摘要:

AbstractTwo very different high‐modulus polyethylene fiber samples, a low molecular weight melt‐spun and drawn fiber, and a high molecular weight gel‐spun and drawn fiber, have been subjected to electron beam irradiation to various doses in vacuum and in the presence of acetylene. The gel content after irradiation in acetylene was found to be much greater than for an equivalent dose in vacuum. The gel content–dose relationship could not be described by either Charlesby–Pinner analysis or the Inokuti equation. This is attributed to the polydispersity and the complications introduced by the unique morphologies of highly drawn fibers. Following previous studies, the tensile creep behavior was interpreted in terms of a model comprising two thermally activated processes in parallel, a low stress process relating to the amorphous network, and a high stress process relating to the continuous crystal fraction. Analysis of the creep behavior of the melt‐spun, low molecular weight fiber irradiated in vacuum revealed crosslinking in the amorphous regions and chain scission in the crystal. Chain scission was found to be much reduced when irradiating in acetylene, for which a mechanism has been proposed. The creep rates and activation volumes of the high molecular weight, gel‐spun fiber were found to be significantly lower, probably due to the unique morphology. In this case the dominant effect of irradiation on the mechanical properties can be attributed to chain scission rather than

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250701

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractA molecular theory for small‐angle neutron scattering from polymer mixtures is reviewed and extended to consider multiphase polymer systems such as block copolymers and their blends with homopolymers. Methods are developed for the isolation of scattering functions for individual components in these blends. These methods rely on two contrast‐matching techniques: the concept of “composition matching,” where a mixture of deuterium‐labeled and protonated species is used to match the contrast of a third component; and the synthesis of “phase‐matched” block copolymers, where the contrast of the block copolymer sequences are matched. Methods are discussed specifically for the isolation of single chain and single sequence scattering functions for diblock and triblock copolymers, their blends with homopolymers, and

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250702

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractApparent molal heat capacities as a function of the degree of neutralization have been determined for dilute aqueous solutions of poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), copoly(maleic acid‐ethylene) (MAEt), and copoly(maleic acid‐styrene) (MASt) using direct flow microcalorimetry. Apparent molal volumes were measured as well. Both molal heat capacity and molal volume decrease with increasing ionization of the polymer. The effect of the hydrophobic interactions of the methyl group or phenyl group was obtained from the difference in the molal quantities of PMA and PAA, or MASt and MAEt. No evidence of hydrophobic effects, as determined from the heat capacity, was found for the conformational transition of PMA, but the hydration of the phenyl groups in MASt was found to be changed significantly at a degree of neutralization of

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250703

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe effect of counterions on the solution properties of two types of ionomers, one based on sulfonated polystyrene and the other based on styrene–methacrylic acid copolymer, was studied by viscosity and light scattering measurements. It was found that the order of counterion binding of ionomers in a polar solvent and the order of aggregation of ionomers in a low‐polarity solvent were the same for the same ionomer system. However, the order for the sulfonated ionomer was Li

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250704

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractCarbon‐13 and proton spin‐lattice relaxation times were measured at two field strengths on solutions 10% by weight of two polycarbonates in C2D2Cl4from −20 to +120°C. The first polycarbonate is an asymmetrically substituted form with one chlorine on one of the two phenylene aromatic rings of the bisphenol unit, whereas the second polycarbonate is symmetrically substituted with two chlorines on each of the two rings. The nuclear spin relaxation data are interpreted in terms of several local motions likely in these polymers. Segmental motion was described by the Hall–Helfand correlation function. Segmental motion in the monosubstituted polycarbonate is somewhat slower than in unsubstituted polycarbonate, whereas segmental motion in the tetrasubstituted polycarbonate is considerably slower. Phenylene ring rotation is observed in unsubstituted polycarbonate and in the monosubstituted polycarbonate above 40°C. Below 40°C in the monosubstituted species, and at all temperatures in the tetrasubstituted species, ring rotation is replaced by ring libration as the predominant motion contributing to spin lattice relaxation. In addition, the rotational motion of the two types of rings in the asymmetric monosubstituted form are very similar although not identical. The substituted ring is slightly less mobile than the rings of unsubstituted polycarbonate. This indicates a strong coupling of ring motion, although the coupling leads to less than synchronous motion. Methyl group rotation is present in both polymers and is little affected by the various structural mod

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250705

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe tetracyanoethylene anion radical (\documentclass{article}\pagestyle{empty}\begin{document}${\rm TCNE}^{ \cdot ^ - } $\end{document}) was detected by ESR spectroscopy in polytetrafluoroethylene (PTFE), which had been mechanically fractured in vacuo with tetracyanoethylene (TCNE) at 77 K. The assignment of\documentclass{article}\pagestyle{empty}\begin{document}${\rm TCNE}^{ \cdot ^ - } $\end{document}was carried out by ESR spectral simulation on the basis of an anisotropic effective hyperfine tensor that included a forbidden transition term. The\documentclass{article}\pagestyle{empty}\begin{document}${\rm TCNE}^{ \cdot ^ - } $\end{document}is formed by abstraction of an electron by TCNE from the anion that is produced by heterogeneous scission of the carbon‐carbon bond in the main chain of PTFE. At least 16% of the scission of the main chains of PTFE occurs by a heterogeneous process to produce the anions. Approximately 50% of the anions decay during annealing for 30 min at 220 K in the dark, and all anions decay within 15 min at 325

