatings is investigated and quantified. It is demonstrated that these thin transparent ...

The dual melting behaviour of a rigid aromatic polyimide synthesized from 1,4-bis(4-aminophenoxy-4′-benzoyl)benzene and oxydiphthalic dianhydride was analysed. Film samples were synthesized through a stepwise imidization procedure wherein molecular weight control was effected through stoichiometric offset. The films display a glass transition temperature of 217°C and dual endothermic transitions at ca. 334°C and 364°C. Transmission electron microscopy, wide angle X-ray diffraction and small angle X-ray scattering (SAXS) studies, in conjunction with dynamic scanning calorimetry (d.s.c.) analysis, show that the higher melting transition results from the melting of lamellae which were melt recrystallized during heating in the d.s.c. D.s.c. heating rate studies reveal that the rate of transformation from thin to thick lamellae is dependent upon molecular weight, as expected. Synchrotron SAXS analysis confirms that the melt recrystallization process is very rapid for this high glass transition, low molecular weight polymer.

Novel fumed silica filled thermoplastic poly(dimethylsiloxane-urea) (TPSU) segmented copolymers were synthesized and characterized. TPSU copolymers were prepared from a cycloaliphatic diisocyanate, aminopropyl terminated PDMS oligomers with number average molecular weights of 3,200, 10,800 and 31,500 g/mol and 2-methyl-1,5-diaminopentane chain extender. Two different types of fumed silica HDK H2000 (hydrophobic) and HDK N20 (hydrophilic) were utilized and incorporated into silicone-urea copolymers in amounts of 1-60% by weight. Influence of the silica type (hydrophilic versus hydrophobic), amount of silica loading and the PDMS soft segment molecular weight on the morphology, tensile properties and modulus-temperature behavior of the nanocomposites were determined. Major observations of this study were: (i) under the blending conditions used, incorporation of silica does not seem to interfere significantly with the hydrogen bonding between urea groups, (ii) incorporation of silica does not affect the glass transition temperature of PDMS, (iii) incorporation of silica influences the tensile and thermomechanical properties of silicone-urea segmented copolymers significantly, (iv) average molecular weight of the PDMS soft segment in the silicone-urea copolymer plays a critical role on the improvement of the tensile properties of the fumed silica/TPSU composites. (C) 2011 Elsevier Ltd. All rights reserved.

Over the last 2 years the sol gel technique has become very popular because of its ability to yield multicomponent inorganic glasses at low temperatures. More recently techniques to incorporate functionlized organic species into a sol gel network of metal alkoxides have been developed and studied in our laboratory as well as others. Most of these studies have focussed on the structure-property behavior of these materials, with an emphasis on understanding the properties in terms of the level of microphase separation that occurs during the network buildup in these systems. While much has been gained in this respect, the desire exists to characterize better the structure of the inorganic phase in such systems, and in this respect, utilization of small-angle X-ray scattering profiles can provide information about this structure through fractal analysis. The work discussed here focuses specifically on the fractal character of specific ceramer materials produced as a result of the reaction between tetraethylorthosilicate and end-functionalized polytetramethylene oxide. It is shown that the cosolvent system utilized to compatibilize the reactants plays a very important role in development of the structure of the inorganic phase in these hybrid materials.

Fibers were spun from isotropic and anisotropic DMAc solutions of cellulose esters. Take-up speeds of the dry jet/wet spinning process varied. Water served as the coagulant. The mechanical properties of the fibers increased as spinning progressed from the isotropic to the anisotropic state of the solution. A trade-off in solubility and fiber properties was noted as the butyryl acetyl ratio decreased. Whereas high butyryl content enhances both overall solubility and the formation of liquid-crystalline solutions at lower concentration, it results in lower fiber modulus and strength

The effects of different plasticizers on the structural features of PVC were investigated. Particular emphasis was on the fine structure as denoted by small-angle X-ray scattering (SAXS). The influence of plasticizer content on the mechanical response was followed by dynamic mechanical spectroscopy. The particular plasticizers investigated principally were diethylhexyl succinate and dibutyl phthalate, although other phthalate plasticizers were investigated including dibutyl succinate and dibutyl sebacate. It was noted that structural features at the 100– to 200–a level were systematically influenced by the type and amount of plasticizer and in particular by its solubility parameter. To account for the observed behavior, a model was proposed which speculates that the absorption of plasticizer is nonuniform within the system and in particular within the local regions where crystallites exist. The level of swelling of plasticizer into the amorphous regions at some distance from the crystallites is d...

Trialkoxysilane functionalized bis and trismaleimide based systems have been synthesized and used for coating a bisphenol-A polycarbonate substrate by the sol-gel method. The abrasion resistance of the substrate is improved by the optically clear materials following thermal curing of the coating.

It has been found that electron beam irradiation of physically aged, glassy polymeric films results in an apparent reversal of physical ageing (i.e. ‘deageing’) as determined by differential scanning calorimetry and yield stress behaviour. This is the first reported observation of ‘deageing’ in glassy polymers that does not involve heating above the glass transition or an imposed deformation process. Effects of dose level and dose rate on the physically aged state of polystyrene, poly(methyl methacrylate) and polycarbonate have been determined. The specific deageing behaviour has been found to be material-dependent and the extent of deageing is proportional to the total absorbed dose. The experimental results support a proposed hypothesis that this deageing phenomenon is the result of radiation-induced internal gas evolution, which produces an increase in free volume and corresponding reversal of physical ageing.

This work describes the crystallization behaviour and morphological features of the semicrystalline polyimide known as LARC-CPI. The study considers several features affecting crystallization behaviour such as inherent viscosity, crystallization temperature, melt temperature and time in the melt. Crystallization kinetics data were analysed using an Avrami analysis in conjunction with differential scanning calorimetry. Complications encountered when evaluating the crystallization exotherm for this analysis are also discussed. Morphological features were investigated using several techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide-angle X-ray scattering (WAXS), and small-angle X-ray scattering (SAXS). A permanganic etching technique combined with SEM successfully revealed morphological detail further supported by TEM results. This technique is also used to estimate the isothermal linear crystalline growth rate, G. The SEM and TEM data lend support to the Avrami data obtained by crystallization kinetics. SAXS results reflect the influence of crystallization temperature on the long spacing. SAXS also reveals the presence of a broad second scattering peak for semicrystalline samples which appears in the same position regardless of crystallization temperature or inherent viscosity. Molecular modelling predicts a low-energy helical conformation with a near-periodic repeat distance corresponding to that of the second SAXS peak. The periodic character of this conformation is offered as a hypothesis for that peak. This work also considers the effect of potential nucleating agents on the recrystallizability of a higher inherent viscosity LARC-CPI. One of the several nucleators investigated appears effective in enhancing the bulk crystallization rate.