Closed-Loop Polymer Chemistry: Designing for Efficient Monomer Recovery in Chemically Recyclable and Circular Polymers

The linear "take-make-dispose" model of conventional plastics has led to severe environmental pollution and resource depletion, necessitating a paradigm shift towards a circular economy. Chemically recyclable polymers, designed to revert to their original monomers or other valuable feedstocks at end-of-life, present a foundational solution for achieving true circularity in polymer materials. This review examines the molecular design principles underpinning such polymers, focusing on thermodynamic and kinetic strategies to balance robust performance during use with efficient depolymerization. We analyze major polymer classes enabling monomer recovery, including polyacetals, polyesters, polycarbonates, and polyolefins with low ceiling temperatures. Case studies of polydiketoenamines (PDKs), poly(γ-butyrolactone) (PγBL), and redesigned polyethylenes are discussed. Furthermore, we evaluate the integration of chemical recycling within broader technological systems, including catalysis, process engineering, and supply chain logistics. Finally, we identify key challenges in scalability, economics, material performance, and policy, outlining a multidisciplinary roadmap for transitioning from niche innovations to mainstream, sustainable materials that enable a closed-loop plastic economy.