Ethylene polymer and processes for obtaining it

摘要

Ethylene polymer having a die swell ratio (RB) of at least 1.4, a resistance to crazing under stress (ESCR) of at least 55 h and a melt index (MI5) of at least 0.2 g/10 min. Processes for obtaining this ethylene polymer using different catalytic systems, the first based on titanium and zirconium used in a polymerization in two reactors; the second consisting of a mixture of a titanium catalyst and a titanium and zirconium catalyst, used in a polymerization in two reactors; the third based on chromium on a support comprising at least two constituents chosen from silica, alumina and aluminum phosphates, used in a polymerization in a single or in two reactors.