About the influence of salicylic acid on tin(II)octanoate-catalyzed ring-opening polymerization of L-lactide

L-Lactide was polymerized in bulk with tin(II)2-ethylhexanoate (SnOct(2)) as catalyst and salicylic acid as cocatalyst. The Lac/Cat ratio, Cocat/Cat ratio, temperature and time were varied. Increasing Cocat/Cat ratios reduced both, polymerization rate and molecular weight. However, under optimized conditions high molar mass (Mw up to 178,000), colorless, cyclic polylactides were formed in a short time. A few polymerizations performed at 160 and 180 degrees C with the combination of SnOct(2) and silylated salicylic acid gave similar results. Neat fin(II) salicylate was prepared from SnOct(2) and used for REPs of L-lactide in bulk, but the results were not better than those obtained from combinations of SnOct(2) and salicylic acid. Furthermore, dibutyltin salicylate was synthesized and used as catalyst for polymerizations of L-lactide in bulk at temperatures varying from 102 to 160 degrees C. Cyclic polylactides with Mw's up to 40,000 were the main reaction products. At 100-102 degrees C a predominance of odd-numbered cycles was found proving a REP mechanism.