On the relation between synthesis parameters and morphology of anionic polycaproamide obtained in organic media. I. Influence of the Na[O(CH2)2OCH3]2AlH2/ isophorone diisocyanate catalytic system

Polycaproamide granules were obtained by anionic polymerization of caprolactam in ethylbenzene, using the sodium bis(2-methoxyethoxy) aluminium hydride/isophorone diisocyanate catalytic system. Under these conditions, polymerization occurs heterogeneously and the nature of the particle growth seems to be essentially a microbulk one. The most suitable reaction conditions were established. The morphology of the granules was investigated by scanning electron microscopy. These granules result from the coalescence of a great number of small, spherical particles. the coalescence occurs during solidification of the separated polymer. Numerous globular formations were observed at the surface of the particles. The particles were individualized through mechanical dispersion and measured, and the average number of particles composing the aggregates was calculated. Using wide-angle X-ray scattering and differential scanning calormetry technics, the crystalline structure of the granular polycaproamide was studied. It contains almost entirely the α phase. The heat of fusion decreases slightly as compared with that corresponding to the anionic bulk polycaproamide. A schematic mechanism containing the stages involved in the obtaining of the granular polycaproamide is proposed.