Spiro-salen 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 sustainable plastics, its chemical recycling to monomer has been an elusive endeavour. A major obstacle for this process is that the epimerization of L-LA to meso-LA led to a loss of the original material performance of PLLA. Our robust spiro-salen 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 a spiro-salen scandium catalytic system, which promoted stereoselective and sequence-controlled polymerization of L-LA in presence of meso-LA and gave rise to 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.