High‐temperature polymerization of ϵ‐caprolactam by using as catalyst the Li, Na, or K salts derived from MAlEt4 or MOAlEt2·AlEt3 and monomer

High‐temperature polymerization of ϵ‐caprolactam by using the salts derived from MAlEt4 (where M is Li, Na, and K) and monomer as catalyst was carried out. Polymerization occurs at 140–170°C, a temperature at which alkali metal caprolactamate has almost no catalytic activity for initiation. m‐Cresol‐insoluble polymer was obtained at temperatures lower than 231°C. Formation of a m‐cresol‐insoluble polymer depends on the polymerization temperature and time, and was observed under conditions where Al(Lac)3 has no catalytic activity. All the polymers obtained by NaAl(Lac)4–n(NHBu)n (n = 1 or 2) at 202°C were soluble in m‐cresol. These trends observed in the case of MAl(Lac)4 are considered to be due to initiation by Al(Lac)3, which is a component of the catalyst used.