A non-Gaussian theory of rubberlike elasticity based on rotational isomeric state simulations of network chain configurations. III. Networks prepared from the extraordinarily flexible chains of polymeric sulfur and polymeric selenium

Distribution functions for the end-to-end separation of polymeric sulfur [-S-] and selenium [-Se-] are obtained from Monte Carlo simulations which take into account the chains’ geometric characteristics and conformational preferences. Comparisons with the corresponding information on polyethylene [-CH2-] demonstrate the remarkable equilibrium flexibility or compactness of these two molecules. Use of the S and Se distribution functions in the three-chain model for rubberlike elasticity in the affine limit gives elastomeric properties very close to those of simple Gaussian networks, even though their distribution functions appear to be significantly non-Gaussian. Specifically, unlike the case of polyethylene, even very short S and Se chains show only slight upturns in modulus at high elongations; this is consistent with their unusually high flexibility.