Patent ID: 6894126

Claim:
A process for preparing ethylene homopolymers and ethylene copolymers in a tube reactor by free-radical addition polymerization, in which first small amounts of free-radical chain initiator are supplied to a streaming flow medium comprising ethylene, molar mass regulator, and, if desired, polyethylene, after which the polymerization is then carried out, in which the polymerization is conducted at a pressure in the range from 2000 to 3500 bar and in which the reaction mixture within the tube reactor passes through a temperature profile in the range from 100 to 350° C., wherein the heat of reaction, liberated immediately, is taken off by water cooling, and wherein the water cooling is set up, for the preparation of ethylene homopolymer, in two zones, of which zone 1 encompasses the front two thirds of the total length of the tube reactor and of which zone 2 encompasses the last third of the total length of the tube reactor, the preferred water temperature for the cooling being calculated in accordance with the following formula: T(H 2 O) [° C.] zone 1=200−7.77·MFR and T(H 2 O) [° C.] zone 2=159−7.62·MFR, MFR denoting the melt index of the homopolymer obtained at the end of the reactor, in [dg/min], measured in accordance with ASTM D-1238, Condition (E).