SEGMENTAL DYNAMICS AND INCOMPATIBILITY IN HARD SOFT POLYMER BLENDS/

We report on the segmental dynamics of the binary polymer blend polyst yrene (PS)/poly(methylphenylsiloxane) (PMPS) in the two-phase region u sing dielectric spectroscopy that essentially probes the PMPS componen t. Based on the experimental orientation relaxation functions, the ave rage glass transition temperature T-g controls phase separation. When the spinodal temperature T-s exceeds T-g, the PMPS segmental relaxatio n displays two distinct decays characteristic of a merely pure and a m ixed, roughly at the initial composition, PMPS regions. On the contrar y, when T-s falls in the proximity of T-g, the PMPS relaxation is stro ngly nonexponential and its average time reflects mixed regions rich i n PMPS due to incomplete phase separation, which drives only the glass y phase out of local thermodynamic equilibrium. Distinct morphological differences in the two-phase state of these blends, inferred from the ir segmental dynamics, are revealed by transmission electron microscop y. (C) 1998 American Institute of Physics.