TACTICITY EFFECTS ON POLYMER BLEND MISCIBILITY .1. FLORY-HUGGINS-STAVERMAN ANALYSIS

In a previous paper isotactic poly(vinyl methyl ether) (PVME), synthesized in our laboratory, and heterotactic PVME were characterized by GPC, NMR, X-ray diffraction, and DSC. Cloud-point measurements were used to demonstrate that isotactic PVME is less miscible with atactic PS than heterotactic PVME. In this paper Flory-Huggins-Staverman (F-H-S) theory is used to relate shifts in miscibility to changes in the entropic component of the composition-dependent interaction parameter, ''g'', and to changes in the Staverman parameter, ''c''. In the F-H-S approach a composition-dependent interaction parameter is explicitly related to the relative surface areas for lattice sites of the two components. The relative surface area can be determined from low molecular weight materials using the method of Bondi, from simple molecular models, and from a fit to the cloud-point curve. For tactic blends these methods are compared. A distinct difference in the relative surface area for isotactic and atactic PVME is observed which can partially account for shifts in miscibility. A fractionation effect is predicted for polydisperse blends. Uniquely at the critical point fractionation of polydisperse components is not observed.