Interpretation of Chain-Ring Equilibria in the Polymerization of Substituted ε-Caprolactam

If one of the hydrogens in ε‐caprolactam is substituted by a methyl or an ethyl group, the quantity of the lactam monomer remaining in its polymerization reaction is greater than that for the unsubstituted one. When the alkyl groups higher than ethyl are introduced, the lactam ring can hardly be polymerized. These shifts in chain‐ring equilibria are explained by the change in the thermodynamical properties caused by the existence of rotational isomers. The heat of reaction and the quantity of the remaining lactam ring at the equilibrium for $\alpha \mathrm{-}\mathrm{,\beta }\mathrm{-}\mathrm{,\gamma }\mathrm{-}\mathrm{,\delta }\mathrm{-}$ , and ε‐monomethyl and γ‐ethyl derivatives were estimated from this point of view. The calculated and the observed values are in good agreement.