Preparation of polycondensate by one-step melt condensation in a vacuum

摘要

An improvement in the method of preparing a linear polycondensate of high molecular weight wherein a precondensate is initially formed and thereafter subjected to a one-step melt condensation in a vacuum while cleavage products are removed therefrom, the reaction mass being exposed in a thin layer by means of a stirrer to the reaction conditions, the improvement residing in employing as the precondensate a molten precondensate having an average condensation degree of at least 3, said precondensate being introduced into the melt condensation zone continuously while the cleavage products are driven off at the particular optimum, product-specific condensation temperature, the contents of the melt condensation zone being subjected to the action of a rotary stirrer until the melt has a melt viscosity of 1000 to 15000 poises and continuously withdrawing molten polycondensate in accordance with the speed of the reaction. Also disclosed is an apparatus in which the polycondensation is effected including an offset withdrawal outlet containing an auger which can enter a funnel disposed between the outlet and the polycondensation zone. Also disclosed is an upright multi-chamber vessel in which the precondensate is formed wherein the chambers are disposed one over the other. Some of the upper chambers are equipped with means for maintaining a normal or elevated pressure while some of the lower chambers are equipped with means for imposing a partial vacuum on the contents.