A Photofunctional Trithiocarbonate RAFT Agent Enabling Ultrafast and Fast Synthesis of Well-defined Telechelic Polymeric Photoinitiators

Abstract

A versatile and highly active photofunctional RAFT agent based on a trithiocarbonate core, capable of both controlling RAFT polymerization and initiating photopolymerization, was synthesized. The RAFT agent was derived from a bis(dimethylacetic acid) RAFT agent precursor by introducing two photoactive benzoin molecules into its carboxyl groups. This newly developed agent was successfully employed in the RAFT polymerization of acrylonitrile (AN), acrylamide (AM), styrene (St), and methyl methacrylate (MMA) monomers, producing telechelic polymeric photoinitiators with well-defined structures. Notably, the RAFT agent exhibited ultrafast polymerization rates with AN and AM, completing within minutes. While styrene (St) and MMA polymerizations were also rapid, they proceeded at a slower rate compared to AN and AM. Time-dependent ¹H NMR analysis of styrene polymerization showed an initial ultrafast reaction phase followed by a significant slowdown, suggesting the formation of dormant species. The resulting telechelic polymeric photoinitiators were further utilized for photoinduced free radical-promoted cationic polymerization (FRPCP) of cyclohexene oxide (CHO) and butyl vinyl ether (BVE), leading to the formation of ABA-type block copolymers. Comprehensive spectroscopic and analytical techniques confirmed the molecular structures of all synthesized polymers, demonstrating the effectiveness of the RAFT agent in facilitating complex polymer architectures.