IN-SITU POLYMERIZATION OF BISPHENOL-A-CARBONATE CYCLIC OLIGOMERS IN MISCIBLE BLENDS WITH A STYRENE-ACRYLONITRILE COPOLYMER - PHASE-SEPARATION DYNAMICS AND THE INFLUENCE OF PHASE DISPERSION ON DUCTILITY

The in situ polymerization of bisphenol-A-carbonate cyclic oligomers ( BPACY)/styrene-acrylonitrile copolymer (SAN) blends has been demonstra ted to yield PC/SAN blends with morphologies unattainable via conventi onal melt blending. Extremely fine phase dispersion can be obtained by this method of blend preparation. Domain-coarsening kinetics have bee n shown to be quite sensitive to the volume fraction of the dispersed phase. The 'pinning' of domain coarsening, unique to polymer systems, can be attributed to the extreme barriers to diffusive coarsening mech anisms in these systems. Thus, phase coarsening is arrested when perco lation ceases or domains no longer form local clusters. The dispersed phase size has been shown to have a dramatic effect on high-stress def ormation in systems where a brittle phase is dispersed in a more compl iant ductile matrix. The increased ductility of blends with finer phas e dispersions has been rationalized based on a lower tendency for smal ler brittle phases to craze and crack in addition to the influence of complex local stress fields in heterogeneous materials.