Crystalline-State Configurations of Alkylene Sulfide Polymers

Abstract

Semi-empirical potential energy functions were used to calculate the conformational energies of several alkylene sulfide polymers of structure [S(CH2)y]. The polymers chosen were those for which crystalline-state configurations were known, specifically those having y=1,2,3, and 5, respectively. The configurations of minimum conformational energy were generally found to correspond to the crystalline-state configurations. The only exceptions occurred for conformational-energy differences close to zero, which is to be expected since in these cases even small differences in intermolecular packing energies could obviously play an important role. Some preliminary comments are also made on the here-to-fore unstudied polysulfides corresponding to y=4, 6, and higher. Comparisons with the corresponding polyoxides [O(CH2)y] help elucidate the effect of the size of the hetero-atom X (S or O), its effective charge, the C–X bond length, and the C–X–C bond angle. The most important difference between the polysulfides and polyoxides appears to be the fact that the C–S bond is considerably longer than the C–O bond.