bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal and dilute‐solution properties of zwitterionic copolymers
Authors: Cardoso Judith , Manero Octavio
Published: April 2003

We report the synthesis, characterization, thermal and dilute‐solution properties of zwitterionic copolymers of the sulfobetaine type, where the proportion of ionic groups is varied over a wide range. Two different structures are considered: poly (2‐vinyl pyridine sulfopropyl betaine) and poly (4‐vinyl pyridine sulfopropyl betaine). Synthesis is carried out to obtain random copolymers which are further characterized and their ionic content determined. At low proportions of ionic groups, the behavior is similar to that observed in ionomers, with substantial differences between the two structures, Increased interaction among the zwitterionic groups at higher charge densities is evidenced, which leads to the formation of clusters and agglomerates. An increase in the intrinsic viscosity with salt content in aqueous solutions is also observed. This behavior is analogous to that of homopolymers with 100% ionic content, but with particular features of interest.
Influence of polydispersity and amine–epoxide ratio on molecular mobility in epoxy networks
Authors: Iannacchione G. , Von Meerwall E.
Published: April 2003

Using nuclear magnetic resonance (NMR) T2 relaxation and pulsed‐gradient spin‐echo diffusion experiments at 175.5°C, molecular motions of the sole and gel of several epoxies of the type diglycidyl ether of bisphenol‐A (DGEBA; Shell Epon 1007F and 1009F) cured with 4,4′‐diaminodiphenyl sulfone (DDS) have been studies as a function of curative content. It was found that the fraction of protons associated with the shorter T2 component cannot be identified as the gel fraction until the substantial bimodal polymer polydispersity is accounted for in the spin relaxation model. The gel fraction and both relaxation rates have maxima near curing stoichiometry, and fall off more rapidly on the curative‐poor side. The diffusion spectrum of the sol fraction was consistent with a light species (Epon 828 remnants) plus a polydisperse (M̄w/M̄n ≅2) heavier species, in agreement with resin and sol gel permeation chromatography (GPC) results. Numerical simulations also show that polymer polydispersity is likely to affect the interpretation of T2 relaxation found in the literature.
Microrheology of high‐polymer solutions
Authors: Montfort J. P. , Tonck A. , Loubet J. L. , Georges J. M.
Published: April 2003

A new surface force apparatus is used for investigating the viscoelastic properties of high‐polymer solutions or polymer melts confined between two solid surfaces. We describe the experimental setup and discuss how to obtain the rheological behavior of the liquid from the transfer function given by two capacitance displacement transducers. In particular, we point out that for a distance between the surfaces enclosing a thin film below some thousands of Angströms, the elastic deformation of the solids is no longer negligible. Experiments conducted on a semidilute solution of polybutadiene show the applicability of the device for study of the dynamic properties of thin‐film polymers.
Epitaxial growth of isotactic polypropylene on oriented polyethylene from solution
Authors: Kawaguchi Akiyoshi , Okihara Takumi , Murakami Syozo , Ohara Masayoshi , Katayama Ken‐Ichi , Petermann Jürgen
Published: April 2003

Oriented polyethylene (PE) films with surfaces bounded by the (100) plane were prepared. On the film surfaces, isotactic polypropylene (iPP) was crystallized epitaxially from solution as quadrits with their sides parallel and perpendicular to the polyethylene chain axis. In the through wide‐angle x‐ray diffraction pattern (taken with incident x‐rays normal to the polyethylene film surface), the 111 iPP reflections was observed on the meridian (Parallel to the polyethylene chain axis). In the edge patterns (taken with x‐rays incident on the edge of the polyethylene film), 040 and 060 reflections were observed on the equator. From the diffraction patterns, the following lattice coincidence was observed between polyethylene and isotactic polypropylene: (010)iPP//(100) PE, [101]iPP//[001] PE. The Small‐angle x‐ray scattering patterns showed that edge‐on isotactic polypropylene lamellae 9 nm thick were arranged with their long axes inclined at an angle of 40° from the polyethylene axis. Molecular chains were oriented within the lamellae normal to the surfaces.
Gas transport in poly [bis(trifluoroethoxy) phosphazene] above the T(1) transition
Authors: Mizoguchi Keishin , Kamiya Yoshinori , Hirose Takuji
Published: April 2003

Gas permeation measurements were performed by the time‐lag method for 13 gases in poly [bis(trifluoroethoxy) phosphazene] above the mesophase transition, T (1) transition, of the crystals. Hysteresis was found in the temperature dependence of the permeability coefficients for CO2, O2, and N2 in the transition region as observed by dilatometry and differential scanning calorimetry. Independently the solubility of CO2 was determined gravimetrically above and below T(1). Noticeable change and hysteresis were also observed in the temperature dependence of the solubility coefficients. Diffusion of CO2 in the measophase is suggested from the permeation and sorption measurements. Gas transport parameters of CO2 in the mesophase are estimated, and the contributions of the mesophase and the crystalline phase to gas transport are considered.
Effect of isopropylidene replacement on gas transport properties of polycarbonates
Authors: McHattie J. S. , Koros W. J. , Paul D. R.
Published: April 2003

