POLYLACTONES, 33 - POLYMERIZATION OF L-LACTIDE CATALYZED BY ZINC AMINO-ACID SALTS

The usefulness of the zinc salts of five different amino acids or amin o acid derivatives as polymerization catalyst of L-lactide was studied and compared. The five amino acid (derivatives) were: N-acetylglycine , N-tosylglycine, L-proline, L-pyroglutamic acid and N-acetyl-4-aminob enzoic acid. All polymerizations were conducted in bulk. Due to the lo w reactivity of all Zn catalysts a reaction temperature of 150 degrees C was needed to obtain yields around 90%. While the basic Zn prolinat e caused partial racemization, the neutral Zn salts yielded poly(L-lac tides) with 97-100% optical purity. Regardless of catalyst and reactio n conditions only moderate molecular weights were obtained.