TACTICITY EFFECTS ON POLYMER BLEND MISCIBILITY .3. NEUTRON-SCATTERING ANALYSIS

The effect of tacticity on the miscibility of a well-known blend system, poly(vinyl methyl ether)/polystyrene (PVME/PS), was investigated through variation of the PVME tacticity. Small-angle neutron scattering (SANS) was used. A two-parameter fit to the SANS data using the random-phase approximation yielded the average statistical segment length for the two blend components and the composition/temperature-dependent scattering interaction parameter, g(sc). Values for g(sc) for a number of compositions and temperatures were fit to the Flory-Huggins-Staverman (F-H-S) equation which accounts for a composition and temperature dependence to g(sc) in terms of the relative surface areas of the blend components. Data were interpreted in terms of an isotactic PVME (i-PVME) statistical segment length which varies with composition and temperature through i-PVME/i-PVME correlations. i-PVME self-correlations were modeled using an analogy with binary chemical reaction kinetics. Structural changes in isotactic PVME due to correlations were directly related to changes in g(sc) as interpreted using the F-H-S structural model for a composition- and temperature-dependent interaction parameter. Correlations between i-PVME interactive units in the blend and far above the equilibrium melting point for isotactic PVME were related to crystallization phenomena in both the free energy of formation for the correlation and the thermal behavior of the correlation as extrapolated using the F-H-S formalism.