Variable Amine Spacing Determines Depolymerization Rate in Polydiketoenamines

The design of circular polymers has emerged as a necessity due to the lack of efficient recycling methods for many commodity plastics, particularly those used in durable products. Among the promising circular polymers, polydiketoenamines (PDKs) stand out for their ability to undergo highly selective depolymerization in strong acid, allowing monomers to be recovered from additives and fillers. Varying the triketone monomer in PDK variants is known to strongly affect the depolymerization rate; however, it remains unclear how the chemistry of the crosslinker, far from the reaction center, affects the depolymerization rate. Here, we elucidate design rules for PDK acidolysis from a convergence of simulations and experiments. We demonstrate that a multi-path transition state theory approach to calculating reaction kinetics is essential to accurate modeling of small molecule hydrolysis kinetics and that the computational results match closely to experimental observations of both small molecule hydrolysis kinetics and PDK depolymerization. Notably, we found that a proximal amine in the crosslinker dramatically accelerates PDK depolymerization when compared to crosslinkers obviating this functionality. Moreover, the spacing between this amine and the diketoenamine bond offers a previously unexplored opportunity to tune PDK depolymerization rates. In this way, the molecular basis for PDK circularity is revealed and further suggests new targets for the amine monomer design to diversify PDK properties, while ensuring circularity in chemical recycling.