Unravelling the effect of side chain on RAFT depolymerization; identifying the rate determining step

Abstract

Reversible addition–fragmentation chain-transfer (RAFT) depolymerization represents an attractive and low-temperature chemical recycling methodology enabling the near-quantitative regeneration of pristine monomer. Yet, several mechanistic aspects of the process remain elusive. Herein, we shine a light on the RAFT depolymerization mechanism by elucidating the effect of pendant side chains on the depolymerization kinetics. A systematic increase of the number of carbons on the side chain, or the number of ethylene glycol units, revealed a significant rate acceleration. Notably, radical initiator addition during the depolymerization of poly(methyl methacrylate) and poly(hexyl methacrylate) resulted in rate equilibration, indicating that chain activation is the rate-determining step in RAFT depolymerization. Moreover, incorporation of a low DP of hexyl monomer as the second block of poly(methyl methacrylate) led to comparable rates with poly(hexyl methacrylate) homopolymer, confirming the rate determining step. Computational investigations further corroborate this finding, revealing that chain-end fragmentation is energetically more favorable in longer-side-chain methacrylates, which accounts for the experimentally observed rate acceleration. These insights not only deepen our understanding of depolymerization but also pave the way for developing more efficient and customizable depolymerization systems.