The gas sorption and transport properties of a series of polycarbonates in which the isopropylidene unit of bisphenol A polycarbonate has been replaced with another molecular group are presented. Two new materials, bisphenol of norbornane polycarbonate (NBPC) and bisphenol Z polycarbonate (PCZ), are compared with several polymers which have been studied previously in this laboratory, including bisphenol A polycarbonate (PC), hexafluorobisphenol A polycarbonate (HFPC), and bisphenol of chloral polycarbonate (BCPC). The effect of molecular structure on chain mobility and chain packing is related to the gas transport properties. Dynamic mechanical thermal analysis and differential scanning calorimetry are used to judge chain mobility, while x‐ray diffraction and free volume calculations give information about chain packing. Permeability measurements were made for He, H2, O2, N2, CH4, and CO2 at 35°C over a range of pressures up to 20 atm. Sorption experiments were also done for N2, CH4, and CO2 under the same conditions. The permeability coefficients of these polymers rank in the order HFPC ≫ NBPC>PC>BCPC ≫ PCZ for all of the gases. With the exception of BCPC, this order correlates well with fractional free volume. The low gas permeability of BCPC is attributed to a polarity effect. In general, bulky and relatively immobile substituents, as in HFPC and NBPC, can yield improved separation characteristics. The polar group of BCPC and the flexible cyclohexyl substituent of PCZ result in relatively low gas permeability.
Application of the bendler–shlesinger generalization of the vogel equation to ion‐conducting polymers
Authors: Fontanella J. J. , Wintersgill M. C. , Coughlin C. S. , Mazaud P. , Greenbaum S. G.
Published: April 2003

Previously published audio frequency electrical conductivity results for ion‐conducting polymers have been reanalyzed in terms of the Bendler‐Shlesinger (BENSH) generalization of the Vogel equation. The materials studied include poly (propylene oxide) (PPO), amorphous poly (ethylene oxide) (PEO), poly (dimethylsiloxane‐ethylene oxide) (PDMS‐EO), and polyphosphazene (MEEP) ‐based material. The BENSH equation provides a better fit of both vacuum and high‐pressure data for PPO and PDMS‐EO than does the Vogel equation. For MEEP, for which the data are of a lower accuracy, and PEO, for which the data are over a narrower range of temperatures, the Vogel equation provides a better fit. However, for the most reliable data, a systematic difference between the VTF equation and the data is found, while the BENSH equation fits all portions of the data equally well. It is concluded that the BENSH equation, and hence the defect‐diffusion model, provides an excellent description of the electrical conductivity for ion‐conducting polymers.
Phase behavior of poly(ethylene oxide) and sulfonated polystyrene blends with and without solvent
Authors: Lee Sang Cheol , Lee Moo Sung , Jo Won Ho
Published: April 2003

The phase behavior of poly (ethylene oxide) (PEO) and poly(styrene‐co‐sodium sulfonated styrene) (SPS) blends has been examined as a function of copolymer composition. The mixtures show complex coacervation in dilute benzene/methanol (9/1, v/v) solution. The presence of intermolecular interactions between PEO and SPS in solution is verified by viscometry. Interaction between PEO and SPS in the solid state was supported by small‐angle x‐ray scattering; however, binary blends containing low PEO content show high miscibility, whereas the blends with high PEO content show phase separation.
Studies of structure formation in grafting of polyacrylonitrile to polycaproamide fibers
Authors: Bogoeva‐Catseva G. , Pimonenko N. Yu. , Gabrielyan G. A. , Fazlyev F. A. , Gal'Braikh L. S.
Published: April 2003

The relationship between the basic structure parameters of a polycaproamide (PCA) substrate and the structure of grafted polyacrylonitrile (PAN) was studied. The influence of the total degree of crystallinity of the PCA fiber, its crystal modification, and the orientation of crystallites on the PAN structure in the copolymer were analyzed. The structure of PCA‐PAN graft copolymers was studied by infrared spectroscopy (dichroism and ATR), X‐ray structure analysis, nuclear magnetic resonance, and scanning electron microscopy. The development of an oriented isotactic structure was found in PAN grafted to a PCA substrate having a bigh degree of orientation. The type of crystal modification of PCA does not affect the structure formation process in PAN. The oriented structures in PAN arise directly in the course of synthesis rather than on the subsequent rearrangement of the molecular chains under the action of orientation drawing. In contrast to earlier findings, our studies indicate that synthesis under the conditions specified increases the degree of crystallinity of PCA and crystallite size. The grafted PAN chains are presumed to grow epitaxially under the influence of PCA crystallites.
Effect of diblock copolymers on dynamic mechanical properties of polyethylene/polystyrene blends
Authors: Brahimi B. , Ait‐Kadi A. , Ajji A. , Fayt R.
Published: April 2003

A systematic investigation of the dynamic mechanical properties of high‐density polyethylene (HDPE)/high‐impact polystyrene (HIPS)/copolymer blends was carried out. Blends of 80/20 weight percent of HDPE/HIPS were prepared in the melt state at 180°C in a batch mixer. Synthesized pure diblock (H77) and tapered diblock (H35) copolymers of hydrogenated polybutadiene (HPB) and polystyrene (PS) were added at different concentrations (1, 3, and 5 wt %), and the dynamic mechanical properties were investigated. The results show that: (1) both the tapered and the pure diblock copolymers enhance the phase dispersion and the interphase interactions; (2) structure and molecular weight are both important parameters in the molecular design of copolymers; (3) important effects occur when only small amounts of copolymer are added (up to the interface saturation concentration SC); (4) a micellar structure formation is possible when the copolymer is in excess in the blend; (5) the effect of the copolymer structure on the SC and the critical micellar concentration (CMC) is more pronounced than the effect of molecular weight. These concentrations are found to be lower for the tapered diblock copolymer. The analysis of the dynamic mechanical thermal analysis (DMTA) results obtained for the 20/80 HDPE/HIPS blend leads to the conclusion that the copolymers also enhance the interactions between heterogeneous phases. Similar conclusions based on electron microscopy were reported in the literature. DMTA shows great potential to relate macroscopic observations to the state of a copolymer in an immiscible blend.
Interaction of CO2 gas with silicone elastomer at high ambient pressures
Authors: Briscoe B. J. , Zakaria S.
Published: April 2003

