Miscibility of poly(vinyl chloride) melts composed of mixtures of chains with differing stereochemical composition and stereochemical sequence

Simulations of coarse-grained models of poly(vinyl chloride) (PVC) on a high coordination lattice have been performed for seven pure melts and 12 binary mixtures composed of chains with seven different stereochemical compositions and stereochemical sequences, at a temperature of 450 K and a density of 1.24-1.26 g/cm(3). The same Lennard-Jones parameters are used for all pairs of monomer units in all of the simulations. The chains differ only in their short-range intramolecular interactions, which are controlled by a rotational isomeric state model for PVC. The melt of syndiotactic PVC is unique in that its intermolecular pair correlation functions (pcf) show a greater tendency for the formation of local "structure" than is evident in the simulations of the other polymers, all of which contain meso diads. The effect of stereochemistry on demixing properties is investigated by simulation of 12 equimolar binary mixtures. The seven binary mixtures that do not contain syndiotactic PVC remain miscible throughout the simulations. However, all but one of the five binary mixtures containing syndiotactic PVC experience demixing during the simulations. The single exception is the binary mixture of syndiotactic PVC with chains in which the sequence of diads has the repeating pattern meso-racemo-racemo-racemo. In this system, the intermolecular pcfs suggest the formation of a weak complex between the chains.