ACID HYDROLYSIS OF ISOTACTIC AND SYNDIOTACTIC POLY (METHYL METHACRYLATE)

Isotactic and syndiotactic poly(methyl methacrylate) (PMMA) were partially hydrolyzed in concentrated sulfuric acid. The distribution of the carboxylic acid residues in the isotactic copolymers was determined by thermally dehydrating the acid to cyclic anhydride groups and comparing the yield of anhydride with the conversion calculated for random, block, and random pair distribution models; a strong tendency toward blocking was found. The proton resonance spectra of similar samples of the syndiotactic copolymers, reported previously by Klesper, indicated a random sequence distribution. The difference in the distribution of the carboxylic acid units in materials derived from the polymers suggested a mechanistic explanation for the differences in the maximum degree of hydrolysis and the relative rates of the hydrolysis reactions. The failure of syndiotactic PMMA to hydrolyze beyond about 85% could be explained by the deactivation in otherwise random hydrolysis of ester units flanked on both sides by pairs of methacrylic acid residues (or anhydride rings). The auto-catalytic effect demonstrated by the formation of blocks of acid residues during the hydrolysis of ester groups in the isotactic polymer is shown to account for both the faster rate and the completion of hydrolysis. © 1969, American Chemical Society. All rights reserved.