Synthesis of biodegradable copolymers with low-toxicity zirconium compounds.: III.: Synthesis and chain-microstructure analysis of terpolymer obtained from L-lactide, glycolide, and ε-caprolactone initiated by zirconium(IV) acetylacetonate

Zirconium(IV) acetylacetonate [Zr(acac)(4)] is a very good initiator for the terpolymerization of glycolide with L-lactide and E-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. (C) 2002 Wiley Periodicals, Inc.