Photochemical post-functionalization of polystyrene enables accelerated chemical recycling

The development of molecular post-modification design strategies that enable low-temperature pyrolysis of polystyrene (PS) remains an underexplored area. The current state of the art for the pyrolysis of PS demands heating above 400°C which creates 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. We first adapted the trifluoromethylthiolation reaction to PS which involved solvent screening and reaction optimization. We observed a significant increase in the depolymerization of PS-SCF3 compared to PS across a wide range of molecular weights and consumer-grade products at 300°C. Using the Flynn-Ozawa-Wall analysis, the average apparent activation energy for the depolymerization of PS-SCF3 is ~11kJ/mol lower than pristine PS. To benchmark this protocol, we found that the pyrolysis of several consumer-grade PS-SCF3 samples at 300°C offered greater amounts of styrene compared to pristine consumer-grade PS. This study explores the possibilities of post-functionalizing the backbone of PS to depolymerize PS at faster timescales and lower temperatures to afford greater recovery of styrene, contributing towards a circular economy of plastics.