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 ( L CL ) were synthesized by ring‐opening polymerization at different temperatures. A 25% aqueous solution of the copolymer with L CL = 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 °C. In contrast, the solution of copolymer with L CL = 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 ( L CL = 5.2). magnified image