Process for the manufacture of a composition comprising ethylene polymers

摘要

A composition of ethylene polymers comprising 30-70 wt.% of an ethylene homopolymer and an ethylene-hexene copolymer prepared in the presence of the homopolymer which consists of particles containing both polymers and is capable of being produced in a two reactor process. The homopolymer has a fluidity index MI2 (per ASTM D 1238 (1986) with load 2.16kg) 5-1000 g/10 min and relative density of at least 965 kg/m3. The copolymer has fluidity index MI5 (load 5kg) 0.1-2 g/10 min and relative density 910-940 kg/m3. The composition is prepared by suspension polymerization of ethylene in a first reactor in a medium comprising a diluent, hydrogen, a transition metal based catalyst and co-catalyst so as to form 30-70 wt.% of the final composition. The medium is removed from the first reactor, degassed of at least part of the hydrogen at reduced pressure and introduced to a second reactor together with ethylene, 1- hexene and, optionally, another alpha-olefin monomer. Suspension polymerization is then carried out to produce the ethylene-hexene copolymer forming the remaining 30-70 wt.% of the composition. An Independent claim is included for pipes obtained by extrusion of the composition.