Stereoselective association between isotactic poly(methylmethacrylate) and syndiotactic poly(methacrylic acid)

Abstract

An extensive viscometric investigation has been carried out into the stereo-association between isotactic poly(methyl methacrylate) (it-PMMA) and syndiotactic poly(methacrylic acid) (st-PMAA) in different solvents and solvent mixtures. Solvent media were classified into three types, A, B and C, depending on their decreasing ability to promote complex formation. In all ‘complexing’ solvents (type A and B), even in the best one consisting of a mixture of 83 vol % ethanol and 17 vol % water, only one of the four possible cross-combinations of tactic PMMA and PMAA can associate. This stereoselectivity was confirmed by a calorimetric (d.s.c.) study of the glass transition of the various mixtures in the bulk. The it-PMMA/st-PMAA complex, although it is weaker, resembles the well known it/st-PMMA stereocomplex in many respects. It is suggested that association occurs primarily due to stereo-complementarity of the components involving interaction of the ester groups of it-PMMA with the α-methyl groups of st-PMAA and not to hydrogen bonding via the carboxyl groups of st-PMAA.