Uncontrolled polymerization that occurred during photoinitiated RAFT dispersion polymerization of acrylic monomers promotes the formation of uniform raspberry-like polymer particles

Abstract

In a typical reversible addition–fragmentation chain transfer (RAFT)-mediated dispersion polymerization, good RAFT control is usually inevitable. This characteristic leads to the formation of block copolymers with low dispersities and well-defined block copolymer nano-objects. In this study, a different type of RAFT-mediated dispersion polymerization of acrylic monomers based on poor RAFT control and photoinitiation is reported. Uniform raspberry-like polymer particles rather than well-defined block copolymer nano-objects were formed in the present case. Gel permeation chromatography (GPC) measurement indicated that a noticeable amount of uncontrolled polymers without RAFT groups was generated during the photoinitiated RAFT dispersion polymerization, promoting the formation of uniform raspberry-like polymer particles. By extracting samples at different time intervals, it was found that raspberry-like polymer particles were formed by the adhesion of small polymer particles to the surface of large smooth polymer particles. Controlled experiments demonstrated that both the use of a poly(diacetone acrylamide) (PDAAM)-based macro-RAFT agent and the use of an isobronyl acrylate (IBOA) core-forming monomer were critical for this unusual photoinitiated RAFT dispersion polymerization. We expect that this study will not only provide a facile method for the preparation of uniform raspberry-like polymer particles at high solid contents in a single step, but also provide more insights into the mechanism of photoinitiated RAFT-mediated dispersion polymerization.