Preparation of thermosensitive diblock copolymers consisting of MPEG and polyesters

The dependence of the sol-to-gel transition temperature on the chemical composition of MPEG-polyester copolymer synthesized by random copolymerization of the TMC or DO with CL in the presence of HCl, with MPEG as an initiator, was analyzed. All of the copolymers formed a sol at room temperature when prepared as 20 wt % aqueous solutions. As the temperature was increased above room temperature, a sol-to-gel transition, manifesting as an increase in viscosity, was observed for all copolymers except for the diblock copolymer with a large PTMC content in the PCL segment. The sol-to-gel phase transition temperature was dependent on the type and amount of polyester segment introduced into the PCL segment. XRD and DSC analysis revealed that even in aqueous solution the diblock copolymer solutions exhibited crystalline domains that favored the formation of a gel due to the hydrophobic interactions between the hydrophobic polyester blocks.