Model networks of end-linked polydimethylsiloxane chains. IX. Gaussian, non-Gaussian, and ultimate properties of the trifunctional networks

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Abstract
Model elastomeric networks were prepared by end‐linking hydroxyl‐terminated polydimethylsiloxane chains with a trialkoxy silane. Mixtures of various proportions of relatively long and very short chains were employed, since the resulting ’’bimodal’’ networks are of unique importance in characterizing non‐Gaussian effects related to limited chain extensibility. Stress–strain isotherms of these trifunctional networks gave values of the elongation at which the modulus begins to increase anomalously, and values of the elongation and modulus at the point of rupture. These results were interpreted in terms of calculated values of the maximum extensibilities of the chains, and were compared with previously reported results on the corresponding tetrafunctional networks in order to characterize the effects of crosslink functionality on these properties. In addition, the elasticity constants characterizing the Gaussian regions of the isotherms, and values of the degree of equilibrium swelling were used to evaluate the most recent molecular theories of rubberlike elasticity, particularly with regard to how the elastic effectiveness of the network chains depends on chain length and extent of deformation.