Graft copolymers from poly(γ-glutamic acid): Innovative macromolcular scaffolds for additive manufacturing from renewable natural resources

We report on a novel series of poly(γ-glutamic acid) (PGGA) derivatives and graft copolymers with poly(lactic acid) and poly(caprolactone), produced via an original and innovative synthetic strategy. PGGA of microbial origin is at first modified by means of a counterion exchange reaction with a lipophilic, apolar cation, obtaining a polycarboxylate salt which becomes soluble in common organic solvents. Homogeneous reaction conditions can then be applied to achieve full esterification, obtaining propargylic ester functionalities with essentially full coverage on the polymer backbone. We demonstrate that propargylic ester groups can be efficiently transformed using a click chemistry reaction, namely Copper(I)-catalyzed azide alkyne cycloaddition (CuAAC). The conjugation strategy takes advantage of modified poly(lactic acid) bearing azide functionalities as the end chains, to be used in combination with the modified PGGA. Graft copolymers are obtained efficiently, transforming the native bacterial biopolymer into a material with tailored properties for bulk scale or biomedical applications. The copolymers have been characterized regarding their chemical structure and properties using a variety of NMR and thermal characterization techniques.