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 multiblock copolymers were characterized by various analytical techniques such as IR, 1H 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. [Graph: see text] Variation of storage modulus (G') and loss modulus (G'') as a function of temperature for a 20% sample of MB3.