Alkaline hydrolysis of polyacrylonitrile, 2. On the product swelling

The swelling capacities of alkali hydrolyzed polyacrylonitrile in water Qw and in 0.9 wt.-% NaCl aqueous solution Qs were measured. Using these data the fraction of crosslinked units is estimated to vary from 0.8 to 1.6% for different samples. The analysis of Qs dependence on Qw is proposed as a method to estimate the degree of polymer network ionization α. The α value is found to be approximately 0.36 for all samples at the degree of neutralization 0.49–0.70. This indicates that a significant part of counterions does not affect the swelling, being bound by polyions. The influence of the conditions of hydrolysis (polymer/alkali and water/ethanol ratios) on the swelling properties of the product and the nature of crosslinks are discussed. Interchain interaction of an amidine group and an acrylonitrile unit resulting in a formation of β-diketone-like structure is proposed to explain the crosslinking. Kinetic measurements were carried out to estimate the ratio of the initial rate constants for the polyacrylonitrile and polyacrylamide alkaline hydrolysis which was found to be of order 10–1.