Efficient Synthesis of Ultrahigh Molecular Weight Poly(methyl methacrylate) via Visible Light-Induced RAFT Polymerization in Deep Eutectic Solvent

This work investigates the potential of deep eutectic solvents (DES) to facilitate the synthesis of ultrahigh molecular weight (UHMW) poly(methyl methacrylate) (PMMA). Although several works have successfully synthesized UHMW polymers (Mn ∼ 106 g/mol) by reversible addition–fragmentation chain-transfer (RAFT) polymerization, the polymerization of hydrophobic monomers with low propagation rate constants, such as methyl methacrylate, remains challenging. In this study, we employ photoelectron/energy transfer-RAFT (PET-RAFT) polymerization with dithiobenzoate-type chain-transfer agents (CTA) in DES. The increased propagation rate and stability of CTA in DES provide a polymerization rate significantly higher than that in dimethyl sulfoxide. Furthermore, polymerization in DES exhibits two-stage polymerization kinetics. After the initial retardation stage of CTA, the polymerization rate is boosted by the gel effect, allowing the synthesis of UHMW PMMA in a reasonable time. We also analyze the effect of the reaction temperature to achieve a high polymerization rate and low molecular weight dispersity. The chain entanglement of UHMW PMMA leads to the formation of highly elastic polymer gels in DES. In short, this work suggests that the intriguing polymerization kinetics of PET-RAFT polymerization in DES enables a rapid synthesis of well-defined UHMW PMMA through photoinduced RAFT polymerization.