bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystal stability and mechanical properties of drawn polymers: A statistical‐mechanical approach
Authors: Itoyama Kuniyoshi 
Published: April 2003

AbstractThe partition function is formulated by the generating function method for a stacked lamellar model of alternating crystalline and amorphous layers. The random‐walk problem of enumerating statistical weights for conformations of amorphous chains confined by two parallel walls is solved for the body‐centered cubic lattice as a generalization of the one‐wall model treated by Roe. The mean lengths of loop, tie, and cilia chains and the free energy of the system are calculated for the random‐reentry and‐bridge model as a function of the distance h of separation between crystal layers and as a function of the number N of loop chains in a crystal block as the basic structural element of the system. The mean length of amorphous chains decreases at a given thickness l of the crystal layers with decreasing h or with increasing N. The free energy of the system exhibits no minimum with respect to N, showing that the folded‐chain crystal is thermodynamically stable, especially for relatively small l. Additionally, it is shown that another requirement for stabilizing relatively small crystals (small l) is the formation of an aggregate structure of crystals, whereas a large single‐crystal (large l) is relatively stable, irrespective of h and N. Furthermore, a theoretical model is developed to calculate the force and elastic modulus of a highly deformed stacked system, assuming that the only change in the configurations of amorphous chains within the interlamellar regions is due to deformation, except for scission of tie chains having fewer segments than are needed to span the interlamellar distance of the deformed system. It becomes evident that taut tie chains are effective in increasing the modulus of the stacked system.
Brillouin scattering studies of the effect of orientation on mechanically deformed poly(ethylene terephthalate)
Authors: Cavanaugh David B. , Wang C. H. 
Published: April 2003

AbstractBrillouin scattering is used to study the internal structure of oriented films of poly(ethylene terephthalate). Splitting in the longitudinal spectrum is observed as the film is stretched, indicating that the crystalline region is developed gradually from the amorphous region. The hypersonic velocity data obtained from these two regions are used to draw directional maps of sound velocity propagation in different directions of the film. The results are discussed and correlated with a recently proposed model. The orientational parameter in the amorphous phase is calculated from the hypersonic velocity data as a function of stretch ratio. The results are found to be in good agreement with published values obtained by a different technique.
Gas sorption and transport in a copolyester and its blend with polycarbonate
Authors: Masi P. , Paul D. R. , Barlow J. W. 
Published: April 2003

AbstractSorption and transport measurements for various gases were made with a copolyester formed from 1,4‐cyclohexanedimethanol and a mixture of terephthalic and isophthalic acids. Similar observations for the miscible blends of this copolyester with polycarbonate were made using carbon dioxide. All of these results are described well by dual sorption‐dual mobility models which have been used effectively for other gas‐glassy polymer systems. The sorption and transport parameters deduced experimentally from these systems have been correlated and interpreted in terms of applicable theories. For the blends, the Henry's‐law sorption parameter has been used to deduce a reasonable value of the interaction parameter for the polycarbonate‐copolyester blend system from the Flory‐Huggins theory of mixtures. The Langmuir capacity term from the dual‐sorption model is accurately related to the unrelaxed volume of the glass. Negative deviations of permeability and diffusion coefficients from simple additivity relations were observed and qualitatively interpreted to result from the decrease in volume on mixing for the blends.
The effect of aging on the thermal behavior of sulfonated polystyrene
Authors: Weiss R. A. 
Published: April 2003

AbstractThe thermal properties of an ionomer glass, lightly sulfonated polystyrene, was studied as a function of aging at room temperature after being cooled from the melt. An anomalous endothermic event below Tg was observed by differential scanning calorimetry; the intensity of this excess enthalpy was a function of time and sulfonate concentration. It is suggested that the origin of this relaxation may be due in part to morphological changes that occur as a consequence of electrostatic interactions of the sulfonate groups.
Behavior of concentrated polystyrene solutions in large‐amplitude oscillating shear fields
Authors: Pearson Dale S. , Rochefort Willie E. 
Published: April 2003

