Synthesis of cyclic poly(l-lactide) catalyzed by Bismuth Salicylates-A combination of two drugs

l-lactide was polymerized in bulk at 160 or 180 degrees C with mixtures of bismuth subsalicylate (BiSub) and salicylic (SA) as catalysts. The SA/Bi ratio and the monomer/Bi ratio were varied. The highest molecular weights (weight average, Mw) were achieved at a SA/Bi ratio of 1/1 (Mw up to 92 000 g mol(-1)). l-Lactide was also polymerized with combinations of BiSub and silylated SA, and Mw values up to 120 000 g mol(-1) were achieved at 180 degrees C. MALDI-TOF mass spectrometry and Mark-Houwink-Sakurada measurements proved that under optimized reaction conditions the resulting polylactides consist of cycles. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019