Endogenous base phosphine/dimethyl carbonate catalyzed depolymerization of poly(ethylene terephthalate)

Solvolysis of postconsumer poly(ethylene terephthalate) (PET) into monomeric feedstocks that can be recycled contributes value-added strategy to waste plastic management. Chemical route for PET recycling with sets of diols, diamines, and amino alcohols as the solvolytic reagents by endogenous basic ionic pair phosphonium organocatalyst was established. Methylation of tertiary phosphine with dimethyl carbonate produced quaternary phosphonium methyl carbonate (QPMC) catalyst of strong basic character. QPMC depolymerized PET by virtually complete conversion with 78 % up isolated yield of monomers under optimal reaction conditions of 160 °C, 2 mol% catalyst loading, and 4 h. Catalytic solvolysis mechanism with ethylene glycol was probed by NMR titrations where methyl carbonate anion coordinated to hydroxyl of ethylene glycol by H-bonding, rather than H-abstraction by the basic methyl carbonate anion, was validated.