Head-to-head vinyl polymers. VII. Hydrolysis of head-to-head poly(methyl acrylate)

Head-to-head (H–H) and head-to-tail (H–T) poly(methyl acrylate)s (PMAs) were hydrolyzed in a mixture of acetone and water (4:1 by volume) at 30°C by using various alkali hydroxides as catalysts. For comparison, the H–T copolymer with 26% H–H units, dimethyl succinate (DMS), dimethyl glutarate (DMG), and dimethyl adipate (DMA) as model compounds were also hydrolyzed. It was found that the hydrolyses of all PMAs proceeded autocatalytically; i.e., the rates increased as a function of the reaction time. Both the initial rate constant k₀ and the autoaccelerating effect observed markedly depended on the structures of polymer chains and they decreased with increasing of the H–H sequences. The molecular weights of either H—H or H—T PMA did not show remarkable changes in either k₀ value or accelerating effect. The k₀ values were almost independent of the kinds of bases and were calculated to be 0.06 and 0.18 L mol^?1 min^?1 for H–H and H–T PMA, respectively. On the other hand, the autoaccelerating effect decreased in the order NaOH ? KOH > LiOH > CsOH for H–H PMA and NaOH > LiOH > KOH > CsOH for H–T polymer. When the ratio of acetone to water increased, the k₀ value was found to decrease, whereas the accelerating effect increased. The results obtained are described and discussed.