Miscibility of styrene and t-butyl acrylate random copolymers and their ionomers with poly(2,6-dimethyl-1,4-phenylene oxide)

A series of poly(styrene-ran-t-butyl acrylate) (S-tBA) copolymers was prepared and characterized. The S-tBA copolymers containing less than ca. 23 mol% t-butyl acrylate were found to be miscible with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) at all composition ranges according to differential scanning calorimetry studies. The same S-tBA copolymer series was hydrolyzed and subsequently neutralized to produce potassium salts of poly(styrene-ran-acrylic acid). Miscibility of the ionic copolymers with PPO was found to reduce to below ca. 3 mol% of the ionic content. A qualitative X-ray analysis on the ionic blend indicated that the line of demarcation for incompatibility was related to the phenomenon of onset of ion-pair association. Interaction parameter for the above miscible blends was calculated using established semi-empirical relationships. The styrene and tBA moieties were found to have strong "repulsive" type interaction leading to an even more negative interaction parameter for the S-tBA/PPO blends at higher tBA contents. The combined favorable (S/PPO) and unfavorable (S/tBA) interaction, however, did not improve miscibility for the ionic polymer blends.