The paper describes a new method of copolymerization of glycolide with l-lactide with the use of a low toxic compoundZr(acac)4as initiator at a temperature of 100 up to 150 °C. Copolymerization at 150 °C is very fast and reached nearly 100% yield. The values of the copolymerization coefficients were estimated as r G = 3.3 and r L = 0.5. The process of chain propagation was also examined, and a significant influence of transesterification on the final structure of copolymer was observed. The microstructure of the chain was determined by NMR spectroscopy. It was found that more segmental structure had been formed as compared with the structure of the copolymer obtained in copolymerization initiated by tin compounds. This structure influences thermomechanical properties of the copolymers. The crystallinity of copolymers obtained is higher than that of the formed in the presence of Sn(oct)2. One of their most characteristic features concerned their good mechanical properties, in many cases better than those of adequate copolymers obtained with the use of tin compounds as initiators.

A series of copolymers with various compositions were synthesized by bulk ring-opening polymerization of glycolide and epsilon-caprolactone, using stannous (II) octoate or zirconium (IV) acetylacetonate as initiator. Reaction time and temperature were varied so as to induce different chain microstructures. The resulting copolymers were characterized by (1)H NMR, SEC, DSC, and X-ray diffraction. The average lengths of glycolyl (L(G)) and caproyl sequences (L(C)) and the degree of randomness (R) were calculated and compared to the values of completely random chains. The concentration of CGC sequences was also obtained which resulted from transesterification reactions. Data showed that stannous (II) octoate leads to less transesterification than zirconium (IV) acetylacetonate, and lower temperatures lead to less transesterification than higher ones. The copolymers exhibited a more or less blocky chain structure because of the reactivity difference between glycolide and epsilon-caprolactone. The crystalline structure and thermal properties depend on both the composition and the chain microstructure. PGA- and PCL-type crystallites were obtained for copolymers with intermediate compositions.

Zirconium(IV) acetylacetonate [Zr(acac)4] is a very good initiator for the terpolymerization of glycolide with L‐lactide and ϵ‐caprolactone. The microstructure of the obtained terpolymer was determined by NMR spectroscopy and then compared with terpolymers obtained in the presence of stanous(II) octoate [Sn(oct)2]. Samples obtained with Zr(acac)4 were characterized by a segmental‐chain microstructure. Apart from relatively long lactidyl microblocks, there were also segments made of random copolymer of glycolide with lactide. Such a structure is formed as a result of strong transesterification caused by active caproyl chain endings attacking the glycolidyl groups. Domination of this type of transestrification is shown. The growth of terpolymer chains and the influence of transesterification on gradual changes of the microstructure of the forming terpolymer chain were examined. Significant differences among glycolide, lactide, and the least reactive caprolactone were observed. The results of differential scanning calorimetric examinations of the obtained terpolymers are presented. Differences between the structures of random terpolymers obtained during terpolymerization initiated by Sn(oct)2 and those obtained by Zr(acac)4 influence their thermal properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3129–3143, 2002