Impact of Counter Ions of Cationic Monomers on the Production and Characteristics of Chitosan-Based Hydrogel

Chitosan-based hydrogel has received considerable interests because of its appealing properties and applications in many areas. The primary objective of this work was to produce novel cationic chitosan-based hydrogels via polymerizing chitosan with two cationic monomers of the same structure but with different counter ions [2-(methacryloyloxy)ethyl]trimethylammonium methyl sulfate (METMS) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC). Polymerization of chitosan with the cationic monomers performed under the conditions of 50 °C, 5 h, 7 pH, and 2/1 mol/mol monomer/chitosan led to chitosan-METMS and -METAC with the cationic charge densities of 3.22 and 2.88 mequiv/g, respectively. Elemental analysis, gel permeation chromatography, Fourier transform infrared, X-ray diffraction, and differential scanning calorimetry analyses were used to confirm the impact of counter ions of cationic monomers (i.e., polarizability of monomers) on their polymerization performance and the characteristics of induced chitosan-based hydrogels. Also, the results of this work postulated that the counter ions associated with the monomers could dramatically impact the water uptake and swelling properties of the generated chitosan-based hydrogels as well as their performance in adsorbing an anionic dye from a simulated solution.