Structure and properties of vinylpyrrolidone-chitosan graft copolymers and homopolymer mixtures

The structure of vinylpyrrolidone-chitosan graft copolymers and homopolymer mixtures was studied by the methods of X-ray analysis and atomic force microscopy. As was found, the graft copolymers have an amorphous structure, whereas the mixtures contain a crystalline fraction. Films of chitosan-vinylpyrrolidone mixtures and copolymers demonstrated enhanced strength, plasticity, and moisture absorption in comparison with a pure chitosan. In the synthesis of the graft copolymers, the specific features of free-radical polymerization of vinylpyrrolidone in acetic acid solutions of chitosan were revealed. The enthalpies of polymerization, hydrolysis, and sorption were calorimetrically determined for vinylpyrrolidone; they were -70.0, -28.0, and -6.9 kJ/mol, respectively.