(388f) In silico Strategies for Achieving Polymer Circularity: Redesigned Monomers, Advanced Catalysts, and Mechanistic Understanding

Chemical recycling to monomer (CRM) offers a potential waste management solution by reforming constituent monomers for subsequent re-polymerization.¹ While a general challenge lies in the inefficiency of depolymerization, optimization of ring-opening polymerization (ROP) and its associated ring-closing depolymerization (RCDP) holds promise for sustainability.^2,3 However, ROP and RCDP encounter difficulties when there are heterocycles that incorporate aromatic or rigid substituents. To address this challenge towards more sustainable plastics, two promising approaches emerge: developing new catalysts for depolymerization, with solvent-free systems being optimal, and redesigning the monomers with the properties needed for intrinsically circular polymers (iCP).^3,4

Recent advancements in lanthanide complex catalysis have facilitated efficient depolymerization of nylon-6 to ε-caprolactam (7LM) under mild conditions.⁵ We have recently expanded the application for other polyamides and poly(cyclohexene carbonate). Nevertheless, existing depolymerization methods do not fully address the recyclability limitations of certain plastics, primarily due to their high ring strain and ceiling temperature.⁶ This has spurred interest in redesigning monomers for better recyclability in polymers such as nylon-6 and polyhydroxyalkanoates (PHA), aiming for novel, more recyclable variants. Utilizing density functional theory (DFT), we delved into the thermodynamic and kinetic aspects of circular polymers, uncovering how enthalpy, entropy, and confinement influence polymer-catalyst interactions. In collaboration with experimental research, our simulations have provided crucial insights for catalyst design and experimental optimization, facilitating the development of high-yield, regioselectively products. This effort supports the in silico development of new iCPs, employing high-throughput analysis for T_c simulation, thus marking a significant step forward to achieve the broad design landscape of circular polymers.⁴

References

(1) Nat. Rev. Mater. 2020, 5 (7), 501–516.

(2) Chem. Rev. 2017, 117 (3), 1319–1406.

(3) Chem 2021, 7 (11), 2896–2912.

(4) Cell Rep. Phys. Sci. 2024, 101910.

(5) Chem 2024, 10 (1), 172–189.

(6) Angew. Chem. Int. Ed. 2024, e202320214.