DL-Methionine-mediated radical-promoted cationic polymerization enabling the polymerization of allyl ethers

Abstract

Allyl ethers typically exhibit low conversion in free-radical polymerization (FRP) or afford poor control in cationic polymerization. We developed a DL-methionine (DL-Met)-mediated free-radical-promoted cationic polymerization (FRPCP) to circumvent these limitations. The photoinitiated system comprises 2-hydroxy-2-methylpropiophenone (HMPP), tetrahydrofuran (THF), and diphenyliodonium hexafluorophosphate (DPI), utilized THF to generate the active cationic species and tune solvent polarity, thereby enhancing DL-Met's efficacy. This synergistic approach achieved approximately 78% conversion of the macro-monomer poly(ethylene glycol) allyl methyl ether (PEG-AME) with a narrow dispersity (Đ = 1.23). Spectroscopic analyses confirmed the polymer structures and led to the proposal of a controllable cationic degenerate chain-transfer mechanism mediated by DL-Met. Furthermore, using this strategy, the block copolymer poly(butyl acrylate)-block-poly(poly(ethylene glycol) allyl methyl ether) (PBA-b-P(PEG-AME)) was successfully synthesized via sequential FRP and FRPCP with a Đ of 1.39. This work provides an effective strategy to overcome the intrinsically low reactivity of allyl ethers and expands their access to controlled polymerization.