Journal of Polymer Science Part A: Polymer Chemistry, Vol.45, No.4, 605-613, 2007
Poly(epsilon-caprolactone)-b-poly(ethylene glycol)-b-poly (epsilon-caprolactone) triblock copolymers: Synthesis and self-assembly in aqueous solutions
Nontoxic and biodegradable poly(epsilon-caprolactone)-b-poly(ethylene glycol)-b-poly(epsilon-caprolactone) triblock copolymers were synthesized by the solution polymerization of epsilon-caprolactone in the presence of poly(ethylene glycol). The chemical structure of the resulting triblock copolymer was characterized with H-1 NMR and gel permeation chromatography. In aqueous solutions of the triblock copolymers, the micellization and sol-gel-transition behaviors were investigated. The experimental results showed that the unimer-to-micelle transition did occur. In a sol-gel-transition phase diagram obtained by the vial-tilting method, the boundary curve shifted to the left, and the gel regions expanded with the increasing molecular weight of the poly(epsilon-caprolactone) block. In addition, the hydrodynamic diameters of the micelles were almost independent of the investigated temperature (25-55 degrees C). The atomic force microscopy results showed that spherical micelles formed at the copolymer concentration of 2.5 x 10(-4) g/mL, whereas necklace-like and worm-like shapes were adopted when the concentration was 0.25 g/mL, which was high enough to form a gel. (c) 2006 Wiley Periodicals, Inc.