Polycaprolactam melt of low monomer content - by treatment of melt in vacuum appts. (BE280776)

Method for prodn. of a polycaprolactam melt poor in monomer by direct spin process with the aid of a vacuum - tube, by treatment of the melt in an evacuation appts. sealed onto the vacuum tube at elevated temp. under vacuum and with branching off of a condensate which is recirculated to the vacuum tube, the polymer melt used contg. >9% monomer, the condensation temp. lying 95 degrees C, the melt to be evacuated having a temp. between 240 and 290 degrees C, evacuation taking place at a pressure between 6 and 60 Torr pre. between 10 and 20 Torr, and the condensate recirculated to the vacuum tube contg. monomer and cyclic dimer in ratio >150:1. Over an extremely long period, no blockage by cyclic dimer is observed. The use of monomer-rich melt has no influence of the props. of the evacuated prodt. The same chain distribution can be achieved as in the usual method which starts from the equilibrium polymerisate. Pref. the polymer melt contains 12-50% and the condensation temp. lies in the range 90-105 degrees C. A thin film evaporator is pref. used as the evacuation appts.