Zinc Catalyst for Chemical Upcycling of PLA Wastes: Novel Industrial Monomer Resource toward Poly(ester–amide)

A guanidine–zinc catalyst, which was nontoxic and highly active in the ring-opening polymerization (ROP) of polylactide (PLA) under industrial conditions, was assessed for its performance in the alcoholysis and aminolysis of PLA under mild conditions. Both techniques exhibited high conversion and yield in chemical recycling of PLA into value-added molecules, such as alkyl lactate and hydroxypropanamide derivatives, respectively. Notably, aminolysis was found to be significantly more efficient than alcoholysis, allowing >99% PLA conversion in less than 1 h and even selective degradation of commercialized PLA products in less than 2 h (>99% conversion). Additionally, the unprecedented approach employing diols and diamines as nucleophiles has been utilized to synthesize new, repolymerizable diol monomers, which upon reaction with dicarboxylic acids yield controllable poly(ester–amide) (PEA) structures with tunable Tg values ranging from 12.8 to 117.6 °C. We have developed efficient solutions for alcoholysis and aminolysis of polyesters and have successfully created a technological process to transform PLA from "old" to "new".