Interaction of high‐pressure CO2 gas with a silicone elastomer, and to a lesser extent, with a nitrile rubber and a PTFE have been investigated. Sorptive dilations of the polymers were measured with the help of custom‐made piezoelectric ultrasonic transducers under gas pressures of up to ca. 22 MPa at 42°C. The gas mass sorption was determined by a vibrating reed probe. For the silicone elastomer system the dilation isotherm mimics the sorption isotherm. The partial molar volume (PMV) of the absorbed CO2 gas in the silicone elastomer has been computed. A significant drop in the PMV value is observed when the CO2 gas becomes supercritical. In the transition region, the transmission of ultrasonic signals through the specimen indicated the formation of discrete small (estimated as about 60 μm in diameter) high density zones of CO2 in the rubber matrix. The plasticization effects of the absorbed high pressure CO2 gas have been identified from the interpretation of the changes in the acoustic longitudinal modulus obtained from ultrasonic transmission measurements. The effects of rapid gas decompression on the structural integrity of the various polymers have also been determined. Significant inflation of certain specimens occur toward the latter stages of the decompression cycle. The initiation and development of internal cracks or bubbles was followed by monitoring the ultrasonic signal attenuation.
The gas permeability and packing density of copolymers of methacryloxypropyltris (trimethylsiloxy) silane and methylmethacrylate
Authors: Gu W. , Chern R. T. , Chen R. Y. S.
Published: April 2003

A series of random copolymers of methylmethacrylate and methacryloxypropyltris (trimethylsiloxy) silane were synthesized by free radical polymerization under ultraviolet light. The permeabilities of these copolymers to carbon dioxide, oxygen, and nitrogen were determined and correlated with the packing densities of the polymers. Correlation between the permeability and permselectivity of these copolymers is also addressed.
An NMR study of the electron beam‐induced polymerization of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate
Authors: Harrell J. W. , Choudhury Mubinur , Ahuja Sanjay , Walker William
Published: April 2003

Electron beam‐induced polymerization of trimethylolpropane triacrylate (TMPTA) and its methacrylate analog (TMPTMA) was studied using nuclear magnetic resonance (NMR) relaxation time measurements. Free induction decays (FID) of partially polymerized samples consist of a short Gaussian component and a longer component comprised of a distribution of simple exponentials. The relative intensity of the Gaussian component increases with radiation dose. T1 and T1ρ values were measured as a function of temperature and radiation dose. The relaxation is due primarily to methyl group reorientation at low temperatures, ethyl group reorientation at intermediate temperatures, and whole‐molecule reorientation at high temperatures. In both compounds, the T1 and T1ρ values at the high temperature minima increase with increasing dose, and the minima values can be used to estimate the degree of polymerization. The temperature at which the T1ρ minimum occurs increases with dose, suggesting an increase in the glass transition temperature, Tg, with polymerization. The polymerization appears to have very little effect on the low temperature CH3 reorientation in TMPTA. In TMPTMA the polymerization appears to reduce the mobility of the methacrylate methyl groups.
An analytical technique for measuring relative tie‐molecule concentration in polyethylene
Authors: Lustiger A. , Ishikawa N.
Published: April 2003

While consideration of the crystalline domains have long dominated research in understanding the properties of semicrystalline polymers, a satisfactory understanding of crack growth in these materials can only be realized by developing corresponding analytical tools to characterize the amorphous region. Since slow stable cracks in these materials preferentially form between crystalline lamellae, the role of tie molecules—the amorphous chains that bridge crystalline lamellae—are particularly important in this regard. Unfortunately, there is no method readily available for quantitative assessment of tie molecules. Through deformation and subsequent chlorination of polyethylene films, it is demonstrated that infrared dichroism can be used to determine relative tie‐molecule concentration. Using this technique, one can a priori predict which resin in a series having comparable densities but widely varying molecular weights or comonomer distributions exhibits better crack resistance.
Thermoacoustic measurements during cure of epoxy resin at room temperature
Authors: Yoon Hyoung No , Yoon Chang No , Kim Ho Chul
Published: April 2003

Dynamic thermoacoustic measurements were used to observe the curing of epoxy resin. Measurements were made at the modulation frequency (20 Hz) as a function of time. A two‐step increase of the thermoacoustic signal output was notable and could be explained in terms of the transitions liquid → rubber → glass.
The reaction of phenylpropylsilsesquioxane in the fiber spinning regime
Authors: Ishida H. , Shick R. , Hurwitz F.
Published: April 2003

A potential ceramic precursor, a phenylpropylsilsesquioxane co‐oligomer from Petrarch Systems (Petpps), was studied under conditions where fiber spinning is performed. The reaction kinetics of residual silanols of Petpps are studied using Fourier transform infrared spectroscopy in the temperature range 100–150°C. The activation energy and the reaction order of the silanol condensation reaction in the molten Petpps are determined. A combination of gel permeation chromatography, liquid chromatography, and nuclear magnetic resonance spectroscopy is used to study the possibility of copolymerization between the phenyl and propyl silane moieties.
Miscibility behavior and reequilibration of binary poly(amic acid) mixtures
Authors: Ree M. , Yoon D. Y. , Volksen W.
Published: April 2003

