TEMPO-Functionalized Nanoreactors from Bottlebrush Copolymers for the Selective Oxidation of Alcohols in Water.

Abstract

Polymeric nanoreactors in water fabricated by the self-assembly of amphiphilic copolymers have attracted much attention due to their good catalytic performance without using organic solvents. However, the disassembly and instability of relevant nanostructures often compromise their potential applicability. Herein, the preparation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-containing nanoreactors by the self-assembly of amphiphilic bottlebrush copolymers has been demonstrated. First, a macromonomer having a norbornenyl polymerizable group was prepared by RAFT polymerization of hydrophobic and hydrophilic monomers. The macromonomer was further subjected to ring-opening metathesis polymerization to produce an amphiphilic bottlebrush copolymer. Further, TEMPO, as a catalyst, was introduced into the hydrophobic block through the activated ester strategy. Finally, TEMPO-functionalized polymeric nanoreactors were successfully obtained by self-assembly in water. The nanoreactors exhibited excellent catalytic activities in selective oxidation of alcohols in water. More importantly, the reaction kinetics showed that the turnover frequency is greatly increased compared to that of the similar nanoreactor prepared from liner copolymers under the same conditions. The outstanding catalytic activities of the nanoreactors from bottlebrush copolymers could be attributed to the more stable micellar structure using the substrate concentration effect. This work presents a new strategy to fabricate stable nanoreactors, paving the way for highly efficient organic reactions in aqueous solutions.