Poly(ethylene glycol)-polyester diblock copolymers have been widely developed as temperature-responsive hydrogels due to their biodegradability and excellent biocompatibility. The polyester diblock copolymers have crystallinity due to the hydrophobic aggregation that enables sol-to-gel phase transition by temperature. However, polyester diblock copolymers have a critical limitation of the absence of suitable functionality, which may cause insufficient delivery of bioactive molecules such as drugs, peptides and hormones. In this study, polyester diblock copolymers with functionalizable pendant groups were prepared and evaluated as temperature-responsive hydrogels.
In Chapter 2, functionalized monomer (CL-OBn) was synthesized and polymerized with ε-caprolactone (CL) by using methoxy polyethylene glycol (MPEG) in the presence of HCl·Et2O as a monomer activator. MPEG-b-poly(ε-caprolactone) (MC) with benzyl pendant groups (MC-OBn) was successfully obtained, and then deprotection of the benzyl groups provided MC with hydroxyl pendant groups (MC-OH). The sol-to-gel phase transition of the MC-OBn and MC-OH diblock copolymers was found to depend on the type and amount of pendant groups.
In Chapter 3, we prepared MC with cationic (MC-NH2) and anionic (MC-COOH) pendant groups and evaluated the formation of temperature-responsive hydrogels via the electrostatic interaction of ionic pendant groups. The electrostatic interactions were confirmed by mixing the hydrogels of MC-COOH and MC-NH2 diblock copolymers. In addition, the suspensions of ionic hydrogel with counter ionic electrolytes exhibited sol-to-gel phase transition to depend on the identities and concentration of electrolytes as the crosslinking agent.
In conclusion, polyester diblock copolymers with various pendant groups were successfully prepared and examined sol-to-gel phase transition by temperature. These results explain that the novel polyester diblock copolymers can be served as temperature-responsive hydrogels for biomedical applications.