Five poly (amic acid) solutions based on PMDA‐PDA, PMDA‐ODA, PMDA‐6F, ODPA‐ODA, and 6FDA‐ODA were prepared in N‐methylpyrrolidone at a polymer concentration of ca. 10 wt %. From these five poly (amic acid) solutions, six different binary blends were prepared: PMDA‐PDA/PMDA‐ODA, PMDA‐PDA/PMDA‐6F, PMDA‐ODA/6FDA‐ODA, PMDA‐ODA/ODPA‐ODA, PMDA‐PDA/ODPA‐ODA, and PMDA‐PDA/6FDA‐ODA. These blends were then characterized with respect to miscibility in the ternary state (polyamic acid‐1/polyamic acid‐2/N‐methylpyrrolidone), the condensed state (ca. 70 wt % polymer), and the fully imidized state. All blends except for PMDA‐PDA/PMDA‐6F yielded homogeneous mixtures in the ternary solution of 10 wt % polymer concentration. The PMDA‐PDA/PMDA‐6F mixture eventually became homogeneous after 10 days of mixing at room temperature. Upon solvent evaporation (condensed state) and full cure (imidized state) two blends incorporating ODPA‐ODA as one of the components exhibited apparent miscibility as evidenced by optical microscopy. The remaining blends exhibited large‐scale phase separation upon solvent evaporation with no significant differences in the overall morphology between the condensed and imidized state. However, as in the case of the PMDA‐PDA/PMDA‐6F ternary system, the morphology in the condensed and imidized state was strongly dependent on the mixing time of the precursor poly(amic acid) components; the phase‐separated domain size decreased with increasing mixing time, eventually leading to complete miscibility. These results are discussed with respect to the proposed “polymer‐monomer” reequilibration reaction as well as its implications with respect to the preparation of polyimide molecular composites.
Surface orientation of a liquid‐crystalline polymer studied by polarized reflection spectroscopy
Authors: Kaito Akira , Nakayama Kazuo , Kyotani Mutsumasa
Published: April 2003

The polarized reflection spectrum was used to evaluate the surface orientation of extruded sheets of liquid‐crystalline copolyester consisting of 73 mol % 4‐hydroxybenzoic acid units and 27 mol % 2‐hydroxy‐6‐naphthoic acid units. The anisotropy of absorption index was evaluated from the specular reflectance using the Fresnel equation and the Kramers‐Kronig relation. An intense absorption and observed in the ultraviolet region was assigned to the π* ←π transitions of the constituent monomeric units. The observed spectra of the liquidcrystalline polymer were successfully interpreted by use of the spectroscopic data on the monomers. The transition moment directions of the monomeric units were calculated by molecular orbital calculations within the framework of the CNDO/S‐Cl approximation. The Surface orientation functions obtained from polarized reflection spectra were compared with the crystal orientation functions in the bulk, which were obtained from the azimuthal intensity distribution of wide‐angle x‐ray diffraction. The orientation behaviour at the surface of the liquid‐crystalline polymer was shown to be equivalent to the orientation behaviour in the bulk at higher draw‐down ratio.
Structure and properties of sequentially polymerized propylene‐b‐[ethylene‐co‐propylene]‐b‐propylene copolymers
Authors: Wang Lixiao , Huang Baotong
Published: April 2003

The structure and properties of presumed block copolymers of polypropylene (PP) with ethylene‐propylene random copolymers (EPR), i.e., PP‐EPR and PP‐EPR‐PP, have been investigated by viscometry, transmission electron microscopy, dynamic mechanical analysis, differential scanning calorimetry, gel permeation chromatography, wide‐angle x‐ray diffraction, and other techniques testing various mechanical properties. PP‐EPR and PP‐EPR‐PP were synthesized using δ‐TiCl3‐Et2‐AlCl as a catalyst system. The results indicate that the intrinisic viscosity of these polymers increases with each block‐building step, whereas the intrinsic viscosity of those prepared by chain transfer reaction (strong chain‐transfer reagent hydrogen was introduced between block‐building steps during polymerization) hardly changes with the reaction time. Compared with PP/EPR blends, PP‐EPR‐PP block copolymers have lower PP and polyethylene crystallinity, and lower melting and crystallization temperatures of crystalline EPR. Two relaxation peaks of PP and EPR appear in the dynamic spectra of blends. They merge into a very broad relaxation peak with block sequence products of the same composition, indicating good compatibility between PP and EPR in the presence of block copolymers. Varying the PP and EPR content affects the crystallinity, density, and morphological structure of the products, which in turn affects the tensile strength and elongation at break. Because of their superior mechanical properties, sequential polymerization products containing PP‐EPR and PP‐EPR‐PP block copolymers may have potential as compatibilizing agents for isotactic polypropylene and polyethylene blends or as potential heat‐resistant thermoplastic elastomers.
Methanol‐induced opacity in poly (methyl methacrylate)
Authors: Lin C. B. , Liu K. S. , Lee Sanboh
Published: April 2003

