Synthesis of high molecular weight nylon 6 by anionic polymerization of epsilon-caprolactam. Mechanism and kinetics

Studies on the mechanism and kinetics of the anionic polymerization of epsilon-caprolactam were carried out by observing the kinetic data. The kinetic data were obtained as the functions of the concentrations of the catalyst and chain initiator. The rate equation of the polymerization was derived as follows, -d[M]/dt=k[I][C] ([C]less than or equal to 1.5x[I]) and -d[M]/dt=k'[I](2) ([C]>1.5x[I]). Here, [M], [I], and [C] are the concentrations of monomer, chain initiator, and catalyst, respectively. This suggests that the reaction between lactam-anion and polymer chain end (acyl-lactam) is the rate-determining step of the polymerization. The intermediate route of the rate-determining reaction is likely the pathway where the protonation occurs on the oxygen atom (at the initial stage of the reaction) and ring-opening follows. The values of apparent activation energy for the polymerization were 19.0 kcalmol(-1) ([C]less than or equal to 1.5x[I]) and 20.7 kcalmol(-1) ([C]>1.5x[I]), respectively.