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250706

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractWe have used the pulsed‐gradient spin‐echo NMR method to measure diffusion in a highly polydisperse polymer, a hydroxyl‐terminated polybutadiene. We have modelled the expected spin‐echo attenuation assuming that the low‐molecular‐weight fractions are unentangled and constitute a Rouse‐like diluent to the entangled larger molecules. Fitting this simulation to our data is consistent with the model and permits the extraction of the range of diffusivities and a semiquantitative value for the molecular weight above which entanglements inhibit diffusion. The model is extended to include a monodisperse diluent present additionally, e.g., a curing agent. This extension is tentatively applied to polybutadiene resins undergoing curing and shows that the diffusivity of the remaining unreacted curing agent is little affected by network formation, whereas the retardation of the unreacted polymer molecules is cl

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250707

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe miscibility of bisphenol‐A polycarbonate (PC) with poly(methyl methacrylate) (PMMA) has been reexamined using differential scanning calorimetry (DSC) and optical indications for phase separation on heating, i.e., lower critical solution temperature (LCST) behavior. Various methods have been used to prepare the blends including methylene chloride (CH2Cl2) and tetrahydrofuran (THF) solution casting, melt mixing, and precipitation of PC and PMMA simultaneously from THF solution by using the nonsolvents methanol and heptane. It is shown that the resulting phase behavior for PC/PMMA blends is strongly affected by the blend preparation method. However, these blends are miscible over the whole blend composition range (unambiguous single composition‐dependentTg's and LCST behavior) when prepared by precipitation from solution using heptane as the nonsolvent. To the contrary, solution‐cast and melt‐mixed PC/PMMA blends were all phase separated, which may be attributed to the “solvent” effect and LCST behavior, respectively, not discovered in previous reports. Methanol precipitation does not lead to fully mixed blends, which demonstrates the importance of the choice of nonsolvent when using the precipita

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250708

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe translational diffusion coefficients for three relatively short, nearly monodisperse polystyrene chains (with molecular weights 2000, 4000, and 9000) in liquid cyclohexane have been measured up to 523.2 K using the extended Taylor dispersion method. The resultant hydrodynamic radii are successfully interpreted with the freely jointed chain model corrected for the approximations intrinsic to Kirkwood's theory with Stokes' radius as the only adjustable parameter, which is found to decrease with chain length but approach a constant value for long enough chains. The experimentally observed hydrodynamic radii of polystyrene standards with molecular weights 17,500, 50,000 and 100,000 at 308.2 K conform quite well to the values predicted with the approach formulated in this work.

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250709

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractStudies on solute–solvent interactions of oligo(m‐benzamide)s inN,N‐dimethylacetamide (DMA) have been carried out. The enthalpies of solution have been measured for oligo(m‐benzamide)s and oligo(m‐phenylene)s in DMA and benzene. Contributions of enthalpies of cavitation and dispersion interaction to the enthalpy of transfer from benzene to DMA, ΔHtr(Ben → DMA), have been examined for oligo(m‐phenylene)s. A considerable contribution of excess enthalpy, ΔHE(Ben → DMA), to ΔHtr(Ben → DMA) has been found, which increases with the number of benzene rings of the solute. By assuming that ΔHE(Ben → DMA) of diphenyl (DP) is equal to that of benzanilide (BA) in DMA, the amide hydrogen bond enthalpy of BA in DMA, ΔH HBBAestimated by “the pure base method” corrected for the enthalpies of cavitation and dispersion interaction. The ΔH HBBAvalue has been given by the following expression including the unknown solubility parameter of BA, δBA:\documentclass{article}\pagestyle{empty}\begin{document}$$ {{\Delta H_{{\rm HB}}^{{\rm BA}} } \mathord{\left/ {\vphantom {{\Delta H_{{\rm HB}}^{{\rm BA}} } {{\rm kJ mol}^{ - 1} {\rm } = {\rm } - 30.1{\rm } + {\rm }0.990\left( {\frac{{\delta ^{{\rm BA}} }}{{{\rm J}^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm cm}^{{{ - 3} \mathord{\left/ {\vphantom {{ - 3} 2}} \right. \kern-\nulldelimiterspace} 2}} }}} \right)}}} \right. \kern-\nulldelimiterspace} {{\rm kJ mol}^{ - 1} {\rm } = {\rm } - 30.1{\rm } + {\rm }0.990\left( {\frac{{\delta ^{{\rm BA}} }}{{{\rm J}^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm cm}^{{{ - 3} \mathord{\left/ {\vphantom {{ - 3} 2}} \right. \kern-\nulldelimiterspace} 2}} }}} \right)}} $$\end{document}The evaluation of δBAhas resulted in the conclusion that −ΔH HBBAis smaller than 10.9 kJ mol−1. Moreover, ΔHtr(TMU → DMA) for oligo(m‐benzamide)s has been examined. It has been shown that the amide hydrogen bonding ability of DMA is lower than that of TMU. The linearity of the plot of ΔHtr(TMU → DMA) against the number of amide bonds in the molecule has been explained by the increase in hydrogen bond enthalp

ISSN:0887-6266    

DOI:10.1002/polb.1987.090250710

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY