Synthesis and Properties of Poly(d,l-lactide-co-p-dioxanone) Random and Segmented Copolymers

Two different polymerization routes, one-step and two-step bulk ring-opening polymerizations of d,l-lactide (LA) and p-dioxanone (PDO) monermers using stannous octoate [Sn(Oct)2]/n-dodecanol as the initiating system, were employed to synthesize poly(d,l-lactide-co-p-dioxanone) P(LA-co-PDO) random and segmented copolymers with different compositions and chain microstructure. For the two-step copolymers, the average sequence lengths of the lactidyl (LLA) and dioxanyl (LPDO) units calculated from the 1H-NMR spectra were much longer than those values for the one-step copolymers with the same LA/PDO feed ratio. Corresponding to this difference in microstructure, the two-step copolymers were semi-crystalline even when the PDO content was as low as 14.5 mol%, while the one-step copolymers were completely amorphous with PDO content below 60.6 mol%. However, irrespective of polymerization route, both types of copolymers displayed a single glass transition temperature that was in a linear relation with composition. The decrease of maximum decomposition temperature of the copolymers was in accordance with the decrease of LPDO value. The mechanical and degradation properties of the copolymers were significantly affected by both the polymerization route and the chemical composition as well. In conclusion, the properties of P(LA-co-PDO) copolymers could be adjusted conveniently to meet specific applications by changing the composition and microstructure of the copolymers via different polymerization routes.