“Clickable” polylactic acids obtained by solvent free intra-chain amidation

An innovative solvent- and catalyst-free procedure for the grafting of acetylene groups on polylactic acid (PLA) backbone is reported, using propargylamine as alkyne donor. The synthetic protocol was tested at different PLA/propargylamine molar ratio and the efficiency was determined in terms of functionalization degree and molecular weights. The engineering of PLA by the green protocol introduces alkyne moieties and generates free hydroxyl groups that are exploited to increase the alkyne functionality by treatment with pent-4-ynoic anhydride. Alkyne-grafted PLA derivatives are useful building blocks for access to a variety of functionalized polymers by Cu(I)-catalyzed cycloaddition reaction (CuAAC) with azides derivatives. As a proof of principle, methoxypolyethylene glycol azide and azide-fluor 545 are selected as models of hydrophilic polymer and fluorescent probe, respectively.