Ethylene homopolymers and ethylene copolymers and a process for their preparation

摘要

Novel ethylene homopolymers and ethylene copolymers which are suitable for film production and have a density from 925 to 940 kg /m3, a melt flow index (MFI) of <1 g/10 min at 190 degrees C. and at an applied force of 2.16 kp can be prepared by free radical polymerization of the monomers at from 500 to 5000 bar and reaction temperatures T of from 40 degrees to 320 degrees C. by means of an initiator with virtually complete exclusion of oxygen in at least n=3 polymerization stages. In the first stage, the total amount or the predominant part of the monomers is subjected to the polymerization by means of part of the required initiator until the polymerization virtually comes to a stop. A further part of the initiator and, if required, of the monomers is then added to the mixture cooled to 20 degrees-60 degrees C. This process is repeated in the subsequent stages until the n th stage, at least the initiators used in the n th stage having a half-life temperature of from 90 degrees to 260 degrees C., and that the maximum reaction temperature Tmax being 270 degrees C. or higher, at least in the n th stage.