Anionic polymerization of ϵ-caprolactam in the presence of activators containing unsaturated groups

Abstract

Considerable interest is currently being shown in the anionic polymerization of ϵ-caprolactam (CL). This process is rapid and obviates the need for bulky equipment, while at the same time it may be used for the manufacture of poly-ϵ-caproamide (PCA) articles of practically any size and weight by means of the so-called “chemical moulding” process [1]. The anionic polymerization of lactams, particularly CL, proceeds readily in the presence of alkali metals such as sodium. The induction period of the reaction is considerably shortened by the addition of activators increasing the overall rate of the process [1,2]. The functional groups of the activator molecule responsible for this increase in the reaction rate may differ in structure, but Ney [2] and Vichterle [1] found that alkylimide compounds were the most effective. The structure of the activator has a marked effect on the structure and properties of the resulting polymer. In particular, a rise in the number of functional groups in the activator molecular leads to marked changes in the molecular and supermolecular structure of PCA [3], thus considerably influencing the mechanical behaviour of the polymers. Moreover, a characteristic dependence is observed between the mechanical properties and the number of functional groups in the activator molecule. For instance, if a monofunctional activator (e.g. N-acetyl-caprolactam) is replaced in the anionic polymerization of CL by a bifunctional one (e.g. N,N′-isophthaloyl-bis-caprolactam) the resulting polyamide (caprolite V) [4] will have better mechanical properties and higher molecular weight. The use of a trifunctional activator [5] in the anionic polymerization of CL results in the formation of branched PCA (caprolite P). As the functionality of the activators used in the anionic polymerization of CL increases there is a marked improvement in PCA strength, particularly in impact strength.