摘要:

AbstractThe problem of the segregation of subchains in an isolated molecule of an A‐B block copolymer is closely related to that of the mutually excluded volume of two chemically differing macromolecules. Therefore, by resorting to the “segment cloud” model used by Flory and Krigbaum to calculate the excluded volume, it was possible to derive an expression for the number of contacts between the two blocks in the same molecule. From the results of the calculation it follows that only partial block segregation can be expected unless the condensation of one of the subcoils to a dense globule occurs, owing to the effect of a poor solvent qu

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100111

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe decay in birefringence of glassy polycarbonate held at constant extension has been studied at 23°C, in the time‐scale range 10–103sec, up to about 6% strain. The results show that, under these conditions, the birefringence can be validly expressed as a linear hereditary integral of the strain history up to a relatively high strain level which is about 3.4% for an experimental time‐scale of 100 sec. Comparison with previously obtained data on the stress relaxation behavior of the same polymer shows that, other factors remaining constant, mechanical relaxation is linear only up to about 1.1% strain. The earlier onset of mechanical nonlinearity is discussed and it is suggested that the mechanical relaxation spectrum is richer than the optical spectrum in relatively long relaxation times, corresponding to relatively slow molecular motions. It is further suggested that these slow molecular motions are accelerated first as the polymer is extended beyond the limit of linear viscoelastic behavior. The observed nonidentity between strain limits for linear mechanical and linear optical behavior is discussed in the light of current practices in photomechanical stress an

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100112

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

摘要:

AbstractThe concentration dependence of the reduced viscosity of a number of polyelectrolytes was found to be adequately described by the equation\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \eta }_{sp} /c = [{\rm \eta }]_\infty [1 + k/\sqrt c ] $\end{document}as long as the concentration is not too low. The parameter [η]∞represents the intrinsic viscosity of the well‐shielded polyion and corresponds to values of [η] determined in salt solutions and may possibly correspond to the theory of Harris and Rice on polyion expansion. Heuristic arguments based in part on the work of Katchalsky et al. lead to a definite expression for the parameterkin terms of molecular properties. This result shows that the above equation is valid only for strong polyelectrolytes with constant activity coefficients of counterion. The calculated values ofkagree well with experiment except when specific intramolecular interactions (e.g., internal hydrogen bonding) occur. For highly charged polyions we find, surprisingly, thatkdepends only on the properties of the polymer backbone and not on electrical prope

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100113

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY

ISSN:0449-2978    

DOI:10.1002/pol.1972.160100114

出版商:John Wiley&Sons, Inc.    

年代:1972

数据来源: WILEY