AbstractThe limits of linear viscoelastic behavior of polystyrene solutions have been investigated by subjecting them to large‐amplitude oscillatory strains, γ0. At strains less than one we find that the dynamic storage modulus G′(ω,γ0) and the dynamic loss modulus G″(ω,γ0) decrease quadratically with increasing strain. As a measure of the size of the linear viscoelastic region, we have determined the strain at which the moduli have fallen 5% below their zero‐strain values. This strain, γNL, is found to be independent of frequency ω at high frequencies but to increase with decreasing frequency at low frequencies. Behavior of this type is in qualitative agreement with the recent constitutive equation developed by Doi and Edwards. More specifically, we find that the rate of decrease of the storage modulus with increasing strain is quite similar to that predicted by their theory, but that the rate of decrease of the loss modulus is much slower. Some possible approaches for improving the agreement with experimental results are suggested. In the course of our work an interesting hydrodynamic instability was observed. The nature of this instability and methods to avoid it are discussed.
Phase separation in perfluorosulfonate ionomer membranes
Authors: Roche E. J. , Pineri M. , Duplessix R. 
Published: April 2003

AbstractThe extent of phase separation in Nafion® perfluorosulfonate ionomer membranes has been studied by small‐angle neutron scattering (SANS). These polymers, which consist of a perfluorocarbon main chain and a sulfonate‐containing side group, can absorb up to 30% by weight of water. Previous studies have shown that clustering of water occurs, forming particles in the size range observable by SANS. The current study is concerned with the fraction of water molecules which participate in the clustering and the chemical composition of the phases present. Experiments have been made on melt‐quenched samples which have no fluorocarbon crystallinity. The analysis is based on isotopic replacement experiments in which SANS measurements are made on samples hydrated with mixtures of H2O and D2O. Values of the small‐angle x‐ray scattering (SAXS), mean‐square electron density fluctuation, and mass density are used as additional criteria. It is shown that at high water content (more than 15% absorption by weight), a two‐phase model can explain the data with a majority (>60%) of the water molecules in one phase and most (>90%) of the perfluorocarbon in the other phase; a sample hydrated to a lower extent (8% by weight) shows deviations from the two‐phase model. These results are consistent with the scattering behavior at large angles observed by SAXS.
Poly(P‐phenylene sulfide) hexafluoroarsenate: A novel conducting polymer
Authors: Clarke T. C. , Kanazawa K. K. , Lee V. Y. , Rabolt J. F. , Reynolds J. R. , Street G. B. 
Published: April 2003

AbstractPoly(p‐phenylene sulfide) (PPS) is a melt‐ and solution‐processible polymer which on treatment with AsF5 forms a blue‐black material with a conductivity of 1–10 Ω−1 cm−1. Thermopower measurements indicate that the resulting polymer is p type, consistent with partial oxidation of the PPS by the AsF5. The rate and extent of this doping process prove to be particularly sensitive to the degree of crystallinity of the starting polymer. There is also evidence of crosslinking of the polymer chains during the reaction with AsF5. The details of both the chemistry and physics of the doping of PPS and several of its derivatives are presented.
Effects of thermal history, crystallinity, and solvent on the transitions and relaxations in poly(bisphenol‐A carbonate)
Authors: Varadarajan K. , Boyer Raymond F. 
Published: April 2003

