Patent ID: 6018006
Filing Date: 2000-01-25
Classification: C08F

Abstract:
A process for polymerizing ethylene at low pressure comprising(A) preparing a polymerization catalyst in the following stages:(a) milling analytical grade magnesium chloride in a ball mill with 10% by weight of ethyl benzoate in an inert atmosphere, at room temperature, for about 48 hours, up to suppression of the 2.56 A peak in the X-ray spectrum;(b) calcining at 600-800.degree. C., alumina of about 200-500 m.sup.2 /g of surface area and pore volume between 1.3 and 3.5 cm.sup.3 /g, for 4-8 hours;(c) mixing thoroughly the activated alumina of b) at rates ranging from 15 to 85% by weight, of the MgCl.sub.2 prepared in a), the mixing being done in a ball mill at room temperature, for at least two hours, in an inert atmosphere;(d) impregnating the support prepared in c) with 5 to 7.5 times by weight of titanium tetrachloride in an inert atmosphere and stirring for two hours at 80.degree. C., so as to deposit from 1.3 to 2.0% by weight of titanium; and(e) washing the surplus TiCl.sub.4 off with n-hexane at 50.degree. C.; and(B) contacting the impregnated and washed support with ethylene to be polymerized, to provide a polyethylene which comprises (i) high molecular weight chains having MW.gtoreq.10.sup.6 in an amount of 3.5 to 6.5 wt % of the total polyethylene, and (ii) lower molecular weight chains having MW.gtoreq.10.sup.5 in an amount of 35 to 55 wt % of the total polyethylene, wherein the melt flow index of the polyethylene is from 0.32 to 0.10 g/10 min.