AbstractThe kinetics of crystallization during anioiiic polymerization of ϵ‐caprolactam was studied by the adiabatic temperature rise method, A new kinetic model for the non‐isothermal crystallization was derived and the possibility of its application was Investigated. By evaluating the parameters in the model for the given adiabatic system, the crystallization behavior during the; polymerization process was analyzed. The experimental and calculated temperature rise showed a very good agreement, which indicated that the model equation was appropriate to describe the non‐isothermal reaction‐induced crystallization kinetics in this study. The melting temperature of the reaction mixture increased steadily due to the change of the crystal structure with conversion. The equilibrium crystallinity was higher when the crystallization started in the presence of unreacted monomer than when the crystallization occurred after polymerization was completed. At lower conversion, the reaction mixture was less viscous, a condition that made transport to the liquid‐crystal interlace easier, and thus the activation energy for transport decreased. On the other hand, the increasing mobility resulted in difficulty in forming stable nuclei arid the free energy of nucleation