Synthesis, characterization and degradation of poly(DL-lactide)-block-polyvinylpyrrolidone-block-poly(DL-lactide) copolymers

A new kind of A-B-A block copolymers with good biocompatibility and adjustable degradability was synthesized by ring-opening polymerization, in which DL-lactide polymerized and grew from the two ends of polyvinylpyrrolidone (PVP). The well-defined triblock structures of copolymers were characterized by GPC, H-1 NMR, FTIR and DSC. There were two pronounced glass transition temperatures which showed apparent microphase separations between hydrophilic PVP segment and hydrophobic poly(dl-lactide) (PDLLA) segments. The hydrolytic degradation of PDLLA and copolymers in phosphate buffer solution (PBS, pH = 7.4) showed that the degradation rate of copolymers apparently became faster in comparison with that of PDLLA homopolymer, and increased with increasing PVP content. The measurements through H-1 NMR and FTIR showed that the degraded fragments contained PDLLA oligomers, lactates and soluble chains composed of PVP blocks attached with short PDLLA ones.