Anionic polymerization of caprolactam—LII. Effect of reaction conditions on the content of acidic and basic groups in the polymer

The concentration of acidic groups in water-extracted polymers at rather short reaction times and temperatures of about 200° is predominantly determined by the initial concentration of activator; at higher temperatures and long reaction times, the concentration of acidic groups depends in the first place on the initial concentration of sodium caprolactam as initiator. The acidic groups are not composed of carboxylic groups only; some of the groups are due to the hydrolysis of labile structures during extraction of the polymer with boiling water. While the concentration of acidic groups in the polymer approximately attains the initial concentration of sodium caprolactam, the concentration of basic groups in the polymer may exceed this value several times. The rate of formation of basic groups is proportional to the instantaneous concentration of the strong base.