Preparation, characterization and aggregation behavior of amphiphilic chitosan derivative having poly (l-lactic acid) side chains

The amphiphilic graft copolymer using chitosan (CS) as hydrophilic segment and poly (l-lactic acid) (PLLA) as hydrophobic segment was prepared through a protection-graft-deprotection route. PLLA macromonomer which molecular weight (M¯n) and polydispersity index (PDI) are 4267, 1.30, respectively, reacted with hydroxyl groups on phthaloylchitosan (PHCS) regionselectively. The graft reaction was carried out in homogeneous system using N,N-dimethylformamide (DMF) as solvent. The grafting content increases with the PLLA/PHCS ratio and reaction time. Furthermore, the grafting content soared from 80 to 90 °C and then leveled off. Under the present preparation method, it varied from 43.4% to 342.6%. The aggregation of the copolymers in aqueous solutions was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated both hollow and solid spherical micelles were present in aqueous solutions. The ratio between the two kinds of spheres involved with the grafting content of PLLA. The number of hollow spheres reduced with the increase of the grafting content.