Methanol‐induced opacity in poly (methyl methacrylate) (PMMA) is investigated subject to two cooling processes; furnace cooling and air cooling. The glass transition temperature of PMMA decreases with increasing time of exposure to methanol at 40–60°C and then increases during cooling, due to progressive desorption. Voids form during cooling as long as specimen temperature remains above its glass transition temperature. Since furnace cooling affords enough time for holes to expand larger than the light wavelengths, the transmittance of furnace‐cooled PMMA is independent of wavelength. The transmittance of PMMA subjected to rapid cooling in the air is wavelength dependent due to scattering by holes smaller than light wavelengths. The transmittance of PMMA bearing a given weight gain of methanol (measured at absorption temperature) prior to cooling for furance cooling is lower than that for the same material subjected to air cooling. A sharp front between outer and inner regions is found in specimens removed quickly from the thermostated water bath to air at ambient temperature.
Gelation of poly(n‐butylisocyanate) in benzene
Authors: Olayo Roberto , Miller Wilmer G.
Published: April 2003

Poly (n‐butylisocyanate)‐benzene solutions prepared by solubilization at 45°C, followed by aging at room temperature were found to be metastable for months, although, eventually, they separated into a birefringent polymer‐rich phase and an isotropic solution. These metastable solutions, as well as isothermally phase‐separated biphasic samples, flowed and exhibited dynamic moduli indicative of low polymer connectivity. By contrast samples prepared by a freeze‐thaw cycle were uniformly and highly birefringent and showed network (gel) behavior at room temperature. The mechanism of gel formation is most likely the exclusion of the polymer from the benzene crystal during crystallization, forcing the polymer to align and exist at grain boundaries. Films formed from solutions have different moduli than those formed from gels, and are consistent with the proposed mechanism.
Some connections between viscoelastic properties of PVC and plasticized PVC and molecular kinetics
Authors: Ngai K. L. , Yee A. F.
Published: April 2003

A coupling model that has been shown in the past to be capable of relating macroscopically measured relaxation parameters to molecular ones has been presented. In this article the coupling model is applied to the analysis of stress relaxation data collected by Cama and Sternstein on PVC and plasticized PVC. The Kohlrausch‐Williams‐Watts form, exp — (t/τ*)1−n, using n = 0.77 is found to be capable of describing the stress relaxation master curve at temperatures below the glass transition, Tg. From the temperature‐independent apparent activation energy found by Cama and Sternstein, the primitive activation energy of the α‐relaxation was calculated to be 7.5 kcal/mol, which is a reasonable value for the energy barrier to internal rotational isomerism in PVC. Support for this value is found from the data on two plasticized PVCs with different Tgs and apparent activation energies. By applying the coupling model in a similar manner, the primitive activation energies were found to be 8.5 kcal/mol for PVC plasticized with 6 pph dioctylphthalate and 7.7 kcal/mol for PVC plasticized with 6 pph tricresyl phosphate. Within experimental uncertainties, the three primitive activation energies can be considered to be the same. This finding is consistent with the physical basis for primitive activation energy and its identification with the internal rotation barrier, which should be independent of the type and amount of plasticizer in the system. Analysis of Cama and Sternstein's data on the effect of repeated stress aging on stress relaxation of quenched samples of PVC and plasticized PVC show that the coupling constant n increases systematically with each successive stress‐aging cycle until it approaches the value for slow‐cooled samples. These results are consistent with the notion that stress‐aging changes the structural state of the glass in ways similar to physical aging.
The absorption of organic liquids in poly(aryl‐ether‐ether‐ketone) [PEEK]
Authors: Wolf Clarence J. , Bornmann John A. , Grayson Michael A.
Published: April 2003

The absorption and subsequent desorption of benzene, toluene, carbon disulfide, and chloroform in amorphous and 27% crystalline poly (aryl‐ether‐ether‐ketone) (PEEK) were determined. At 35°C, the equilibrium weight gain (solubility) of benzene, toluene, chloroform, and CS2 are 23.5, 19.8, 51.2, and 21.2 wt%, respectively. The initial weight gain is linear with root‐time and pseudodiffusion constants for absorption into amorphous PEEK ranging from 0.35 to 9.85 x 10‐12m2/s were calculated. The desorption processes are two‐step and are controlled by the Tg of the penetrant‐resin mixture. The rate of diffussion into the crystalline material is extremely slow; crystalline PEEK reaches saturation (12.5 wt%) after immersion in CS2 (35°C) for several hundred hours but, even after 1300 h immersion, the other fluids do not reach saturation.
Transient behavior of entangled polymers at high shear rates
Authors: Pearson D. , Herbolzheimer E. , Grizzuti N. , Marrucci G.
Published: April 2003

A new model is presented for describing the time‐dependent flow of entangled polymer liquids at high shear rates. The results were obtained by extending the Doi and Edwards theory to include the effect of chain stretching. This nonlinear phenomenon is predicted to occur when the product of the shear rate and longitudinal relaxation time of the polymer exceeds one. If a constant‐shear‐rate flow is started under these conditions, it is shown that the shear stress and the normal stress are considerably larger than that predicted by the original reptation model. We also find that both of these stresses can pass through maxima before reaching a steady state and that the times required to reach these maxima are constants independent of the shear rate. In general the new model requires the numerical solution of coupled partial differential equations. However, at the highest shear rates where reptative relaxation is no longer important, an analytical solution for the stresses is found. The results obtained here are shown to agree well with experimental data and to be an improvement over a simpler model recently proposed.
Some further observations on the systems cellulose/trifluoroacetic acid/CH2Cl2 and cellulose triacetate/TFA/CH2Cl2
Authors: Hawkinson D. E. , Kohout E. , Fornes R. E. , Gilbert Richard D.
Published: April 2003

