Highly efficient polymer-based nanoreactors for selective oxidation of alcohols in water

Abstract

In this study, we demonstrate the fabrication of thermo-responsive polymer-based TEMPO nanoreactors and their application in the catalytic selective oxidation of alcohols as a highly efficient and recoverable catalyst in aqueous media. First, a diblock amphiphilic copolymer NHS-P(MMA25-b-OEGMA75) consisting of poly(methyl methacrylate) (PMMA) and poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA300) with a terminal N-hydroxysuccinimide (NHS) activated ester was synthesized utilizing reversible addition–fragmentation chain transfer polymerization (RAFT) techniques. Free radical 2,2,6,6,-tetramethyipiperidinooxy (TEMPO) was then introduced into the end of the copolymer based on activated ester functionalization to afford the temperature responsive polymer-supported catalyst TEMPO-P(MMA25-b-OEGMA75). Next, core-shell TEMPO nanoreactors were formed through self-assembly of the amphiphilic block polymers in deionized water. The morphology of the nanoreactors was well characterized by dynamic light scattering (DLS) and scanning electron microscopy (SEM). The nanoreactors were then successfully applied in the selective oxidative of alcohols in water. A variety of aldehydes and ketones were achieved in excellent yields and selectivities in high reaction rates with low catalyst loading. The high efficiency in catalysis of the nanoreactors may attributed to the ideal environment where enhancing the interactions between the catalyst and the alcohol substrate, mimicking the environment of enzymes. The thermo-responsive polymer-based nanoreactors could be conveniently recovered in the temperature above the LCST of the polymer after extraction of product from the reaction mixture. This strategy provides an effective and cleaner way for the selective oxidative of alcohols in organic synthesis and industrial application.