Metal Synergistic Dual Activation Enables Efficient Transesterification by Multinuclear Titanium Catalyst: Recycling and Upcycling of Polyester Waste.

Developing highly efficient and selective catalysts for chemical recycling and upcycling of plastic waste is essential for establishing a sustainable plastics economy and reducing environmental impact. Here, we report a novel tetranuclear titanium catalyst that enables highly efficient transesterification reactions of esters and polyesters. Detailed experimental and computational studies have revealed that a bi-titanium framework facilitates a dual activation mechanism, activating both alcohol and ester simultaneously, thereby significantly enhancing the transesterification process. This catalyst demonstrated exceptionally high activity in the methanolysis of poly(ethylene terephthalate) (PET) with an activity up to 1.9 × 10 g mol  h at 0.005 mol% catalyst loading, producing polymerizable dimethyl ester and glycol monomers. Additionally, it effectively catalyzed the re-polymerization of the recovered monomers, yielding the original polyester with high molecular weight and thereby achieving an ideal circular economy for commodity polyesters. Furthermore, this catalyst can also be utilized for the efficient upgrading of PET waste via transesterification with 1,4-butanediol, polybutylene adipate, and poly(tetramethyene ether glycol), yielding engineering plastic, biodegradable polyester, and thermoplastic elastomer, respectively.