A process for separating polymeric and gaseous components of a polymer-monomer mixture at a pressure of from 0.12 MPa to 0.6 MPa and a temperature of from 120° C. to 300° C. in a separation vessel is provided. The separation vessel has a vertically arranged cylindrical shape with a ratio of length to diameter L/D of from 0.6 to 10 and an inlet pipe capable of introducing the polymer-monomer mixture into the separation vessel which the inlet pipe extends vertically from the top of the separation vessel into the separation vessel. Further a process for preparing ethylene homopolymers or copolymers from ethylenically unsaturated monomers in the presence of free-radical polymerization initiators at temperatures from 100° C. to 350° C. and pressures in the range of from 110 MPa to 500 MPa comprising such a process for separating a polymer-monomer mixture is provided.