Anionic polymerization of caprolactam in organic media. Morphological aspects

Abstract

Crystalline entities formed during anionic polymerization of caprolactam (CL) in nonpolar solvents were examined, mainly by scanning electron microscopy and wide angle X-ray scattering. The morphological development of these entities is governed by the complex interaction between the competing polymerization and physical processes like phase separation and crystallization. The effect of the efficiency of catalytic systems on their interaction, the mechanisms of the phase separation and the crystal growth under topological restrictions set by the phase separation are discussed. Under reaction conditions, for these ones favouring high polymer yields, the final morphology of the polycaproamide (PCA) particles can be controlled by the efficiency of both catalytic species (activator and catalyst). Despite the large range of particle sizes two typical morphologies, namely – connected globules evolving to large blocks and macroporous powders are obtained using more or less efficient catalytic systems, respectively. An adequate selection of the catalytic pairs allows to control the particles’ size and their internal morphology, which is important for certain specific applications of PCA.