MISCIBILITY STUDIES ON BLENDS OF POLYCARBONATE WITH SYNDIOTACTIC POLYMETHYL METHACRYLATE

Miscibility of bisphenol-A polycarbonate (PC) and syndiotactic polymethyl methacrylate (sPMMA) blends was investigated by differential scanning calorimetry (DSC) and small-angle light scattering. Cloud-point measurements indicated the existence of both a lower critical solution temperature and an upper critical solution temperature, forming an immiscibility loop. This immiscibility gap was observed for PC blends with sPMMA of various molecular weights ranging from 8,300 to 55,000. The DSC study on solvent-cast and coprecipitated PC/sPMMA blends from tetrahydrofuran solutions showed a single glass transition, shifting regularly with composition. The annealing of the 50/50 composition within the immiscibility loop exhibited dual glass transitions, but the system reverted to a single phase upon annealing above the loop. Phase dissolution took place during annealing above the loop, followed by thermoxidative branching (cross-linking) reactions. Dry pellets of PC and sPMMA were melt mixed above the loop in a Mini-Max mixer/molder; these molded blends exhibited a single phase. (C) 1993 John Wiley & Sons, Inc.