摘要:

AbstractA single master logarithmic stress relaxation curve of reduced modulus as a function of reduced time is established for a styrene‐butadiene rubber (SBR) system, accounting for the effects of crosslinking density, temperature, and time. The results from recent tests involving uniaxial and various biaxial strain states at finite strain levels may be represented by a unique strain‐energy functionWof the Valanis‐Landel separable symmetric type,\documentclass{article}\pagestyle{empty}\begin{document}$ W = \sum\limits_{i = 1}^3 {w(\lambda_i)} $\end{document}where the λiare principal extension ratios. These two representations demonstrate that the mechanical response of whole families of elastomeric materials may be predicted once a single member of the family is fully charact

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200301

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThis article proposes a temperature‐jump (T‐jump) approach for characterizing the kinetics of volume recovery in glassy materials. The kinetic characterization is based on the Kovacs‐Aklonis model. This incorporates a retardation‐time spectrum which shifts according to both the temperature and the instantaneous volume. The proposed experiments involve measuring the change in recovery rate caused by an abrupt temperature jump. Although an analogous procedure has been used to determine the activation energy for linear viscoelastic creep, the analysis for volume recovery is complicated by its inherent nonlinearity. Nevertheless, accounting for the nonlinearity by a reduction of the time scale permits the T‐jump results to be analyzed. In particular, the T‐jump approach can be used to: (i) test a particular functional form for the shift factor and (ii) determine the previously unmeasurable parameterx, which defines the relative importance of the temperature dependence and the volume dependence in this function. In addition, numerical simulations indicate that the proposed method can be implemented in the

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200302

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

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 micro

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200303

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractPolymer‐substrate interaction energetics have been determined in order to describe the epitaxial deposition of polyethylene into graphite. The potential energy was calculated using van der Waal's interactions. A closed‐form representation of the potential was derived for a substrate which was considered infinite in planar area. Inspection of the relative polymer‐substrate energies for various positions above the substrate indicate a planar‐zigzag polyethylene chain segment deposits with its backbone parallel to the substrate. The chain axis preferentially orients in the (1120) directions of the graphite surface layer. Specifically, deposition occurs along the lines which intersect the nearest‐neighbor midpoints of the CC bonds in the su

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200304

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe use of pulsed laser excitation upon a series of 1‐vinylnaphthalene/methyl methacrylate co‐polymers in which the intramolecular chromophore concentration is varied over a wide composition range has allowed the individual rate constants governing intramolecular excimer formation to be determined at various temperatures between 205 and 295 K. Triple exponential functions are necessary for adequate description of the photophysical kinetics over the entire temperature range. It is proposed that the kinetic and temperature behavior is consistent with a kinetic scheme involving two kinetically distinct monomeric species and an excimer in which energy may be transferred from the second monomer M*2to the first monomer M*1which can interact with the excimer by a conventional migration mechan

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200305

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractOn the basis of the Leonov viscoelastic constitutive equation, oscillatory shear flow of elastic fluids in the linear and nonlinear regimes has been considered. The Fourier components and associated phase angles of the shear and normal components of the elastic strain tensor have been found as functions of frequency and deformation amplitude in the range usually employed in experiment, and are presented in a form convenient for further rheological applications. In the linear case, the results correspond to many known theories. In the nonlinear case, the theoretical results have been compared with experiments, on different polymeric systems, with very good agreement being obtained for the shear stress in polymeric solutions but only qualitative agreement for the shear stress and first normal‐stress difference in polymer melt

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200306

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractA description is given of an analytical temperature‐rising elution fractionation (TREF) system for the purpose of determining short‐chain branching (SCB) or copolymer distributions in poly‐ethylenes and ethylene copolymers. The system achieves fractionation on the basis of crystallizability and is shown to be very little influenced by molecular weight in the normal high polymer range. Sample preparation by slow cooling from relatively dilute solution followed by continuous elution with a simultaneous and fairly rapid rate of temperature rise proves to be an efficient fractionation process. An on‐line detector and data system allows application of a calibration curve to give realistic SCB distribution data in a convenient manner. The potential value of the TREF technique for providing structural information is illustrated by examples which include low‐density high‐pressure resins made by both tubular and autoclave reactors, high‐ and low‐density resins made by low‐pressure processes, and copolymers of ethylene with vinyl acetate a

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200307

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThin films of a polyester of lactic and glycolic acid were prepared to give controlled amounts of disk spherulites. The spherulite contents ranged from zero to 100% and were accurately measured. The stress‐strain properties of the films were then determined at 60°C, i.e., about 20°C above the glass transition temperatureTg. The mechanical behavior varied quite systematically with spherulite content and displayed little dependence on spherulite size. It was found that much of the mechanical data could be reasonably well described by a simple composite model. In addition, the yield strain as well as the strain to break could be principally coupled to the deformation of only the amorphous phase. SEM and optical microscopy studies supported the above conclusion, also demonstrating that the isolated spherulites adhered well to the amorphous matrix and behaved as stress concentrators in the system when the deformation temperature was abov

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200308

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractBimodal networks consisting of very short and relatively long poiydimethylsiloxane (PDMS) chains were studied from 30 to −52°C in an attempt to elucidate the anomalous increases in modulus [f*] exhibited by such elastomeric materials at high elongations. Temperature was found to have very little effect on (i) the elongation at which the upturn in [f*] becomes discernible, (ii) the elongation at which rupture occurs, and (iii) the total increase in [f*] up to the rupture point. The standard force‐temperature (“thermoelastic”) plots were linear, but gave values of the energetic contribution to the total force which were significantly smaller than those universally obtained on unimodal, long‐chain PDMS networks. Birefringence‐temperature relations were also found to be linear, and yielded values of the optical‐configuration parameter and its temperature coefficient which were in satisfactory agreement with the corresponding values reported for unimodal PDMS networks. These results indicate that even at very low temperatures the observed increases in modulus (and consequent improvements in ultimate strength) are due to non‐Gaussian effects arising from limited chain extensibility, rather than from intermolecular reinforcing effects such as strain‐induc

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200309

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

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

ISSN:0098-1273    

DOI:10.1002/pol.1982.180200310

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY