Hydrolysis of polyacrylamide and investigation of characteristics of its hydrolyzed forms
Abstract
Processes of polyacrylamide hydrolysis were investigated. It was found that the reaction rate at all temperature intervals (50-98°C) is high at the initial stage and decreases with the increase of the conversion of the initial macromolecule. The slowing down of the rate can be explained by the increase of negative charges along the macromolecule chain, i.e., carboxyl groups, which impede interaction due to electrostatic repulsion with OH− ions. Investigation of the effect of the nature of the hydrolyzing cation on the product yield showed that in the region of low alkali concentration, i.e., at MeOH/PAA ratios from 0.5 to 1, an increase in the degree of hydrolysis is observed in the order Li+<Na+=K+. If the relative molecular weight of the initial polyacrylamide sample is 685000 Da, hydrolysis at temperatures from 50 to 80°C contributed to an increase in molecular weight, while further increase, on the contrary, reduced it. Presumably, at high temperatures (98°C), -C-C-bonds break along the main chain and oxidation occurs. Due to this, these samples are characterized by high acid number at relatively low values of their solution viscosity.