Chitosan-graft-poly(ε-caprolactone)s: An optimized chemical approach leading to a controllable structure and enhanced properties

Abstract

A novel synthetic approach was developed for the controllable modification of chitosan (CS) with poly(ε-caprolactone) (PCL). 6-O-Triphenylmethyl- chitosan (TMCS) was synthesized as a highly soluble intermediate in organic solvents to facilitate an efficient grafting reaction of PCL onto CS in a homogeneous reaction medium. Subsequently, the syntheses of CS-g-PCL copolymers with different degrees of substitution (ds) and various chain lengths of PCL (number-average molecular weight = 1200-11,000) were carried out by a coupling reaction between the carboxylic terminal groups of PCL chains and the amino groups of TMCS. The successful grafting reaction was confirmed by GPC measurements, which indicated that the products were graft copolymers rather than physical blends. The ds, defined as the number of PCL chains per saccharide unit, of the graft copolymers could be adjusted simply by changes in the molar feed ratios of PCL to CS, and graft copolymers with different ds values ranging from 0.28 to 0.49 were synthesized, as calculated by 1H NMR and elemental analysis. DSC and X-ray measurements showed that the melting temperature and enthalpy of the PCL grafts of these graft copolymers could be adjusted by the ds and the chains length of PCL, respectively. Meanwhile, the CS-g-PCL copolymers exhibited better solubility in various solvents, such as in chloroform for some of the resultant graft copolymers, than the original CS. Finally, nanoparticles of 100-200 nm, having hydrophobic PCL domains and cationic hydrophilic surfaces, were obtained through the self-assembly of the copolymers in selective solvents. These types of graft copolymers have great potential in various applications, such as targeted drug and gene delivery as well as tissue engineering. © 2007 Wiley Periodicals, Inc.