Analysis of the kinetics of hydrolysis of p-nitrophenyl alkanoates in colloidal polymer dispersions by an ion-exchange model

Rates of hydrolyses of p-nitrophenyl acetate, hexanoate, and octanoate in b erate buffer solutions at 30 degrees C are 2.3-16.5 times faster in the pre sence of 1.2 mg mL(-1) quaternary ammonium ion exchange latex particles tha n those obtained in water alone. The latexes were constructed by emulsion c opolymerization of styrene, butyl methacrylate, or 2-ethylhexyl methacrylat e with 25 wt % vinylbenzyl chloride (VBC), 1% divinylbenzene, and 1% styryl methyl(trimethylammonium chloride) followed by quaternization of the VBC un its with either trimethylamine or tributylamine. Analysis of the kinetics a s a function of particle concentration, pH, and buffer concentration using an ion-exchange model provided partition coefficients of the p-nitrophenyl esters, intraparticle second-order rate constants, and ion-exchange selecti vity coefficients. The major contributors to the enhanced rates are the par tition coefficient favoring absorption of the p-nitrophenyl ester into the latex by a factor as large as 90 000 and intraparticle hydroxide concentrat ions up to 10 times higher than those obtained in the external water. The i ntraparticle second-order rate constants differ little from those in water.