Preparation, characterization, structure, and dynamics of carboxymethyl chitosan grafted with acrylic acid sodium salt

Graft copolymerization of different vinyl monomers onto chitosan (Cs) and its derivatives can alter their properties and consequently expands their potential applications. In this study, carboxymethyl chitosan (CMCs) was prepared and characterized. Graft copolymerization of acrylic acid sodium salt (AAs) onto CMCs was accomplished by using ammonium persulphate (APS)-induced free radical polymerization in aqueous medium under nitrogen atmosphere. Occurrence of grafting was confirmed and the effects of [AAs], [APS], reaction time, and temperature on the extent of grafting were studied. The influence of grafting yield on the structure and dynamics was also investigated by using differential scanning calorimetry (DSC), two-dimensional wide-angle X-ray scattering (2D-WAXS), scanning electron microscopy (SEM), and dielectric spectroscopy. Preliminary study, using dielectric spectroscopy, was carried out to the CMCs-g-AAs copolymer with grafting percent ∼ 2900%, as an example, in a wide range of temperature (from 299 to 473 K) and frequency (from 1 × 10∼ to 1 × 10⁵ Hz). One relaxation process with Arrhenius type was detected. This process has the characteristics of a secondary relaxation process related to local chain dynamics with activation energy of 53 ± 3 kJ/mol.