Activators of anionic polymerization

Many authors have observed an acceleration of caprolactam polymerization in the presence of A-acetyl-e-caprolactam, isocyanates, thiolactones, organic sulphates, aromatic amides, benzyldioxime carbonate, arylenedicarbamoyllactams, phosphorus oxychlorides and phosphorus pen-tachloride. Activator effectiveness increases with growing substituent electronegativity in N-substituted lactams. 

Highly active molecules are therefore of the type [210] phenylphosphonyl--jV-A -biscaprolactam. 

Polymerization of 2-pyrrolidone is also activated by various A-acyl lactams, especially by iV-acetyl-2-pyrrolidone, lower lactones, CO, and JV-benzoyllac-tams [211]. 

The activation described is due to an increase in the concentration of active centres. The polymerization rate can, of course, also be enhanced by increased reactivity of the centres. To solvent-separated ion pairs and to free ions, monomers in general are added more rapidly than to contact ion pairs. When we succeed in separating the active centre ions by the addition of a strongly solvating compound, the initiation and propagation rates will be enhanced, and changes affecting the mode of addition may appear [212, 213 ]. 

For cation solvation, macrocyclic polyethers, crown ethers [214] of type 

---