RELATION OF EFFECTIVE INTERACTION PARAMETERS FOR BINARY BLENDS AND DIBLOCK COPOLYMERS - LATTICE CLUSTER THEORY PREDICTIONS AND COMPARISONS WITH EXPERIMENT

The generalized lattice cluster theory of polymers with structured monomers is used to compute and compare the effective interaction parameter chi(eff) and phase diagrams for diblock copolymer melts and the corresponding binary blends. Predictions are given for general variations of both chi(eff)'s and phase diagrams with thermodynamic state and molecular weights for PS-b-PMMA, PS-b-PVME, and PEP-b-PEE diblock copolymer melts and the corresponding blends. The three microscopic interaction energies for the PS-b-PMMA and PEE-b-PEP systems are obtained from fits to small-angle neutron scattering data, while those for PS-b-PVME melts are taken from our fits to scattering and excess thermodynamic data for the corresponding PS/PVME blend. The junction point in diblock copolymer chains is found to provide an additional large 1/M destabilizing contribution to chi(eff). Calculations performed for an incompressible model cannot explain the small-angle neutron scattering data, and the inclusion of 'equation of state effects'' (or 'compressibility'') is necessary.