Effect of Partial Miscibility on the Modulus of Polycarbonate/Poly(styrene-co-acrylonitrile) Blends

The composition of conjugate phases in blends of polycarbonate, PC, and poly(styrene-co-acrylonitrile), PSAN, was calculated with the aid of observed glass transition temperatures. Solubility of PSAN (or PC) in the PC-rich (or PSAN-rich) phase increases with decreasing volume fraction of PC (or PSAN) in blends. With regard to literature data, this trend is qualitatively explained as a consequence of the polydispersity of components because only the fractions with lower molar mass can be exchanged between the conjugate phases. As the modulus of conjugate phases in heterogeneous blends cannot be measured, it is approximately estimated as that of the blends containing 10-15 vol% of totally miscible minority component. Positive deviation of the moduli of partially miscible blends, which are compared with theoretical values calculated by using the equivalent box model combined with percolation approach, is ascribed to the fact that moduli of conjugated phases are higher than those of parent polymers. The increased modulus of conjugate phases is interpreted as a result of suppressed molecular mobility due to associative interactions between the chains of components in both present phases. © ChemTec Publishing.