Photochemical post-functionalization of polystyrene enables accelerated chemical recycling

Abstract

Molecular post-modification design strategies that enable low-temperature pyrolysis of polystyrene (PS) remain an underexplored area. Conventional pyrolysis of PS demands heating above 400 °C, creating economic barriers to commercial-scale monomer recovery. Here, we demonstrate the post-functionalization of the PS backbone with a labile C–S bond, specifically a trifluoromethylthio group (–SCF₃), to accelerate the depolymerization of PS at lower temperatures. A previously established small-molecule trifluoromethylthiolation reaction was adapted to PS through solvent screening and reaction optimization. Across a wide range of molecular weights (M_n = 1.12–110 kg mol⁻¹), including consumer-grade samples, thermogravimetric analysis demonstrates that PS-SCF₃ exhibits an onset degradation temperature 10–20 °C lower and a greater mass loss of 10–35% over 20 hours at 300 °C compared to pristine PS. Flynn–Ozawa–Wall analysis reveals that the average apparent activation energy for depolymerization of PS-SCF₃ is approximately 11 kJ mol⁻¹ lower than that of pristine PS. To assess the potential industrial relevance of this protocol, pyrolysis of several consumer-grade PS samples and their post-modified PS-SCF₃ analogues was performed at 300 °C; PS-SCF₃ samples were found to afford higher styrene recovery relative to pristine PS. This study explores the potential of backbone post-functionalization of PS as a strategy to accelerate depolymerization at lower temperatures and shorter timescales, enabling greater styrene recovery and advancing progress toward a circular economy for plastics.