TACTICITY EFFECTS ON POLYMER BLEND MISCIBILITY .2. RATE OF PHASE-SEPARATION

Cloud-point curves of isotactic and atactic poly(vinyl methyl ether) (i- and a-PVME) blended with atactic polystyrene (PS) were analyzed using the Flory-Huggins-Staverman (F-H-S) approach in the first paper1 of this series. A functional form for the composition-dependent interaction parameter, ''g'', in these two polymer blends was obtained. In this paper the ''g'' functions previously obtained are used to predict the rate of phase separation in terms of the apparent diffusion constant. The F-H-S analysis of cloud-point curves predicts a drastically slower rate of phase separation for i-PVME in blends with PS in comparison with a-PVME blends. The rate of phase separation is experimentally determined for these two polymer blends using light scattering. A comparison is made between the measured apparent diffusion constant and that predicted from simple cloud-point measurements using the F-H-S approach. The experimental kinetics data agree with the drastically slowed rate of phase separation predicted for the isotactic blend. A comparison of F-H-S results and the measured kinetics yields a translational diffusion constant which agrees with literature values. A brief discussion of a novel analysis of light scattering data from intermediate-stage phase separation is also presented. This analysis is based on a modified Cahn-Hilliard approach and uses the ''g'' functions obtained from cloud-point curves using the F-H-S approach.