摘要:

AbstractThe multiple endothermic behavior of poly(tetramethylene terephthalate) (PTMT) and its random and block copolymers with poly(tetramethylene isophthalate) (PTMI) and poly(tetramethylene oxide) (PTMO) is described. The differential scanning calorimetry heating scans of these polymers exhibit up to four endotherms. Endotherm I, the lowest‐temperature endotherm, is an annealing peak and is ascribed to a clustering of PTMT sequences. Endotherms II, III, and IV are associated with crystal populations originated during periods of isothermal crystallization, cooling, and heating, respectively. The dependence of the endotherms on sample composition, crystallization and annealing temperatures, crystallization and annealing times, and sample cooling and heating rate is discusse

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260501

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThis paper deals with a viscoelastic boundary element method for analyzing a polymer quasifracture usually called a craze in polymers. A time‐dependent boundary stiffness is considered on the quasifracture envelope surface. The viscoelastic property of the glassy polymer is represented by a generalized Kelvin model with multiple retardation times. According to the linear viscoelastic correspondence principle, the associated elasticity solution can be solved by applying the general integral boundary element method. Then the viscoelastic solution in the time domain can be obtained by applying a collocation Laplace inversion transformation. Using these methods, the quasifracture problem composed of an isolated craze opening with time‐dependent stiffness traction in a stressed rectangular plate is analyzed. The displacement profile and the stress distribution around the craze envelope surface are compu

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260502

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractStudied here are miscible binary cosolvents for polystyrene, for which polystyrene is insoluble in either of the individual solvents. Polymer‐solvent interactions in solutions of atactic polystyrene in acetone/diethyl ether and in methylcyclopentane (MCP)/acetone binary cosolvents have been investigated using nuclear magnetic resonance (NMR) spectroscopy. Polystyrene13C chemical shifts were measured as a function of miscible binary solvent compositions and temperature. The NMR data were used to calculate “association constants” as a measure of specific interactions of the solvent components with all sites on the polymer. In mixtures of acetone and diethyl ether,13C‐NMR indicates a weak interaction between the polystyrene phenyl ring and the diethylether solvent component. In the polystyrene/MCP/acetone system, present NMR data reveal no preferential interactions. Additional NMR measurements were performed on polystyrene in mixtures of CCl4/acetone. From these results, it is concluded that although preferential polymer‐solvent interactions are present in some cosolvent systems, they are not a prerequisite for such

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260503

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractEvidence of only a low barrier to inversion in SiOSi sequences could be important with regard to the interpretation of the statistical properties of silicone polymers. The effects are estimated for the temperature coefficients of the unperturbed dimensions, dipole moments, and optical‐configuration parameter for poly(dimethylsilo

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260504

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe ionic interaction of poly(ethylene‐co‐methacrylic acid) ionomer neutralized with Mn2+or Cu2+was studied by ESR spectroscopy to explore the local structure in the ionic aggregate. ESR spectra of the ethylene ionomer were obtained as functions of degree of neutralization and temperature. The existence of both isolated and aggregated cations in the ionomer was confirmed by ESR. In addition, the formation of a Cu2+−Cu2+dimer structure similar to the crystal structure of copper acetate monohydrate was found in ethylene ionomer containing the Cu2+. Cation‐cation interactions changed markedly around 70°C with increasing temperature, representing the onset of the motion of cations in the aggregated ionic s

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260505

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe present paper is concerned with a detailed examination of the formalism and the physical basis of the dual mode mobility model used for the theoretical description of gaseous transport in glassy polymers in the light of recent theoretical and experimental work. It is shown that there are no really major differences among the original formulation of the model and later variants. A major modification becomes necessary, however, if the Langmuir sorption mode is assumed to exist in the form of patches or domains extensive enough to constitute a macroscopically recognizable phase rather than in the commonly accepted from of scattered individual adsorption sites. It is shown that the proper treatment of this case reduces to the familiar dual mode mobility formalism only under certain conditions. The interpretation of the experimental results thus far available is considered in some detail, and the usefulness of each of the aforesaid approaches in this respect is discussed.

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260506

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effect of stereoregularity on gas permeation properties of poly(methyl methacrylate) (PMMA) was investigated. The gas permeability coefficients for He, H2, O2, N2, Ar, CH4, and CO2at 35°C near atmospheric pressure have been measured for three different PMMAs. Apparent diffusion and solubility coefficients were obtained from time lag data, and these were compared with data for a commercial PMMA previously reported. The permeability, solubility, and diffusion coefficients increase as the content of syndiotactic sequences increases. These observations are consistent with more dense packing of the isotactic form in the glassy state that stems in part from its lower glass transition temperature. The transport behavior for a 50:50 isotactic/syndiotactic blend was also studied. These so‐called stereocomplexes exhibit permeation behavior comparable to other weakly interacting miscible blend syste

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260507

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractSorption isotherms for carbon dioxide in a homogeneous dense cellulose acetate membrane were measured by the pressure decay method at three temperatures between 20 and 40°C and gas pressures up to 1.7 MPa. Steady‐state permeation rates for the same system at three temperatures between 24 and 40°C and gas pressures up to 2.2 MPa were measured by the variable volume method. The equilibrium sorption was described well in terms of the dual‐mode sorption model. The pressure dependence of the mean permeability coefficient was interpreted by the total immobilization model, i.e., a limiting case of the dual‐mode mobility model, where the diffusion coefficient for the Henry's law mode is not assumed to be constant but depends upon gas pressure via a modified free‐volume theory. The observed pressure dependence of the mean permeability coefficient through an asymmetric cellulose acetate membrane was very similar to that through a homogeneous dense membrane. The thin skin layer in the asymmetric membrane can be simulated by a homogeneous dense membrane from the point of view of gas sorption and

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260508

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractA classification is given of flexible, semicrystalline polymers based on the early stage deformation behavior in the solid state. The criteria of each category are discussed with experimental evidence from the literature on 17 polymers. The central aim of this classification is to point out the possibility of ductility induced during deformation. The understanding of the induced ductility in a given semicrystalline polymer suggests a systematic route to optimize solid‐state deformation processes for achieving high draw ratio

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260509

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe free‐volume theory of diffusion is used to analyze the temperature dependence of solvent self‐diffusion coefficients both above and below the glass transition temperature at concentrations removed from the pure polymer limit. The glass transition can have a pronounced effect on the temperature dependence of solvent self‐diffusion coefficients at small solvent concentrations, but the theory predicts a decreased effect of the transition on the diffusion process with increasing solvent concentr

ISSN:0887-6266    

DOI:10.1002/polb.1988.090260510

出版商:John Wiley&Sons, Inc.    

年代:1988

数据来源: WILEY