AbstractThe following system of nomenclature for the transitions and relaxations in polycarbonate has been proposed: α = Tg = 150, β = 70, γ = −100, and δ = −220°C (frequency range of 10–50 Hz). The three component peaks of the γ relaxation are denoted by γ1, γ2, and γ3 relaxations correspond to phenylene, coupled phenylene‐carbonate, and carbonate motions, respectively. Dynamic mechanical analysis of poly(bisphenol‐A carbonate) using the DuPont 981–990 DMA system shows that the magnitude of the β relaxation depends upon the thermal history of the polycarbonate; annealing greatly reduces the intensity of the β relaxation. A relaxation map constructed for the β relaxation gives an activation energy of 46 kcal/mol. Exposure of polycarbonate to methylene chloride vapor for various times shows that after an induction period of about 5 min the intensity of the γ3 relaxation at −78°C decreases whereas the intensity of the γ1 relaxation of −30°C is unaffected and the ratio E″(γ1)/E″(γ3) increases linearly with the square root of time. This has been ascribed to the interaction of methylene chloride on the carbonate group in polycarbonate. Thermal crystallization of polycarbonate does not affect the positions of the γ relaxation and the glass transition peaks, but merely reduces their intensity. The glass transition peak intensity falls off sharply in comparison to the γ relaxation intensity. Both the γ3 and γ1 peaks in polycarbonate have been observed simultaneously for the first time by dynamic mechanical analysis. Impact strength measurements show that methylene chloride treatment of polycarbonate results in a change in mode of failure from ductile to brittle with a resultant 40‐fold reduction in impact energy for fracture. Thermally crystallized polycarbonate exhibits brittle fracture with very low force and energy at break.
Static and dynamic scattering behavior of regularly branched chains: A model of soft‐sphere microgels
Authors: Burchard Walther , Kajiwara Kanji , Nerger Dittmar 
Published: April 2003

AbstractThe static structure factor and the first cumulant of the time correlation function in dynamic light scattering have been calculated for a regularly branched molecule with n shells of branching generations which are connected by chains of m repeating units per chain. Ideal flexibility for the chains is assumed. The dynamic scattering functions of these soft spheres show behavior significantly different from that of a hard sphere. The theory describes very satisfactorily the static and dynamic light scattering results obtained experimentally with polyvinyl acetate microgels. The possibility of determining the glass transition temperature of latex particles is briefly discussed.
The influence of draw‐induced structural changes on the activity of a semicrystalline polymer‐supported catalyst
Authors: Cooper C. A. , Gates B. C. , McCullough R. L. , Seferis J. C. 
Published: April 2003

AbstractThe activity of a solid, polymer‐supported catalyst (a semicrystalline polyethylene film containing grafted, sulfonated styrene) was shown to be altered by cold drawing. The catalytic activity was measured by a test reaction, the dehydration of isopropyl alcohol to give propylene. Catalytic reaction rates were measured with variously drawn films clamped in a differential flow reactor operated at 100°C and 1 atm. The catalytic activity increased with the elongation of the polymer up to a draw ratio of 2.5; the activity decreased upon further drawing. The drawn films were characterized by x‐ray diffraction, dynamic mechanical measurements, electron microscopy, birefringence, and density measurements. Since no evidence was found for the formation of surface sites by creation of microcracks, the changes in activity are attributed to modifications in the polymer structure induced by drawing. The kinetics of the catalytic reaction and the data giving percentage crystallinity and crystalline and amorphous orientation factors suggest that, in the undrawn polymer, the catalytically active SO3H groups form a hydrogen‐bonded network, which is excluded from the crystalline regions. Initial elongation partially breaks up the network, allowing more SO3H groups to bond to alcohol and become catalytically engaged. Elongation beyond a draw ratio of 2.5 leads to a separation of SO3H groups greater than that required for the formation of the reaction intermediate, which involves the alcohol hydrogen bonded to several SO3H groups. The combined results of the catalytic kinetics experiments and structural characterizations imply that the preliminary deformation response of the semicrystalline polymer occurs predominantly within the noncrystalline regions and is accommodated by the rigid slip and tilting of crystal lamellae. The hydrogen bonding among the SO3H groups in the noncrystalline regions hinders lamellar breakup and suppresses the formation of highly aligned fibrillar morphologies.
Elastic modulus of crystalline regions of poly(butylene terephthalate) in the direction parallel to the chain axis
Authors: Nakamae Katsuhiko , Kameyama Masao , Yoshikawa Motoyoshi , Matsumoto Tsunetaka 
Published: April 2003

