Reversible Addition-Fragmentation Chain Transfer Depolymerization of Poly(methyl methacrylate) in Toluene

Controlled depolymerizations of poly(methyl methacrylate) (PMMA) via reversible addition fragmentation chain transfer (RAFT) reach higher yields in some solvents rather than others, and the exact reasons are not fully understood. PMMA was synthesized with trithiocarbonate (TTC) and dithiobenzoate (DTB) end groups to study depolymerization in toluene, which has been reported to have a lower monomer yield than other solvents. In toluene, the depolymerization kinetics were found to have two regions: one assisted by solvent-derived impurities and another being primarily self-initiation. Using a rate order analysis, we found evidence that initiation can lead to simultaneous homolysis of the RAFT end group and the depropagation of one monomer. Additionally, DTB end groups had a greater tendency than TTC end groups to undergo elimination, terminating the active depropagating center and limiting depolymerization extent. Radical thermal initiators were added into PMMA depolymerizations in toluene, demonstrating that di-tert-butyl peroxide can increase the conversion of polymer to monomer for TTC end groups.