Patent ID: 6136924
Filing Date: 2000-10-24
Classification: C08F,C08L

Abstract:
A composition containing ethylene polymers comprising a polymer of high melt index and a polymer of low melt index prepared in at least two reactors, according to which ethylene, a catalyst derived from a transition metal selected from the group consisting of the elements of Group IIIB, IVB, VB and VIB of the periodic table and a cocatalyst are introduced into a first reactor; polymerization of the ethylene is carried out therein to produce a first ethylene polymer; a mixture comprising said first ethylene polymer, said introduced catalyst and said introduced cocatalyst is drawn off from said first reactor; wherein the mixture and ethylene are introduced into a second reactor, in which ethylene is polymerized to form a second ethylene polymer, the catalyst and cocatalyst being solely introduced into the first reactor, the weight ratio of the ethylene polymers being equal to (30 to 70):(70 to 30), and wherein the molecular weight distribution of a polymer produced in a single polymerization stage and under constant polymerization conditions in the presence of said catalyst is defined by a ratio M.sub.w /M.sub.n, between the weight-average molecular mass (M.sub.w) of the polymer and the number average molecular mass (M.sub.n) of the polymer, which is less than or equal to 10 and said catalyst further defined by a deactivation constant less than or equal to 0.5 h.sup.-1, and wherein the polymer of high melt index has a melt index MI.sub.2, measured under a load of 2.16 kg at 190.degree. C., of 5 to 1000 g/10 min and the polymer of low melt index has a melt index MI.sub.5, measured under a load of 5 kg at 190.degree. C., of 0.01 to 2 g/10 min, the ratio between these melt indices being from 500 to 50,000, the composition having a molecular weight distribution defined by a M.sub.w /M.sub.n, ratio of from 5 to 70, the composition further having a melt index MI.sub.5 of from 0.1 to 10 g/10 min and a dynamic viscosity .eta. expressed in dPa.s and measured at a rate gradient of 100 s.sup.-1 at 190.degree. C., corresponding to the relationship ##EQU2##