TOWARDS A MOLECULAR-BASIS FOR UNDERSTANDING THE BEHAVIOR OF ISOTOPIC POLYMER BLENDS - LATTICE CLUSTER THEORY COMPUTATIONS FOR PSD PSH BLENDS

The binary blend lattice cluster theory (LCT) is applied to isotopic p olystyrene (PSD/PSH) blends to study the combined influence on blend p hysical properties of local correlations, monomer molecular structure, and blend compressibility, as well as of asymmetries in interactions, molecular weights, and monomer structures. The LCT computations of th e small-angle neutron scattering effective interaction parameter chi(e ff), the coexistence curve, and the interfacial profile in phase-separ ated PSD/PSH blends provide good agreement with experimental data, ind icating internal consistency. The computations do not yield the parabo lic upward composition dependence of chi(eff) that is observed for iso topic blends of polybutadienes and polyethylenes. We speculate that th is upward behavior arises from the random copolymer nature of these sy stems.