OBSERVATION OF RESTRICTED MISCIBILITY IN BINARY BLENDS OF POLY(STYRENE-STAT-ACRYLONITRILE) AND POLY(ALPHA-METHYL STYRENE-STAT-ACRYLONITRILE)

Binary blends of two structurally similar copolymers poly(styrene-stat-acrylonitrile) and poly(alpha-methyl styrene-stat-acrylonitrile) were examined by differential scanning calorimetry. A miscibility map constructed for the system showed that the miscibility range was quite restricted and had a significant molecular weight dependence. The system was characterized by using segmental interaction energy densities calculated from earlier work and it was found that a satisfactory description of the miscibility range could only be obtained if a distinction was made between the 'intra' and 'inter' segmental interaction parameters. This sensitivity of the interchange energy to the environment of the segment has been observed in other systems. Consequently it may be an important feature in blends whose miscibility ranges are strongly molecular weight dependent, whereas in less sensitive blends the approximation B(ij)(inter) = B(ij)(intra) is adequate.