Effect of Microstructures on the Phase Transition Behavior of P(CL-GL)-PEG-P(CL-GL) Triblock Copolymer Aqueous Solutions

Amphiphilic poly[(ε-caprolactone)-co-glycolide]-block-poly(ethylene glycol)-block-poly[(ε-caprolactone)- co-glycolide) [P(CL-GL)-PEG-P(CL-GL)] triblock copolymers with different average lengths of caproyl sequences (LCL) were synthesized by ring-opening polymerization at different temperatures. A 25% aqueous solution of the copolymer with LCL=11.0 formed a gel, owing to strong crystallinity-induced hydrophobicity at low temperature, and underwent a gel-sol transition (UCST behavior) when the temperature was increased to 40℃. In contrast, the solution of copolymer with LCL=6.7 underwent a sol-gel transition (LCST behavior) due to micelle aggregation. However, a clear sol-turbid sol phase transition was observed for the copolymer with more random microstructures (LCL=5.2).Amphiphilic poly[(ε-caprolactone)-co-glycolide]-block-poly(ethylene glycol)-block-poly[(ε-caprolactone)- co-glycolide) [P(CL-GL)-PEG-P(CL-GL)] triblock copolymers with different average lengths of caproyl sequences (LCL) were synthesized by ring-opening polymerization at different temperatures. A 25% aqueous solution of the copolymer with LCL=11.0 formed a gel, owing to strong crystallinity-induced hydrophobicity at low temperature, and underwent a gel-sol transition (UCST behavior) when the temperature was increased to 40℃. In contrast, the solution of copolymer with LCL=6.7 underwent a sol-gel transition (LCST behavior) due to micelle aggregation. However, a clear sol-turbid sol phase transition was observed for the copolymer with more random microstructures (LCL=5.2)