bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and properties of sequentially polymerized propylene‐b‐[ethylene‐co‐propylene]‐b‐propylene copolymers
Authors: Wang Lixiao , Huang Baotong 
Published: April 2003

AbstractThe 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

AbstractMethanol‐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

AbstractPoly (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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractThere 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

AbstractA 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

AbstractA 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

AbstractIn 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

AbstractMiscibility 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

AbstractThe 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

AbstractAn 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

AbstractThe 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

AbstractGlassy 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

AbstractWe 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

AbstractThermally 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

AbstractUniaxially 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

AbstractThe 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

AbstractThe 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.