Anionic polymerization of caprolactam—XL. Estimation of the content of active base from the rate of polymerization and from the increase of the number of polymer molecules in activated polymerization

Abstract

At high ratios of acylcaprolactam to sodium caprolactam ( C a C s > 2·5 ), the lactam anions disappeared so quickly that the polymerization slowed down considerably even before attaining polymerization equilibrium. Under these conditions, the content of catalytically active bases was estimated from the rate of polymerization. At initial concentrations C a ≤3 Cs , the content of active base could be estimated from the change in the number of polymer molecules. At 190–250°, the concentration of active bases decreased very rapidly during the first minutes to a value C a ≤3 Cs . A further decrease in basicity is related to the increase in the number of polymer molecules by disproportionation. On the average, 1 · 5 basic groups were formed per new polymer molecule. Above 200°, the calculated effective content of active base, expressed in equivalents of sodium caprolactam, decreased during 30 min to below 1% of the initial concentration of sodium caprolactam. This value corresponds very well to the basicity of sodium carbonate or sodium salts of carboxylic acids which represent the main products of the decay of sodium caprolactam.