Utilization of Poor RAFT Control in Heterogeneous RAFT Polymerization

Abstract

Heterogeneous reversible addition–fragmentation chain transfer (RAFT) polymerization exhibits considerable promise in polymer and colloid synthesis. During the research of RAFT polymerization, good RAFT control is always an important goal to achieve while poor RAFT control is considered to be a lack of success. Herein, we develop heterogeneous RAFT polymerization from an unusual angle by deliberately using RAFT agents with poor RAFT controllability. The utilization of poor RAFT control in heterogeneous RAFT polymerization led to the formation of samples contain high-molecular-weight block copolymers, uncontrolled homopolymers, and the unreacted macro-RAFT agent. Remarkably, uniform polymer spheres with precise size could be obtained via heterogeneous RAFT polymerization, although molecular weight distributions of the obtained polymers were broad. In-depth studies of heterogeneous RAFT polymerization mediated by a binary mixture of RAFT agents with different controllability, the RAFT agent with good controllability dominated the polymerization while the RAFT agent with poor controllability was mainly inactivated or unreacted. On the basis of the unique mechanism provided, we have been able to prepare block copolymer assemblies with rich pendant RAFT groups on the surface by one-step heterogeneous RAFT polymerization using a macro-RAFT agent with divergent RAFT end groups. The reactivity of pendant RAFT groups on the surface provides a landscape for further functionalization of block copolymer assemblies. These proof-of-concept experiments demonstrate that the utilization of poor RAFT control in heterogeneous RAFT polymerization is a promising strategy to a variety of polymer particles that are challenging to be prepared by traditional heterogeneous RAFT polymerizations.