AbstractThe elastic modulus El of crystalline regions of poly(butylene terephthalate) in the direction parallel to the chain axis has been measured by the x‐ray diffraction method. Values of El for the (104) planes of the α‐ and β‐form crystal modifications were 13.5 X 104 and 21.0 X 104 kg/cm2, respectively. These values of El are very low compared with that of polyethylene terephthalate (110 X 104 kg/cm2). The results are discussed in terms of the molecular conformation in the crystalline regions.
Solution crystallization of nylon 12
Authors: Kyotani Mutsumasa 
Published: April 2003

AbstractElectron microscopy and x‐ray diffraction data have been obtained on nylon 12 crystallized from 1‐hexanol, 1,6‐hexanediol, and hexylene glycol. Ribbonlike lamellar crystals of the γ form are obtained by crystallization from all the solutions and elongated flat crystals of the α form by crystallization from the 1‐hexanol and hexylene glycol solutions. The direction of the hydrogen bond in these crystals is almost parallel to that of maximum crystal elongation. α‐ and γ‐form crystals both grow from 1‐hexanol and hexylene glycol at appropriate crystallization temperatures. γ‐form crystals alone are obtained from 1,6‐hexanediol solution at every crystallization temperature. The long periods measured by small‐angle x‐ray diffraction for the solution‐grown crystals are in the range 7.6–10.6 nm. The melting behavior of the solution‐grown crystals is examined and discussed. The melting temperatures of the γ form may be lower than that of the α form. An equilibrium melting temperature of 208.4°C for γ‐form crystals is obtained by using a relation between thickness of lamellar crystals and their melting temperatures observed by differential scanning calorimeter measurements. Solvents affect the growth of the two crystalline forms in solution crystallization.
Glass transition temperatures of ABA poly(styrene‐b‐isoprene) block copolymers by differential scanning calorimetry
Authors: Meyer G. C. , Widmaier J. M. 
Published: April 2003

AbstractThe glass transition behavior of two sets of ABA poly(styrene‐b‐isoprene) block copolymers was examined by differential scanning calorimetry. In one series, the triblock copolymers had different total molecular weights and the same (30 wt %) polyisoprene content, in the other, the molecular weight was constant (30,000 g/mol) and the elastomer content was the variable. For all triblock copolymers studied, the data show an inward shift for the glass transition temperaturesTgof the corresponding homopolymers. This shift increases for the rigid‐phaseTgas the polystyrene block length decreases. Depending on their molecular characteristics, two, three, or only oneTgwere found. The thirdTgwas interpreted in terms of the existence of an interphase. Some of these conclusions could be confirmed by transmission electron microscopy.
Water mobility in a water‐soaked nafion® membrane: A high‐resolution neutron quasielastic study
Authors: Volino F. , Pineri M. , Dianoux A. J. , De Geyer A. 
Published: April 2003

AbstractWater mobility in an acid Nafion® membrane containing ca. 15% water by weight has been studied by high‐resolution neutron quasielastic scattering (NQES). The data are analyzed in terms of simple models. On a scale of ca. 10 Å, the water molecules move practically as freely as in bulk water, but their long‐range motion is much more hindered. These results are important for an understanding of the relation between the microstructure and the macroscopic properties of these membranes. To our knowledge, this is the first detailed NQES study of the water‐polymer interaction problem.
The kinetics of defect clustering in fibrillar polypropylene crystals
Authors: Petermann J. , Gohil R. M. , Schultz J. M. , Hendricks R. W. , Lin J. S. 
Published: April 2003

AbstractPolypropylene films were produced by solidification during high‐rate (>104s−1) melt drawing. Small‐angle x‐ray scattering (SAXS) data were collected during interruptions of the annealing of these films. Fibrillar crystallization took place during the melt‐drawing process. The fibrils exhibit an axial density modulation as determined by SAXS and transmission electron microscopy. Annealing increases the amplitude of the density modulation. Detailed examination of the SAXS curves shows that the modulation is approximately sinusoidal and that the amplification of the density modulation occurs with no change in periodicity. Comparison of SAXS curves taken at different times during annealing suggests a process similar to spinodal decomposition. It is proposed that the microstructural change within a fibril takes place by the axial motion and clustering of chain defects.
Stress relaxation of a polymer solution in double‐step shear deformations: A separate evaluation of the stress components due to entangled segments of different orientations
Authors: Osaki Kunihiro , Kurata Michio 
Published: April 2003

