Synthesis and self-assembly of chitosan-based copolymer with a pair of hydrophobic/hydrophilic grafts of polycaprolactone and poly(ethylene glycol)

Chitosan-based copolymers with binary grafts of hydrophobic polycaprolactone and hydrophilic poly(ethylene glycol) (CS-g-PCL&PEG) were prepared by a homogeneous coupling reaction of phthaloyl-protected chitosan with functional PCL-COOH and PEG-COOH, following deprotection to regenerate free amino groups back to chitosan backbone. They were characterized by 1H NMR, Fourier transform infrared and X-ray diffraction analysis. These CS-g-PCL&PEG copolymers could form nano-size self-aggregates in acidic aqueous solution without a specific processing technique, which were investigated using dynamic light scattering and transmission electron microscopy. The formed self-aggregates become smaller with weakened stability upon pH increasing. Moreover, the aggregates of copolymer with higher content of PEG and PCL grafts could remain stable for over 30 days in both acid and neutral condition. A possible mechanism was proposed for the formation of self-aggregates from CS-g-PCL&PEG and their structural changes as pH. It is warranted to find promising application of these self-aggregates based on chitosan as drug carriers.