Copolymerization of glycolide and e-caprolactone was conducted in bulk at 100 °C and in nitrobenzene or dioxane at 70,100, or 150 °C. The resulting copolyesters were characterized with respect to their molar composition by means of NMR spectra and with respect to their sequences by means of 13C NMR spectra. The results allow a classification of both copolyesters and initiators. Cationic initiators such as ferric chloride, boron trifluoride, and fluorosulfonic acid favor the incorporation of e-caprolactone, catalyze intermolecular transesterifications, and cause rapid degradation of the polyesters above 100 °C.Complexing catalysts such as zinc chloride, aluminum isopropylate, and dibutyltin dimethylate favor the incorporation of glycolide and chemical heterogeneity of first order. Furthermore, intramolecular transesterification was detected in the case of aluminum isopropylate and dibutyltin dimethylate. Anionic catalysts such as tetramethylammonium benzoate and benzyltriphenylphosphonium chloride only initiate the homopolymerization of glycolide. The polymerization mechanisms are discussed. The differential scanning calorimetry shows a close relationship between crystallinity and nature of sequences.

Numerous copolymerizations of glycolide with 6-propiolactone, y-butyrolactone, 6-valerolactone and E-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 L6L-lactide. These two monomers were copolymerized in bulk at 1 0 0 or 150 C and twenty different catalysts were used in both series The molar compositions of the resultin copolyesters were determined by iH NMR spectroscopy. The possibility of "C NMR sequence analyses is discussed for all afore-mentioned copoly(1actone)s and also for L,L-lactide/€-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-lacti.de copolymers depends on their sequence. 0252-1 997/85/lJS $0.200

Numerous copolymerizations of glycolide with P-propiolactone, y -butyrolactone or 6-valerolactone were conducted either in bulk or in nitrobenzene solution at temperatures in the range of 20 to 150 "C. Three classes of catalysts were used, namely acidic catalysts initiating cationic polymerizations, complexing catalysts initiating insertion mechanisms, and anionic catalysts. The molar composition of the copolyesters was determined from 'H NMR spectra and the sequence distribution of the comonomers from 13C NMR spectra. No reasonable copolymerization of glycolide and P-propiolactone was obtained at 20 "C in nitrobenzene, whereas all catalysts yielded copolyesters at 100 "C. In the case of glycolide/y -butyrolactone only bulk copolymerizations at 60 "C with acidic initiators were successful. Under other conditions only homopolymerization of glycolide was observed. Copolymerizations of glycolide and y-valerolactone were performed in bulk and in nitrobenzene with both acidic and complexing initiators, whereas anionic initiators only caused homopolymerization of glycolide. Acidic initiators favored the incorporation of 6valerolactone, whereas the complexing initiators favored the incorporation of glycolide. The crystallinity of the glycolide/&valerolactone copolymers was characterized by means of differential scanning calorimetry, and a good agreement with the expectations from both molar composition and sequence distribution was found.

Homopolymerisations of B-propiolactone and c-caprolactone, initiated by means of methyl trifluorosulfonate, triethyloxonium tetrafluoroborate or acetylium perchlorate, were investigated. Both ' H and 13C NMR spectra proved that the alkylating initiators yield polyesters with alkyl ester end groups, indicating a chain growth via alkyl-oxygen cleavage of the lactone. At temperatures below 100 "C cationic polymerizations initiated by alkylating reagents were found to proceed via end groups which may cause degradation due to back-biting. When ecaprolactone was reacted with excess methyl triflate, high concentration of triflate ester end groups were formed, whereas in the case of 8-propiolactone active end groups were not detectable by ' H NMR spectroscopy. Initiation with acetylium perchlorate yielded a polyester with acetate end groups. Acetate end groups were also obtained, when "living" polymers, initiated with methyl triflate, were reacted with acetic anhydride. It could be shown that the formation of acetate end groups does not indicate an electrophilic attack at the endocyclic oxygen. Furthermore, it is discussed that any experimental evidence for a cationic chain growth via acyloxygen bond cleavage is lacking.

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