Examination of the Critical Parameters in the Constrained Junction Theory of Rubber Elasticity

Abstract

Stress-strain data previously obtained for a wide variety of unswollen and swollen polymer networks in elongation are interpreted by using the Flory-Erman theory of rubber elasticity. The interpretation is carried out as objectively as possible, with theoretical curves chosen on the basis of minimum residuals between theory and experiment and with realistic estimates of the uncertainties involved. High-elongation values of the reduced stress obtained from the theoretical curves were found to be very nearly independent of the degree of swelling. They differed significantly, in some cases, from the intercepts (2C1) obtained by simple linear extrapolations of the data. Low-elongation values, however, are quite close to the linearly extrapolated values. In the theory employed, the reduced stress depends on the extent to which junction fluctuations are constrained, which in turn depends on the degree of interpenetration of the chain configurational domains. Values of an interpenetration parameter, although defined to account for the configurational characteristics of the chains investigated, were unfortunately found to show some dependence on the degree of swelling and the nature of the elastomeric chains. © 1986, American Chemical Society. All rights reserved.