MISCIBILITY STUDIES ON BLENDS OF POLYCARBONATE WITH SYNDIOTACTIC POLYMETHYL METHACRYLATE

Miscibility of bisphenol-A polycarbonate (PC) and syndiotactic polymet hyl methacrylate (sPMMA) blends was investigated by differential scann ing calorimetry (DSC) and small-angle light scattering. Cloud-point me asurements indicated the existence of both a lower critical solution t emperature and an upper critical solution temperature, forming an immi scibility 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 tetr ahydrofuran solutions showed a single glass transition, shifting regul arly with composition. The annealing of the 50/50 composition within t he immiscibility loop exhibited dual glass transitions, but the system reverted to a single phase upon annealing above the loop. Phase disso lution took place during annealing above the loop, followed by thermox idative branching (cross-linking) reactions. Dry pellets of PC and sPM MA were melt mixed above the loop in a Mini-Max mixer/molder; these mo lded blends exhibited a single phase. (C) 1993 John Wiley & Sons, Inc.