There is little or no trifluoroacetylation of cellulose dissolved in TFA‐CH2Cl2 admixtures. Both cellulose and cellulose triacetate (CTA)are slowly degraded in the solvent. Cellulose forms a mesophase as low as 4%(w/w)concentration, but CTA has a much higher critical concentration, 20% (w/w), in TFA‐CH2Cl2. The cellulose behaves as a rigid rod in TFA‐CH2Cl2 (70/30v/v) and its persistence length calculated using the lattice model approximates its chain length, presumably due to extensive interaction with the solvent. As expected, due to low polymer‐solvent interactions, the persistence length of CTA in TFA‐CH2Cl2 is only one‐fourth the chain length.
A novel staining technique for studying toughening mechanisms in saturated acrylic rubber‐modified polymers
Authors: Sue H. J. , Garcia‐Meitin E. I. , Burton B. L. , Garrison C. C.
Published: April 2003

A novel technique which utilizes a two‐stage staining approach, (i.e., styrene absorption followed by osmium tetraoxide staining) is introduced for staining saturated polyacrylate rubbers. This novel staining approach, which stains and hardens polyacrylate rubber, is found to be useful for room temperature microtomy of polyacrylate rubber‐modified polymers. Therefore, both the morphology and the crack tip toughening mechanisms of polyacrylate rubber‐modified systems can be studied. Details concerning staining time, staining media, and use of solvents are discussed.
Mass transfer coupled with the relaxation of a polymeric matrix: A controlled release process
Authors: Cooke Norman E.
Published: April 2003

A solution to Fick's equation is presented which accurately predicts the transfer of mass out of a polymeric rod or sheet undergoing relaxation by a solvent permeating it by Case II transport. There is a critical length. Before the solvent permeates to this length the diffusible material can diffuse away from the moving boundary faster than it is becoming available at the boundary. Afterward the reverse is true. Five sets of experimental data from three different sources have been used to test the model. The agreement is excellent.
On the rheology of cold drawing. II. Viscoelastic materials
Authors: Coleman Bernard D. , Newman Daniel C.
Published: April 2003

In this second paper in a series on cold drawing of polymeric fibers and films, asymptotic formulae are derived for the tension in thin bodies of nonlinearly viscoelastic materials subject to inhomogeneous stretching. The formulae, which are valid to within an error of fourth order in sample thickness, give the tension in fibers and films as functionals of the histories of the local stretch and its first two spatial gradients. It is shown that the theory obtained by taking the formulae to be exact is consistent with thermodynamical principles. Material response for various types of histories is discussed, and the theory is employed to calculate the creep response of fibers under static loads. Numerical solutions of the evolution equation for the stretch field in creep show that for an appropriate class of materials with slowly fading memory there is a range of applied loads for which an initially homogeneous deformation evolves into a well defined neck whose edges advance at high speed along the fiber and in so doing transform moderately stretched material into highly stretched (i.e., drawn) material. The calculated fiber profiles and the predicted dynamics of neck formation and growth are in good accord with familiar observations. A description is given of the circumstances under which one can use instantaneous (i.e., high speed) response functions to calculate fiber profiles in rapidly growing necks.
Miscibility and phase behavior in atactic polystyrene and poly(o‐chlorostyrene‐co‐p‐chlorostyrene) blends: Effect of polystyrene molecular weight and copolymer composition
Authors: Cimmino S. , Karasz F. E. , MacKnight W. J.
Published: April 2003

Miscibility in blends of random copolymers of o‐chlorostyrene and p‐chlorostyrene [P(oClSy‐co‐pClS1‐y)] with 8 atactic polystyrene (aPS) fractions has been studied at temperatures ranging from 150°C to 300°C. Miscibility windows whose size depends on the molecular weight of the PS and on the copolymer composition, y, were observed for each blend. From these data, the temperature dependence of the three segmental interaction parameters required to describe this system were obtained.
Nature of mechanoradical formation and reactivity with oxygen in methacrylic vinyl polymers
Authors: Kuzuya Masayuki , Kondo Shin‐Ichi , Noguchi Akihiro , Noda Nahoko
Published: April 2003

The formation of mechanoradicals under anaerobic conditions and their reactivity with oxygen at room temperature is described for several methacrylic vinyl polymers. Observed electron spin resonance (ESR) spectra of the mechanoradicals formed were all essentially identical and are clearly assigned to a respective endchain radical. The ESR kinetics of the mechanoradical formation of polymethylmethacrylate (PMMA) and polymethacrylamide (PMAAm) exhibit an interesting contrast; the progressive changes in the radical concentration in PMMA as a function of duration of milling gradually decrease after reaching a maximum value, while those of PMAAm show a parabolic increase. This discrepancy has been ascribed to mechanoradicals of PMAAm that are strongly stabilized by intermolecular and intramolecular doubly hydrogen‐bonded networks among the amide groups. Such interactions also are to lower the reactivity of the mechanoradicals with oxygen. Thus, the mechanoradicals of both PMAAm and PMAA do not give a single peroxy radical, but rather a mixture of the mechanoradical and peroxy radical even after exposure to air, while the mechanoradicals of other polymers are rapidly converted to the corresponding peroxy radicals. Such a difference was observed in experiments on the mechanical fracture of such polymers under aerobic conditions.
Permeation of binary gas mixture through glassy polymer membranes with concentration‐dependent diffusivities
Authors: Sada E. , Kumazawa H. , Wang J.‐S.
Published: April 2003

