Changes in the glass transition temperature of end-linked networks as a result of the cure process have been studied by examination of a series of stoichiometrically imbalanced PDMS networks covering a wide range of stoichiometric ratio values. The data were compared to existing theories in an effort to resolve the question of cross-link contribution to Tt. The results support the notion based on the Gibbs-DiMarzio theory that elastically effective junctions rather than any branch point dominate the contribution of cross-links to Tt. It has also been shown that existing theories are capable of predicting cure-related changes in Tt for a variety of cross-linked systems.

Model polyelectrolyte networks having controllable and independently known structural characteristics were prepared from different molecular weights of a, -amino-terminated poly(acrylic acid), by cross-linking them with a trifunctional isocyanate coupling agent. The density of cross-links, average molecular weight between cross-links, and the functionality of the cross-link points of these networks have been characterized. The swelling behavior of these novel networks was studied as a function of bath pH and ionic strength and the results were interpreted in term of structure-property relationships of the polymeric compounds. The maximum hydration was achieved at values of pH greater than 7. Hydration was linearly dependent upon the average molecular weight between cross-links, Mc. The hydration relative to this maximum value, flrei = H/fímax, was a function of pH but not of Mc. The relative hydration, HK\, and fraction of carboxyl groups ionized, a, were similar functions of the pH of the equilibrating solution. In previous studies, on randomly cross-linked polyelectrolyte networks, Mc could not be directly characterized by experimental measurements and has been inferred using theoretical models. In this study, we have directly related the network structural parameters, which were imposed by the synthetic route used and confirmed experimentally, to the macroscopic swelling behavior observed without invoking any theoretical models.

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