Effect of the cation on the formation of keto structures during activated anionic polymerization of lactams

During the polymerization of caprolactam (activated with N-benzoylcaprolactam at 225°C) the content of the keto structures increases with decreasing ionization potential of the metal whose lactamate was ·used as initiator in the series Ba + + < BrMg + ~ Li + < Na + ~ K + ~ Cs +. The order of the polymerization catalytic activity (Ba + + < Li + < BrMg + <:: Na + < K + < < Cs+) is only slightly different . The concentration of the di a minoketone structures formed in the polymers of 8-octanelactam and 12-dodecanelactam under comparable reaction conditions is three to four times lower than in polycaprolactam. Condensation of diacylamine or acyllactam groups during the anionic polymerization of lactams gives rise to keto structures which are one of the causes of branching of macromolecules 1 • The extent of condensation is proportional to the initial concen­