Survey of alkyl methacrylate latexes as aqueous catalytic media

Abstract

Cationic polymer latexes serve as catalytic media for the hydrolysis of p-nitrophenyl esters by providing a more lipophilic environment into which these compounds can partition from the aqueous phase. The latex quaternary ammonium ions attract high local concentrations of reactive or catalytic anions into the water-swollen particles. We synthesized 32 different methacrylate and styrene latexes via a parallel synthetic route and tested their activities for the hydrolysis of p-nitrophenyl hexanoate. The most active latex is a copolymer of 75% 2-ethylhexyl methacrylate and 25% vinylbenzyl chloride that was quaternized with tributylamine. The rate of hydrolysis at 30 °C is 17 times faster using 0.6 mg mL-1 of latex in pH 9.4 borate buffer relative to control experiments that lacked polymer latex. Analysis of the kinetics shows that the latex activities depend primarily on the latex/water partition coefficients of p-nitrophenyl hexanoate. The latexes also promote the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate (6-NBIC) in aqueous media, and 0.6 mg mL-1 of the latex from 75% 2-ethylhexyl methacrylate and 25% vinylbenzyl chloride quaternized with tributylamine gave an observed rate constant 10 400 times that in water alone. The rate accelerations of 6-NBIC decarboxylation are due to both favorable partitioning into the latex and faster intraparticle rate constants.