Spirosalen-scandium catalysts enable the epimerization-tolerant closed-loop circularity of poly(l-lactic acid)

Although poly(l-lactic acid) (PLLA) has attracted broad interest as a sustainable plastic, its chemical recycling to a monomer has been an elusive endeavour. A major obstacle for this process is that the epimerization of l-lactide (l-LA) to meso-LA has led to a loss of the original material performance of PLLA. Our robust spirosalen-scandium complexes (Sc) showcased outstanding heteroselectivity towards ring-opening polymerization of rac-LA and syndioselectivity for the polymerization of meso-LA. Herein we report a strategy to circumvent the inevitable epimerization by exploiting an Sc catalytic system, which promoted stereoselective and sequence-controlled polymerization of l-LA in the presence of meso-LA and gave rise to the stereogradient block PLA P(meso-LA-grad-LLA) without compromising the material properties of the original PLLA. This epimerization-tolerant strategy for chemical recycling of PLLA provides an innovative pathway for the next generation of chemical recyclable polymers.