Ring‐Expansion Copolymerization of l‐Lactide and Glycolide

Abstract

Abstract1:1 Copolymerizations of glycolide (GL) and l‐lactide (LA) are performed in bulk at 100 C and at 160 C with four cyclic tin catalysts. The resulting copolyesters are characterized by size exclusion chromatography measurements, 1H and 13C NMR spectroscopy and by MALDI‐TOF mass spectrometry. At 160 °C and longer reaction time (22 h), nearly complete conversion of both monomers is achieved, and cyclic copolymers with nearly random sequences are formed. At shorter times (0.5–3.0 h, depending on catalyst) the conversion of LA is incomplete, and only cyclics having even numbers of lactyl units are obtained. At 100 C and 22 h again cycles mainly consisting of even numbered lactyl units are formed, but with even and odd numbers of glycolyl units. Copolymerization of lactide at 160 C with small amounts of GL show that formation of high Tm crystallites (Tm > 190 C) is hindered even when only >2% of GL is added. For polyglycolide containing a smaller amount of lactide complete solubility in hexafluoroisopropanol is only observed around and above 20 mol% of lactide.