Catalytic activity of a thermosensitive hydrophilic diblock copolymer-supported 4-N,N-dialkylaminopyridine in hydrolysis of p-nitrophenyl acetate in aqueous buffers

Abstract

This article reports on the synthesis of a thermosensitive hydrophilic diblock copolymer with the thermosensitive block containing a catalytic 4-N,N-dialkylaminopyridine and the study of the effect of thermo-induced micellization on its catalytic activity in the hydrolysis of p-nitrophenyl acetate (NPA). The block copolymer, poly(ethylene oxide)-b-poly(methoxydi(ethylene glycol) methacrylate-co-2-(N-methyl-N-(4-pyridyl)amino)ethyl methacrylate), was synthesized by ATRP. The critical micellization temperatures (CMTs) of this block copolymer in the pH 7.06 and 7.56 buffers were 40 and 37 °C, respectively. The polymer was used as the catalyst for the hydrolysis of NPA. We found that below CMT, the logarithm of initial hydrolysis rate changed linearly with inverse temperature. With the increase of temperature above CMT, the plot of logarithm of reaction rate versus 1/T leveled off, i.e., the hydrolysis rate did not increase as much as anticipated from the Arrhenius equation. This is likely because the reaction rate at temperatures above CMT was controlled by mass transport of NPA from bulk water phase to the core of micelles where the catalytic sites were located.