Catalysts for the Glycolysis of PET: High-Throughput Experimentation to Design a Thermoresponsive Approach

Abstract Plastics are indispensable in modern society, yet their end-of-life management remains challenging. Poly(ethylene terephthalate) (PET), widely used in packaging and textiles, contributes significantly to plastic waste due to limited recyclability. Chemical recycling via glycolysis enables depolymerization of PET into bis(2-hydroxyethyl) terephthalate (BHET), which can be repolymerized into virgin-quality PET. This work introduces thermoresponsive organocatalysts that operate homogeneously at elevated temperatures but reversibly precipitate upon cooling in ethylene glycol, enabling energy-efficient separation and reuse. High-throughput experimentation (HTE) and an eco-sustainability assessment were used to evaluate combinations of organobases and phenol-functionalized polymers. Through systematic elimination, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) supported on poly(4-vinylphenol) (PVPhenol) emerged as the lead system, demonstrating good catalytic activity, BHET selectivity, straightforward synthesis, and an upper critical solution temperature-type (UCST) behavior. Kinetic modeling revealed two distinct shrinking-core regimes, with apparent activation energies of 86.49 and 112.87 kJ mol–1. Further analysis showed that in situ formation of terephthalic acid and related acidic species led to progressive DBU protonation, suppressing UCST behavior and reducing catalytic performance. This irreversible loss of thermoresponsiveness hindered catalyst recovery. Overall, the study highlights the value of HTE-guided catalyst discovery and key design considerations for next-generation thermoresponsive systems for PET chemical recycling.