Synthesis of Poly[(lactic acid)-alt- or co-((S)-aspartic acid)] from (3S,6R,S)-3-[(Benzyloxycarbonyl)methyl]-6-methylmorpholine-2,5-dione

Poly[(lactic acid)-alt-((S)-β-benzyl aspartate)] was synthesized via ring-opening polymerization of (3S,6R,S)-3-[(benzyloxycarbonyl)methyl]-6-methylmorpholine-2,5-dione (Cyclo[Lac-Asp(OBzl)]) in the presence of Sn(oct)2 as a catalyst at 140°C. Poly[(lactic acid)-co-((S)-β-benzyl aspartate)] was obtained via copolymerization of Cyclo[Lac-Asp(OBzl)] with D,L-lactide under the same conditions. The protective benzyl groups of these copolymers were completely removed by catalytic hydrogenation to give biodegradable poly[lactide-alt- or co-((S)-aspartic acid)]. Poly[lactide-alt- and co-((S)-aspartic acid)] are amorphous polymers. The glass-transition temperature of the copolymers after deprotection is higher than that of copolymers before deprotection.