Spirosalen–scandium catalysts enable the epimerization-tolerant closed-loop circularity of poly( <scp>l</scp> -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 <i>meso</i>-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 <i>rac</i>-LA and syndioselectivity for the polymerization of <i>meso</i>-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 <i>meso</i>-LA and gave rise to the stereogradient block PLA P(<i>meso</i>-LA-<i>grad</i>-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.