Chemical Upcycling of Poly(Lactic Acid) Waste Into Lactyl-Based Diols for the Synthesis of New Polyesters.

The development of efficient catalytic strategies for the chemical recycling and upcycling of poly(lactic acid) (PLA) is of great importance for advancing sustainable polymer technologies and promoting a circular plastics economy. Herein, we describe the selective alcoholysis of PLA promoted by a commercial titanium alkoxide and a phenoxy-imine pyridine zinc complex using various diols, leading to the formation of novel lactyl-based intermediates that were employed in subsequent polycondensation reactions with dicarboxylic acids. Alcoholysis reaction of PLA in the presence of ethylene glycol, 1,4-butanediol, cis-2-butene-1,4-diol and 3-allyloxy-1,2-propanediol afforded novel lactyl-containing diols, which were successfully reacted with adipic acid to produce a series of novel copolyesters. Structural characterization by one- and two-dimensional NMR spectroscopy confirmed the effective incorporation of lactyl units into the polymer backbones. Thermal analyses revealed that the introduction of lactyl moieties influences the crystallinity and thermal behavior of the resulting materials, generally leading to amorphous polymers. This approach demonstrates a straightforward and versatile route for the valorization of PLA waste into novel functional building blocks for the synthesis of potentially biodegradable polyesters with a variety of chemical features.