Synthesis and rheological properties of polylactide/poly(ethylene glycol) multiblock copolymers

Ring-opening polymerization of D,L-lactide was carried out in the presence of poly(ethylene glycol), using Zn powder as catalyst. The hydroxyl-capped PLA-PEG-PLA triblock copolymers were coupled with adipoyl chloride at different molar ratios under mild conditions. N-Dimethylaminopyridine (DMAP) was used as catalyst of the coupling reaction. The resulting PLA/PEG multi-block copolymers were characterized by various analytical techniques such as IR, H-1 NMR, SEC, and DSC. Sol-gel transition properties of the multiblock copolymers were investigated by mechanical rheology. The data showed that the sol-gel transition temperature and the transition modulus increased with increasing molecular weight and the solution concentration of the multiblock copolymers.