A Light-Driven Closed-Loop Chemical Recycling System for Polypinacols

Abstract

The development of innovative recycling strategies for polymers is crucial to addressing the rapidly growing plastic waste challenge. While thermal ground-state chemistry is the standard for closed-loop chemical recycling, the potential of photochemical excited-state chemistry remains largely unexplored. This study bridges this gap by investigating light-driven polymerization and depolymerization processes for hydroxyl-rich polymers. Through consecutive pinacol coupling reactions, a range of simple bis-aldehyde monomers is photopolymerized into well-defined polypinacols on a gram scale. These polymers exhibit excellent thermal stability, retaining their integrity up to 306 °C, with glass transition temperatures ranging from 72 to 137 °C. Using an earth-abundant cerium photocatalyst, selective cleavage of stable C─C bonds within the polypinacol backbone is achieved under visible light, efficiently regenerating the original monomer. As this approach tolerates the presence of standard commodity plastics, it presents an opportunity for orthogonal recycling methods that could help recover specific polymers from diverse plastic waste streams. The successful completion of one recycling cycle, resulting in a polymer with comparable properties to the original, highlights the significant potential and advantages of (photo)chemical recycling.