Polylactones 3. Copolymerization of glycolide with L, L-lactide and other lactones

Numerous copolymerizations of glycolide with β-propiolactone, γ-butyrolactone, δ-valerolactone and ϵ-caprolactone were conducted either in bulk or in nitrobenzene solution at temperatures in the range of 20–150°C. Three classes of catalysts were used, namely acidic catalysts initiating cationic polymerizations, complexing catalysts operating via an insertion mechanism and true anionic catalysts. A summary of these already previously described results is presented in this work along with a detailed report on the copolymerization of glycolide and L, L-lactide. These two monomers were copolymerized in bulk at 100 or 150°C and twenty different catalysts were used in both series. The molar compositions of the resulting copolyesters were used in both series. The molar compositions of the resulting copolyesters were determined by 1H NMR spectroscopy. The possibility of 13C NMR sequence analyses is discussed for all afore-mentioned copoly(lactone)s and also for L,L-lactide/ϵ-caprolactone copoly(ester)s. DSC measurements of the glycolide/L,L-lactide copolymers are discussed in connection with the NMR spectroscopic results. Furthermore, optical rotation measurements were conducted and it was found that the optical rotation of glycolide/L,L-lactide copolymers depends on their sequence.