Polyamides from lactams via anionic ring-opening polymerization: 2. Kinetics

Abstract

This paper summarizes a study of the kinetics of the anionic polymerization of caprolactam employing a bisimide (isophthaloyl-bis-caprolactam) as the initiator and caprolactam-magnesium-bromide as the catalyst. The early part of this investigation was devoted to the study of phenomenological polymerization kinetics via the adiabatic reactor method. Kinetic constants were determined by regression analysis using Malkin's autocatalytic model. The adiabatic temperature rise normally occurs in two stages. The first rise of about 50°C is due to the polymerization exotherm and is followed by a second, smaller temperature rise of about 10°C attributed to the polymer crystallization. (For the purpose of comparison, it should be noted that the typical adiabatic temperature rise of either polyester or vinyl-ester resin is about 150°C). The onset of crystallization is typically preceded by an induction period. The magnitude of temperature rise and the onset of crystallization (including the induction period) is dependent upon the initial polymerization temperature. In the 117–140°C temperature range, the correlation between the experimental and predicted polymerization and crystallization exotherms was excellent. At higher initial temperature (157°C), the polymerization exotherm was only 40°C and the crystallization exotherm was not observed.