An analytical solution has been obtained for the modified dual‐mode mobility model for a single gas proposed by Zhou and Stern and extended to a binary gas mixture to describe the pressure dependence of mean permeability coefficients for CO2 and CH4 mixtures in homogeneous cellulose triacetate membranes. The permeabilities calculated from the model fitted the corresponding experimental results quite well. Permeation experiments for equimolar CO2 and CH4 mixture in a homogeneous membrane of methyl methacrylate and n‐sbutyl acrylate copolymer were performed along with sorption experiments for pure CO2 and CH4 to test the applicability of the model. The experimental permeabilities were close to those calculated from the model.
Absorption of toluene in poly(aryl‐ether‐ether‐ketone)
Authors: Wolf Clarence J. , Bornmann John A. , Grayson Michael A.
Published: April 2003

The absorption and swelling of poly(aryl‐ether‐ether‐ketone) (PEEK) in toluene as a function of resin morphology and temperature in the range 35–95°C was investigated. In all cases the weight gain curves exhibit three characteristics: (1) an induction period, which is a strong function of both temperature and initial crystallinity, (2) a main absorption region, which is linear with square‐root time, and (3) a final equilibrium value, namely, solubility. The solubility of amorphous PEEK decreases with temperature and the heat of solution is −0.93 kcal/mol. The induction period varies with the fourth power of the crystallinity and decreases with temperature with an apparent activation energy of 50 kcal/mol. The strength of the interaction between the crystalline regions is markedly reduced at temperatures greater than 80°C. Swelling accompanying the absorption of the toluene is highly anisotropic with most of the dimensional changes occurring in the thickness direction. The deswelling process, however, is essentially isotropic. The concentration of toluene in solution has a strong effect on the transport process; the equilibrium solubility of toluene in amorphous PEEK immersed in a toluene/iso‐octane mixture is a linear function of toluene concentration; but the pseudo‐diffusion coefficient for the absorption of toluene varies approximately with the fourth power of its concentration.
Diffusion in glassy polymers: A model using a homogenization method and the effective medium theory
Authors: Horas Jorge A. , Toso Juan P.
Published: April 2003

Glassy polymers are considered as inhomogeneous with regions in which the gas sorption follows Henry's law and others where it follows Langmuir's law. It is assumed that the linear dimensions of these regions are small compared with the macroscopic length of interest but large compared with the mean free path of the penetrant gas molecules. Applying an homogenization method it is shown that the average flux is directly proportional to the concentration gradient in the polymer. This relationship can be expressed in terms of an effective diffusion coefficient Deff, which depends on the details of the microstructure. Deff is evaluated in the framework of the effective medium theory and compared with experimental data for diffusion of five vapors in ethylcellulose.
The evolution of steep fronts in non‐fickian polymer‐penetrant systems
Authors: Hayes Catherine K. , Cohen Donald S.
Published: April 2003

We adapt a recently proposed model for non‐Fickian diffusion of penetrants into polymers and use it to study a drug‐delivery problem. The model modified Fick's diffusion equation by the addition of stress‐induced flux. A stress evolution equation incorporating aspects of the Maxwell and Kelvin‐Voigt viscoelastic stress models completes the model. The relaxation time in the polymer is taken as a function of the penetrant concentration. The system is studied under the assumption that the diffusivity is large. Singular perturbation techniques are used to show that the concentration and stress evolve diffusively for small time, but exhibit steep fronts in a narrow region within the domain for larger time. These predictions are verified numerically for specified parameter values. Finally, the equations are studied in the steady state and are found to predict the evolution of shocks.
Chain fragmentation under liquid‐state and solid‐state conditions
Authors: Hellmann E. H. , Kuhn K. J. , Hellmann G. P. , Rennie A. R.
Published: April 2003

Thermally Activated fragmentation of copolycarbonates PC(TxA1‐x) of bisphenol A (unit CA) and the Heat‐sensitive diol 1,1,2,2‐tetraethyl‐1,2‐di‐(p‐hydroxy) phenylethane (unit CT) was studied in the bulk, i.e., in the pure copolymers and in their blends with the polycarbonates of bisphenol A (PCA) or tetramethyl bisphenol A (TMPC). Fragmentation proceeds via dissociation followed by disproportionation at the central CC bond of the unit CT. The reaction has rates that are convenient to study near the glass transition temperature. The “chemical” time constants τ for the entire reaction and τ2 for the disproportionation step compete with the “physical” time constants δα for segmental motion and δq for fragment diffusion. A cage effect is observed below τ2 = δα and effects of delayed matrix response below τ = δα and τ = δq. Owing to the two latter effects, parameters such as the glass transition temperature and the structure factor of concentration fluctuations do not respond primarily to the fragmentation, but rather to subsequent relaxation and diffusion processes in the polymer matrix.
Liquid‐crystalline ordering in polymeric networks as studied by polarized raman scattering
Authors: Heynderickx I. , Broer D. J. , Van Den Boom H. , Teesselink W. J. D.
Published: April 2003

Uniaxially oriented polymer networks are produced by photoinitiated bulk polymerization of liquid‐crystalline diacrylates. The order parameters S2 and S4 of the mesogenic moieties in these networks are simultaneously determined by means of the polarized Raman scattering technique. It yields an estimate of the orientation distribution function for different polymerization temperatures and for different lengths of the alkyl chain, present as a spacer in the liquid‐crystalline diacrylate.
Dielectric relaxation of poly(phenylene sulfide) containing a fraction of rigid amorphous phase
Authors: Huo Pengtao , Cebe Peggy
Published: April 2003

