Synthesis of Biodegradable Copolymers with the Use of Low Toxic Zirconium Compounds. 1. Copolymerization of Glycolide with l-Lactide Initiated by Zr(Acac)4

The paper describes a new method of copolymerization of glycolide with l-lactide with the use of a low toxic compoundZr(acac)4as 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 rG = 3.3 and rL = 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.