Connecting polymer synthesis and chemical recycling on a chain-by-chain basis: a unified matrix-based kinetic Monte Carlo strategy

One of the challenges faced by modern society is the realization of a circular economy for polymer products. A bottleneck is the understanding of (co)polymer synthesis and degradation routes on a chain-by-chain basis, as the location of specific functional groups or structural defects determines the distributed chemical nature of the macrospecies involved and thus the reaction possibilities and macroscopic properties. Here, we present a unified matrix-based elementary step driven kinetic Monte Carlo (kMC) strategy to fully connect polymer synthesis and subsequent degradation at the molecular level, aiming at the recovery of the original monomer or a product spectrum of oligomers either degradable or upcyclable into high value-added products. This kMC strategy is illustrated for radical polymerization with methyl methacrylate (MMA) as the main monomer, selecting two case studies: (i) radical polymerization of MMA and the subsequent thermal degradation back to this monomer; and (ii) radical copolymerization of MMA with 2-methylene-1,3-dioxepane (MDO) and the subsequent hydrolysis of the resulting poly(MMA-MDO) toward biodegradable oligomers. For the first case study, it is shown that the shape and location of the log-molar mass distribution strongly affects the degradation efficiency. For the second case study, it is highlighted that the inherent molecular heterogeneity of copolymers strongly defines the framework in which degradation synthesis routes can be exploited. Polymer synthesis and subsequent depolymerisation/degradation are linked at the molecular level.