Abstract
l-Lactide was polymerized in bulk with tin(II)2-ethylhexanoate (SnOct2) 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 °C with the combination of SnOct2 and silylated salicylic acid gave similar results. Neat tin(II)salicylate was prepared from SnOct2 and used for REPs of l-lactide in bulk, but the results were not better than those obtained from combinations of SnOct2 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 °C. Cyclic polylactides with Mw’s up to 40,000 were the main reaction products. At 100–102 °C a predominance of odd-numbered cycles was found proving a REP mechanism.
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