Relative rate constants during the hydrolysis of syndiotactic poly(methyl methacrylate) with base

Abstract

The relative rates of appearance and disappearance of triads of monomer units during the hydrolysis of syndiotactic methyl methacrylate/methacrylic acid copolymers in aqueous solution with excess base are studied by proton n.m.r. The relative rate constants are determined from these data using a graphical method. The measured relative rates and rate constants are consistent with a mechanism wherein COO − retards the attack of OH −. There is, however, a mechanism change indicated on consumption of OH − during hydrolysis. The COOH which are then formed apparently participate in an intramolecular mechanism. The change of mechanism is accompanied by a change in copolymer statistics, i.e. from alternation tendency to block character. The lack of temperature dependence of the relative rate constants during the hydrolysis with OH − as the active species leads to the conclusion that enthalpies of activation are equal for the three reacting triads. Thus the differences found between the relative rate constants are entropic in origin.