Tripartite Hydrogen-Bonding as a Driving Force for High-Concentration Cyclization of Poly(L-lactide)

Abstract

A three-step strategy enables efficient cyclization of high-M_n PLLA at 0.5 M. Key to success is a persistent tripartite complex driven by hydrogen bonding and ion pairing. Selective intramolecular transesterification at a benzylic ester triggers ring closure, affording cyclic PLLA (M_n ≈ 26,000 g/mol) under synthetically practical conditions. SPM imaging reveals nanorings with diameters consistent with the expected contour length of cyclic PLLA chains.