Adiabatic polymerization of ϵ‐caprolactam in presence of lithium chloride, 3. Oligomer formation

The activated anionic polymerization of ϵ‐caprolactam is strongly affected by LiCl addition to the polymerizing medium. Large variations in the yield of the polymerization products are induced by increasing salt content: both high polymer and cyclic dimer yields sharply decrease as functions of the salt concentration, whereas monomer and (in part) higher oligomers show a relevant increase. Also the production of low molecular weight side products is influenced by LiCl: higher salt concentrations induce the formation of larger amounts of side compounds. Monomer equilibrium data reveal that the salt negatively affects the thermodynamics of polymerization. ΔG variation as a function of LiCl content shows an increasingly relevant influence of the entropic contribution to the standard free energy change. The effects of LiCl on ring‐ring equilibria are qualitatively interpreted on the basis of both the strong ion‐ion interactions between Li+ ions and carbonyl groups and the interchain densification process.