Acid-enhanced RAFT depolymerization of polymethacrylates

While acidic additives have recently been shown to significantly enhance vinyl polymerizations, their effects on the reverse depropagation pathway remain completely unexplored. Herein, acid-enhanced RAFT depolymerization is introduced as a means to effectively replace thermal radical initiators with abundant acids, while also enhancing the depolymerization rate and efficiency. In particular, the addition of a simple Brønsted acid, such as acetic acid, provides up to a 7.6-fold increase in the reaction rate and more than doubles the final conversion at elevated concentrations, increasing the yield from 34% (without an acidic additive) to 75%. This accelerating effect was attributed to the acid directly lowering the activation barrier for the depropagation step, as supported by complementary density functional theory calculations. In addition, the enhanced conversion was linked to the greater end-group preservation in the presence of acid, as indicated by the retention of the UV signal during size exclusion chromatography measurements. Overall, this strategy is highly robust and versatile, operating across varied Brønsted acid strengths, such as trifluoroacetic acid and sustainable citric acid, and extending to Lewis acid catalysis at ultra-low loadings. The introduced methodology simplifies current RAFT depolymerization protocols, while revealing unique mechanistic insights concerning the role of acid during the chemical recycling of polymethacrylates.