Model networks of end‐linked polydimethylsiloxane chains. XII. Dependence of ultimate properties on dangling‐chain irregularities

Abstract

AbstractElastomeric networks were prepared by end‐linking vinyl‐terminated polydimethylsiloxane (PDMS) chains having number‐average molecular weights of 11.3 × 103 g mol−1. The tetra‐functional end‐linking agent, Si[OSi(CH3)2H]4, was used in varying amounts smaller than that corresponding to a stoichiometric balance between its active hydrogen atoms and the chain vinyl groups. The number of dangling‐chain irregularities thus introduced into the networks was directly determined by iodometric titration for unreacted vinyl groups. The (unfilled) PDMS networks thus obtained were studied in elongation to their rupture points at 25°C (a temperature sufficiently high to prevent complications from strain‐induced crystallization), and in swelling equilibrium in benzene at room temperature. Small to moderately large proportions of dangling chains were found to have less of an effect on the elongation modulus than might be expected, and similarly a relatively small effect on the degree of equilibrium swelling. Most importantly, comparisons of constant values of the high deformation modulus show that dangling‐chain irregularities decrease both the maximum extensibility of a network and its ultimate strength.