Amphiphilic block copolymers based on methoxy poly(ethylene glycol) and either crystalline or amorphous poly(caprolactone‐b‐lactide): Synthesis, solid‐state and aqueous solution characterizations

Abstract

AbstractAmphiphilic block copolymers consisting of methoxy poly(ethylene glycol) (mPEG) and either crystalline poly(caprolactone‐b‐L‐lactide) [P(CL‐LLA)]or amorphous poly(caprolactone‐b‐D,L‐lactide) [P(CL‐DLLA)], respectively, were prepared under mild conditions using dicyclohexylcarbodiimide as coupling agent. Micelles were formed from the resultant copolymers with predetermined hydrophobic and hydrophilic blocks in water by dialysis method. The composition and structure of the copolymers were characterized by 1H‐NMR, 13C‐NMR, and GPC measurements. Differential scanning calorimetry analysis revealed that the crystallization behavior of P(CL‐LLA) block is affected significantly by the molecular weight of the conjugated mPEG block, and the glass transition temperature (Tg) of P(CL‐DLLA) block is depressed by the existence of mPEG moiety in the block copolymer. The crystallization behavior was also characterized by the technique of polarized light microscopy. The hydrodynamic diameter and size distribution of micelles were determined by particle size measurements. Transmission electron microscopy images showed that P(CL‐LLA)‐b‐mPEG block copolymer self‐aggregated into thread‐like shape in water, whereas P(CL‐DLLA)‐b‐mPEG adopted a classical spherical shape. It is suggested that both the high enthalpy of crystallization and hydrophobicity of P(CL‐LLA) core‐forming blocks would be responsible for the thread‐like morphology. A possible mechanism for the thread‐like assembly morphology was also discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007