Study of the compatibility of blends of polymers and copolymers containing styrene, 4-hydroxystyrene and 4-vinylpyridine

Differential scanning calorimetry was used to show that poly(4-vinylpyridine) is incompatible with polystyrene but compatible with poly(4-hydroxystyrene) over the entire range of composition. Compatibility between poly(4-vinylpyridine) and styrene-rich copolymers is achieved by introducing into the copolymers reactive groups which are able to complex with poly(4-vinylpyridine) through hydrogen bonding. For example, it was found that poly(4-vinylpyridine) is compatible with a copoly(styrene-4-hydroxystyrene) containing 50 mol% of 4-hydroxystyrene units over the entire range of blend composition; however, if the styrene copolymer contains only 20-30 mol% of 4-hydroxystyrene units, compatibility is only achieved for blends which are rich in poly(4-vinylpyridine). Similarly, miscibility between poly(4-hydroxystyrene) and polystyrene, which are incompatible over the entire range of composition, is only achieved if polystyrene is modified by incorporation of large amounts of (4-vinylpyridine) units. Hence, compatibility is achieved for poly(4-hydroxystyrene) and a copoly(styrene-4-vinylpyridine) containing 50 mol% of 4-vinylpyridine units. But a similar copolymer containing only 20 mol% of 4-vinylpyridine does not form a compatible blend with poly(4-hydroxystyrene). These results confirm that for such dissimilar polymers compatibility can only be achieved through cumulative interactions of added functionalities.