A kinetic study of some carbonyl substitutions at the CONH group, with special reference to the mechanism of ϵ‐caprolactam polymerisation

Abstract

AbstractA kinetic study of some substitutions at the carbonyl group of simple N‐substituted amides has provided information on the mechanism of chemical interactions in polyamides generally, and in polymerizing caprolactam melts in particular.In polyamides the amide group may react in substitution either as the uncharged –CONH–, or as the amide conjugate acid –CONH+2–, giving uncatalyzed and acid‐catalyzed reactions respectively. Substituting groups may be the nucleophiles H2O, OH−, NH2, or COO−. Each of the resulting eight possible reactions has been discussed in turn, in the light of kinetic measurements in model systems. Some systematisation of these reactions has been made and the catalytic role of acid end‐groups clarified. There is agreement with other workers on the importance of acid‐catalyzed aminolysis in lactam systems, but it is possible that a different catalytic mechanism, not involving proton transfer to the amide, and not included in this investigation, may operate in certain circumstances.The need for an independent determination of the degree of ionisation of end‐groups in polyamides, as an aid to complete characterization of chemical interactions in such systems, is emphasized.