Azide-Substituted Polylactide: A Biodegradable Substrate for Antimicrobial Materials via Click Chemistry Attachment of Quaternary Ammonium Groups

Polylactide (PL) co-polymers substituted with pendant azide groups (azido-PL) were synthesized by the nucleophilic conjugate addition of 3-azido-1-propanethiol to a co-polymer of PL containing α,β-unsaturated ester units, poly(lactide-co-methylene glycolide) (ene-PL) that is obtained from the base-promoted dehydrochlorination of poly(lactide-co-chlorolactide) (chloro-PL). Alternatively, azido-PL was prepared by the treatment of chloro-PL with 3-azido-1-propanethiol without isolation of the ene-PL intermediate. The azido-PL was functionalized by copper-catalyzed [3 + 2] cycloaddition reactions with four alkynes: propargyl 4-methoxybenzoate, N,N,N-trimethyl-N-propargylammonium bromide, N,N-dimethyl-N-octyl-N-propargylammonium bromide, and N,N,N-trioctyl-N-propargylammonium bromide. Polymer adducts with N,N,N-trioctyl-N-propargylammonium bromide displayed potent antimicrobial activity both in suspension and as a polymer film.