Abstract: An improved method of removing heat from polymerization reactions of normally gaseous monomers in the gas phase comprising feeding the monomer in liquid form to a polymerization zone, immediately after entering said zone, removing a portion of said gaseous monomer from the polymerization zone, liquefying said portion of monomer by cooling it at the same pressure as that prevailing in the polymerization zone, recycling the liquefied monomer to the polymerization zone together with fresh monomer in liquid form and causing said liquid monomer to change to the gaseous form immediately after entering said zone. The improvement consists in not only condensing the monomer outside the polymerization zone but also storing the same, in keeping the temperature in the polymerization zone constant by regulating the rate at which liquid monomer is fed to the zone, and in keeping the temperature and pressure in the polymerization zone within limits conducive to the gaseous state of the monomer.