Isothermal anionic polymerization of ε‐caprolactam to polyamide‐6: kinetic modeling and application for production process

The in-situ anionic polymerization of ε-caprolactam (ε-CL) to polyamide-6 enables the production of large, near net shape fiber reinforced composites by thermoplastic resin transfer molding. For the propagation of the flow front as well as for the progress of the solidification, the simultaneous processes of polymerization and crystallization and the corresponding reaction kinetics play a central role. To investigate these processes, preparation of reactive mixtures consisting of ε-CL, activator, and initiator was carried out under inert atmosphere. A solvent-based activator and initiator were used, which hardly have been studied in the literature so far. In analogy to the resin transfer molding process, quasi-isothermal differential scanning calorimetry measurements were performed at various temperatures and the released enthalpy and the degree of crystallization were determined. From these isothermal measurements, a two-stage semi-empirical kinetic model was established for a solvent-based system for the first time, which reproduces the experimental data with high precision. To apply the obtained kinetic model to a thermoplastic resin transfer molding process it was finally correlated to dielectric sensor data, allowing real-time prediction of the total conversion