PROPERTY AND MORPHOLOGY RELATIONSHIPS FOR TERNARY BLENDS OF POLYCARBONATE, BRITTLE POLYMERS AND AN IMPACT MODIFIER

Mechanical properties and the morphology of ternary blends of polycarbonate (PC) with a methacrylated butadiene-styrene (MBS) impact modifier and various brittle polymers (BP), like polystyrene (PS), styrene/acrylontrile (SAN) copolymers, and poly(methyl methacrylate) (PMMA), have been investigated. Component pair miscibility, interfacial energies and mixing sequence influence phase morphology and blend properties. Blends prepared by a two-step mixing sequence usually exhibited better properties than those prepared by mixing all components simultaneously. A surface energy analysis is developed for predicting the locus of the MBS particles in the two-phase matrix. This scheme combined with knowledge of pair miscibility proved to be a useful predictive method. It was predicted and found that MBS particles often become trapped at the PC-BP interface by surface forces. Significant toughening of PC blends with PMMA and SAN, but not with PS, was obtained by addition of the MBS impact modifier. For some of the ternary blends, high levels of toughness and reduced notched sensitivity were achieved without any loss of modulus relative to polycarbonate.