The dielectric relaxation behavior of poly(phenylene sulfide), PPS, has been investigated from room temperature to 180°C. This study was undertaken to examine the mobility of the amorphous phase through the glass transition region, to determine the contribution that rigid amorphous phase material makes to the relaxation process. Semicrystalline samples contain a fraction of the rigid amorphous phase, which was determined from the heat capacity increment at the glass transition, using degree of crystallinity determined from x‐ray scattering. In the dielectric experiment, we measured the temperature and frequency dependence of the real and imaginary parts of the dielectric function. ε″ vs. ε′ was used to determine the dielectric relaxation intensity, δε = εs–ε∞, at temperatures above the glass transition. For amorphous PPS, δε decreases as temperature increases, while for all semicrystalline PPS, δε increases with temperature. The ratio of semicrystalline intensity to amorphous intensity determines the total fraction of dipoles which are already relaxed at a given temperature. Results indicate that more and more rigid amorphous phase material relaxes as the temperature is increased. This provides the first evidence that rigid amorphous phase material in PPS contains chains that possess different levels of molecular mobility. Finally, to the temperature of the loss peak maximum, at a given frequency, we assign the value of the dielectric Tg. For both melt and cold crystallization, the dielectric Tg systematically decreases as the crystallization temperature increases, and as the fraction of rigid amorphous phase decreases.
Solvent‐induced crystallinity in poly(aryl‐ether‐ether‐ketone) [PEEK]
Authors: Wolf Clarence J. , Bornmann John A. , Grayson Michael A. , Anderson David P.
Published: April 2003

The amount and structure of the crystals formed by the solvent‐induced crystallization (SIC) following a sorption‐desorption cycle of five fluids (benzene, toluene, chloroform, methylene chloride, and carbon disulfide) in amorphous PEEK was determined by wideangle x‐ray scattering (WAXS). The SIC crystal structure was compared with that produced by thermal methods, both those formed at low temperature by heating the amorphous material 10–20°C above Tg or by cooling from the melt. Although smaller in size, the SIC crystals are tighter and more organized than those produced thermally. The WAXS data indicates that all five fluids produce approximately 35% crystallinity in PEEK. Gravimetric data suggest that a low‐density region, consisting of either microvoids or highly disordered amorphous region, surrounds the crystals.
The effect of heating on polyaniline powders studied by real‐time synchrotron radiation diffraction, mass spectrometry and thermal analysis
Authors: Boyle A. , Penneau J. F. , Geniès E. , Riekel C.
Published: April 2003

The effect of heating on four chemically synthesized polyanilines, three of which were doped by HCI, H2SO4, HCIO4, and one sample which was dedoped, was investigated. The structural variations during thermal decomposition were studied by real‐time synchrotron radiation diffractometry and correlated with mass spectrometry (MS), thermal gravimetry (TG), and differential thermal analysis (DTA). These macroscopic and microscopic techniques were combined in order to shed more light on the role played by the water and the counteranion molecules on the structure of doped polyaniline. Evidence for two H2O fractions was found for HCI‐doped polyaniline. Chain degradation was observed for HCIO4 and H2SO4‐doped polyaniline. The results indicate that intermediate sulphonation of polymer chains occurs in the latter case.
Valence band x‐ray photoelectron spectroscopy of poly(ether ketone) and poly(ether‐ether ketone)
Authors: Cain Stephen R. , Matienzo Luis J.
Published: April 2003

Poly(ether ketone) and poly(ether‐ether ketone) are characterized by valence band x‐ray photoelectron spectroscopy. The valence band region appears to be resolved into six regions. Peak assignments were made by comparing the observed spectra with simulations from extended Hückel type band calculations. Results of the band calculations agreed fairly well with the experimental data.
Crystal structure of poly(p‐phenylene) prepared by organometallic technique
Authors: Sasaki S. , Yamamoto T. , Kanbara T. , Morita A. , Yamamoto T.
Published: April 2003

The two‐dimensional crystal structure of poly(p‐phenylene) is investigated by linkedatom Rietveld analysis of the x‐ray diffraction powder profile. Two molecular chains are packed in a rectangular pgg unit cell (a = 0.779 nm; b = 0.551 nm) with a paracrystalline shift distortion along the chain axis. The molecular conformation is not rigidly planar; rotations between adjacent phenyl‐ring planes in a molecule alternate with an angle of about 20°. The setting angle between the mean molecular plane and the a axis is 55.5°.
Crystal and molecular deformation in strained high‐performance polyethylene fibers studied by wide‐angle x‐ray scattering and Raman spectroscopy
Authors: Moonen Joost A. H. M. , Roovers William A. C. , Meier Robert J. , Kip Bert J.
Published: April 2003

Wide‐angle x‐ray scattering (WAXS) and Raman spectroscopic data show that on both the crystal and molecular levels, a bimodal stress distribution exists in strained high‐performance polyethylene fibers. In part of the crystalline PE the microscopic strain level is high (ca. 70% of macroscopic strain); in the remainder, the microscopic strain level is low (independent of macroscopic strain, ca. 0.4%). During stress relaxation the fraction of highly strained PE decreases with time. WAXS revealed no indication of a change in the a and b unit‐cell dimensions. Furthermore, no indications for stress‐induced formation of monoclinic and/or hexagonal PE and for crystal breaking were found. From the latter it can be deduced that all chains within one crystal are equally strained. The WAXS results are used to calibrate the stress‐induced frequency shifts of Raman bands.