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 hig h coordination lattice have been performed for seven pure melts and 12 bina ry mixtures composed of chains with seven different stereochemical composit ions 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 pa irs of monomer units in all of the simulations. The chains differ only in t heir short-range intramolecular interactions, which are controlled by a rot ational isomeric state model for PVC. The melt of syndiotactic PVC is uniqu e in that its intermolecular pair correlation functions (pcf) show a greate r tendency for the formation of local "structure" than is evident in the si mulations of the other polymers, all of which contain meso diads. The effec t of stereochemistry on demixing properties is investigated by simulation o f 12 equimolar binary mixtures. The seven binary mixtures that do not conta in syndiotactic PVC remain miscible throughout the simulations. However, al l but one of the five binary mixtures containing syndiotactic PVC experienc e demixing during the simulations. The single exception is the binary mixtu re of syndiotactic PVC with chains in which the sequence of diads has the r epeating pattern meso-racemo-racemo-racemo. In this system, the intermolecu lar pcfs suggest the formation of a weak complex between the chains.