Amino acid vinyl esters: A new monomer palette for degradable polycationic materials

Toward the goal of developing degradable polycationic materials with tunable backbone charge densities and hydrophilicities, we report the optimized syntheses and polymerization activities of a series of N-Boc-protected amino acid O-vinyl ester (BAAVE) monomers derived from Boc-protected glycine, alanine, valine, and proline. The homopolymerization and copolymerization behaviors of these monomers under thermally initiated conventional free radical polymerization conditions are studied. By conducting copolymerizations of (N-tert-butoxycarbonyl)glycine vinyl ester (BGVE) with vinyl acetate (VAc) at various feed ratios and by analyzing the compositions of the resulting polymers produced at 88°C using 1,1′-azobis(cyclohexane-1-carbonitrile) (V-40) initiation, we find that the reactivity ratios are r _BGVE = 1.61 ± 0.12 and r _VAc = 0.82 ± 0.07. Treatment of poly(VAc-co-BAAVE) with neat CF ₃COOH selectively unmasks the Boc-protected amine functionalities to furnish cationic poly(VAc-co- AAVE·CF ₃COOH) copolymers. Alternatively, treatment of these random copolymers with methanolic HCl results in the complete hydrolysis of both the Boc-protecting groups as well as the acetate esters, enabling access to well-defined, hydrophilic, polycationic amino acid ester-functionalized poly(vinyl alcohol) materials.