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-la ctide with the use of a low toxic compound-Zr(acac)(4)-as initiator at a te mperature of 100 up to 150 degreesC. Copolymerization at 150 degreesC is ve ry fast and reached nearly 100% yield. The values of the copolymerization c oefficients were estimated as r(G) = 3.3 and r(L) = 0.5. The process of cha in propagation was also examined, and a significant influence of transester ification on the final structure of copolymer was observed. The microstruct ure 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 str ucture influences thermomechanical properties of the copolymers. The crysta llinity of copolymers obtained is higher than that of the formed in the pre sence of Sn(oct)(2). One of their most characteristic features concerned th eir good mechanical properties, in many cases better than those of adequate copolymers obtained with the use of tin compounds as initiators.