Polymer Bulletin, Vol.72, No.8, 2075-2087, 2015
Michael reaction of chitosan with acrylamides in an aqueous alkali-urea solution
Michael reaction of chitosan with acryl reagents in acidic media is a facile method to introduce functional groups; however, when acrylamide (AAm) is used only a low degree of substitution was achieved. Here, the reaction was carried out in a new solvent, aqueous LiOH/urea solution. In the alkaline media, hydroxyl groups at the C-6 position, instead of amino groups at the C-2 position, act as Michael donor. The introduced amide groups continue to hydrolyze to give carboxylate groups. The reaction is faster, and the total degree of substitution is higher than the one achieved in acidic media, despite that the reaction temperature is lower and the reaction time is shorter. The total degree of substitution and hydrolysis percentage increases with increasing reaction time and elevated temperature. Increasing the feeding molar ratio of AAm to chitosan increases the total degree of substitution, but reduces hydrolysis percentage.