LIGHT-SCATTERING ANALYSIS OF UPPER CRITICAL SOLUTION TEMPERATURE BEHAVIOR IN A POLY(VINYLIDENE FLUORIDE) POLY(METHYL METHACRYLATE) BLEND

We carried out the light scattering studies under both H(V) and V(V) optical alignments on the competitive progress of the crystallization and the liquid-liquid phase separation in a blend of poly(vinylidene fluoride) and poly(methyl methacrylate) after the temperature drop from a single-phase melt to various low temperatures. The upper critical solution temperature (UCST) type phase boundary below the melting temperature was determined by the temperature dependence of three kinetic variables of the liquid-liquid phase separation: (1) the initial slope of the time variation of the invariant of V(V) scattering, (2) the most probable wavenumber of concentration fluctuation having the highest rate of growth, and (3) the apparent diffusion constant. The critical temperatures estimated by the three different methods agreed well with each other and showed a similar composition dependence. The critical temperature was also determined by a kinetic discussion on the crystallization affected by the liquid-liquid phase separation, and it was found to be nearly equal to those estimated by the three methods. The results strongly justify the UCST type phase behavior. Combining the literature data, the phase diagram of the binary system was drawn in terms of the UCST, the melting point depression, and the LCST (lower critical solution temperature) curves.