AbstractWhen two shear deformations γ1 and γ2 are successively applied to an entangled polymeric system, a composite temporary network is formed. In this article a simple method is proposed for evaluating separately the contributions from the component networks of different deformations, γ1 + γ2 and γ2, to the observed shear and normal stresses. The method is applied to literature data for a polystyrene solution. It is revealed that the entangled chain segments formed between the applications of two deformations relax very rapidly, while those formed prior to the first deformation do not relax for quite a long time. The result is in accord with the conjecture based on the tube model of entanglement that the chain ends lose their orientation as the chain creeps out of an oriented tube.
The structure of an aminosilane coupling agent in aqueous solutions and partially cured solids
Authors: Ishida Hatsuo , Naviroj Somsak , Tripathy Sukant K. , Fitzgerald John J. , Koenig Jack L. 
Published: April 2003

AbstractThe molecular structures of partially cured polyaminopropylsilsesquioxane and aminopropyltriethoxysilane in water have been studied using Fourier‐transform infrared, laser Raman, and quasielastic laser light‐scattering spectroscopy. A multiply hydrogen‐bonded structure is proposed for the intramolecularly interacting amine and silanol groups on the basis of isotope exchange experiment and conformational energy calculations. Conformational restrictions are rather low for the proposed structure, which is thus suitable for the partially cured solid where there are slight perturbations by the surrounding amine and silanol groups. The O.…N distance was experimentally determined to be in the range 2.70–2.67 Å and estimated theoretically as 2.49–2.45 Å. The aminosilane in very dilute solution is found to be mostly monomeric. The isolated monomer‐oligomer transition lies around 0.15% by weight and this transition influences the amount of silane uptake by glass fibers. It is also proposed that this phenomenon may be general for surface treatments by silane coupling agents. Hydrolyzed aminosilane oligomers exist in part as submicron aggregates which can be broken up by the addition of an alcohol. The neutralized aminosilane hydrolyzes very slowly although it dissolves in water instantaneously. Micelle formation is also proposed.
Phase transitions in mesophase macromolecules. III. The transitions in poly(ethylene terephthalate‐co‐p‐oxybenzoate)
Authors: Meesiri Wiriya , Menczel Jozsef , Gaur U. , Wunderlich Bernhard 
Published: April 2003

AbstractThe glass and melting transitions of poly(ethylene terephthalate‐co‐p‐oxybenzoate)s have been studied by differential scanning calorimetry. Despite the higher glass transition expected for polyoxybenzoate, there is almost no change in the glass transition temperature up to 63 mol % oxybenzoate (353 ± 4 K). At high oxybenzoate concentration there seems to be a discontinuous jump to a glass transition of 450 K. This high glass transition has been observed in two‐phase materials down to 30 mol % oxybenzoate. The melting transition shows signs of isodimorphism with a minimum in melting temperature at about 60–70 mol % oxybenzoate, 60 K below the melting temperature of poly(ethylene terephthalate). The thermal properties are little affected by the change of the noncrystalline parts of the molecules to a mesophase structure. The transition to the isotropic phase could not be analyzed because of prior decomposition.
The characteristic ratios of stereoirregular polybutadiene and polyisoprene
Authors: Hadjichristidis Nikos , Zhongde Xu , Fetters L. J. , Roovers J. 
Published: April 2003

AbstractThe characteristic ratios of stereoirregular polybutadiene and polyisoprene have been evaluated by a combination of intrinsic viscosity and light‐scattering measurements under θ conditions. The polydienes were synthesized by anionic polymerization and thus had near‐monodisperse molecular weight distributions and were of uniform microstructure. The polybutadiene C∞ was found to be 5.1, which is in good agreement with the Abe–Flory predictions. However, the value of 5.1 for polyisoprene is somewhat higher than prediced by theory.