The effects of molecular structure on sol-to-gel transition of biodegradable poly(depsipeptide-co-lactide)-g-PEG copolymers.

We report on the effects of number and length of PEG chains in poly(depsipeptide-co-DL-lactide)-g-poly(ethylene glycol) (P(DG-DL-LA)-G-PEG) copolymers on their sol-to-gel transition behavior. The graft-type copolymer is suitable for the systematic study of the effects of molecular structure and hydrophilic/hydrophobic balance on its sol-to-gel transition. We prepared various P(DG-DI-LA)-G-PEG copolymers through coupling reactions between the pendant carboxylic acid groups of P(GD-DL-LA) and the end hydroxyl group of MeO-PEG having various molecular weights. Temperature-responsive sol-to-gel transition of the obtained copolymer solution in phosphate-buffered solution (pH 7.4, ionic strength = 0.14) was investigated by the test tube inverting method and rheological measurements. P(GD-NI.-LA)-G-PEG copolymer prepared from higher molecular weight PEG showed higher sol-to-gel transition temperatures compared with the copolymers prepared from lower molecu-lar weight PEG, although these copolymers have similar weight content of PEG (23-24 wt.%). Similar trends were observed for groups of copolymers whose PEG contents were 27 or 30 wt.%. These results are informative for providing strategies on rational design of thermo-gelling polymers. [ABSTRACT FROM AUTHOR]