Ring-opening polymerization of an O-carboxyanhydride monomer derived from l-malic acid

The synthesis and ring-opening polymerization (ROP) of an O-carboxyanhydride (OCA) monomer derived from l-malic acid (l-malOCA) is reported. Application of 4-dimethylaminopyridine as catalyst led to the observation of a number of undesirable side products. Investigation of different para-substituted pyridines as catalysts identified 4-methoxypyridine to have the ideal balance of activity and selectivity to enable the controlled ROP of l-malOCA. Deprotection of the benzyl ester side groups of the resultant polymers was achieved by hydrogenolysis and the resulting hydrophilic poly([small alpha]-malic acid) was observed to fully degrade within 7 days in aqueous solution.