(629c) On Modeling the (De)Polymerization of Hyperbranched Polyesters

Hundreds of millions of tonnes of plastic are produced each year, only a fraction of which is currently recycled. This enormous quantity of polymer waste represents both a significant environmental challenge as well as an opportunity to recover valuable chemicals or materials. Many of the polymers produced today have been optimized for properties relevant to their primary use, without regard to their ability to be depolymerized or recycled. Polyesters synthesized from lactones have recently shown promise as materials that can undergo depolymerization at their end-of-life. A particularly exciting hyperbranched polyester synthesized from a lactone monomer was shown to depolymerize with >90% conversion to monomer with undetectable side products. However, it remains unknown how the reaction kinetics depend on the structure of the polymer chains and the functional groups present on each chain unit. We developed a mechanistic kinetic model for the reversible growth of this hyperbranched polyester system to gain insight into the growth mechanism, polymer structure, and its depolymerization potential. Kinetic Monte Carlo (kMC) was used to track chain-specific detail, including the full structure of each polymer chain. Kinetic parameter estimates were derived from density functional theory (DFT) calculations. Transport limitations were accounted for by using an effective rate constant that was a function of both the intrinsic kinetics rate constant and a chain-length dependent transport rate constant, and it was found that this further improved the model’s ability to capture the trends in the experimental data. The model was then used to probe characteristics of the system that are not readily explored by experiment itself, such as catalyst coverage and how the dominant growth mechanism shifts over the course of the reaction. This model lays the foundation for future design and study of hyperbranched polyesters derived from lactones, leading to new readily depolymerizable polymers.