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°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°C. MALDI-TOF mass spectrometry and Mark-Houwink-Sakurada measurements proved that under optimized reaction conditions the resulting polylactides consist of cycles.