THERMAL-ANALYSIS AND OPTICAL MICROSCOPY OF MODIFIED POLYSTYRENE POLY(ETHYL ACRYLATE) BLENDS CONTAINING SPECIFIC INTERACTIONS

The effect of specific interactions on the mixing behavior of sulfonated polystyrene (SPS) and ethyl acrylate/4-vinylpyridine copolymers (EAVP) has been examined using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and optical microscopy. For both the acid and zinc-neutralized forms of SPS, blends at a 2% substitution level show two phases consisting of the pure components, although DSC data indicate that some enhanced mixing compared to the unfunctionalized blend has occurred at the interface. Blends of higher substitution levels show predominantly a mixed phase by DMTA. Optical microscopy shows that 2% interacting groups is enough to result in a dramatic change in the blend morphology; the domains become much smaller and more uniform in size compared to the unfunctionalized blend. The results are interpreted in terms of a model in which the interactions are considered to be cross-links, and thus phase separation occurs for all blends to the extent allowed by the topological constraints imposed by the interacting groups.