Synthesis and properties of random poly(lactic acid)-based ionomers

A random poly(lactic acid), PLA, based ionomer was synthesized by copolymerizing a methacrylate-terminated PLA macromonomer and methyl methacrylate. The copolymerization kinetics were studied using 1H NMR spectroscopy and the copolymer composition was characterized by 13C NMR spectroscopy. Carboxylic acid groups were introduced into the copolymer by reacting the hydroxyl end groups of the PLA macromonomer with succinic anhydride, and the acid groups were neutralized with metal acetates to produce Na-, Ca-, and Y-PLA ionomers. Significant increases in Tg were observed for the ionomers and thermomechanical analysis indicated that the ionomers were more resistant to penetration by a weighted probe and an apparent rubbery plateau was observed above Tg. The ionomers were more hydrophilic than PLA, but relatively low water absorption could be achieved for the Ca2+-salt ionomer.