Patent Application

App. No. 12/156,844

Abstract

Claims (20)

1 . A process for making a bimodal polyethylene resin comprising:

(a) polymerizing ethylene in the absence or substantial absence of comonomer in a first reactor in the presence of a high activity solid transition metal-containing catalyst, organoaluminum cocatalyst, hydrogen and alkoxysilane to produce a polymerizate containing a first polymer;

(b) removing substantially all hydrogen from the polymerizate and transferring to a second reactor; and

(c) adding ethylene, a C 4-8 α-olefin comonomer and hydrogen to the second reactor and continuing the polymerization to produce a bimodal polyethylene product comprised of said first polymer and a second polymer of relatively lower density and higher molecular weight than that of the first polymer.

2 . The process of claim 1 wherein the weight ratio of first polymer to second polymer is from 65:35 to 40:60.

3 . The process of claim 1 wherein the alkoxysilane has the formula R* 4-y Si (OR*) y where y is 2 or 3 and R* is independently an alkyl or cycloalkyl group.

4 . The process of claim 3 wherein the alkoxysilane is selected from the group consisting of cyclohexylmethyldimethoxysilane and methyltriethoxysilane and mixtures thereof.

5 . The process of claim 1 wherein the α-olefin comonomer is selected from the group consisting of butene-1, hexene-1 and octene-1 and mixtures thereof.

6 . The process of claim 1 wherein the polymerizations are carried out in an inert hydrocarbon.

7 . The process of claim 1 wherein the alkoxysilane is cyclohexylmethyldimethoxysilane and the α-olefin comonomer is butene-1.

8 . The process of claim 2 wherein the weight ratio of first polymer to second polymer is from 60:40 to 45:55.

9 . The process of claim 2 wherein conditions in the first reactor are maintained to target the formation of first polymer having a density of 0.964 g/cm 3 or above and MI 2 in the range 50 to 400 g/10 min and conditions in the second reactor are maintained to target a final bimodal product density of 0.946 to 0.955 g/cm 3 and final bimodal product HLMI of 3 to 16 g/10 min.

10 . The process of claim 9 wherein the polymerizations are carried out in an inert hydrocarbon, the alkoxysilane is cyclohexylmethyldimethoxysilane and the α-olefin comonomer is butene-1.

11 . A bimodal polyethylene resin comprised of a first low molecular weight high density polyethylene component and a second higher molecular weight lower density polyethylene component produced by the process of claim 1 , said resin having a density of 0.945 to 0.956 g/cm 3 , HLMI of 2 to 20 g/10 min and trefBR index of 0.001 to 0.5.

12 . The bimodal polyethylene resin of claim 11 wherein the weight ratio of first polyethylene component to second polyethylene component is from 60:40 to 45:55.

13 . The bimodal polyethylene resin of claim 11 wherein the first polyethylene component has a density of 0.964 to 0.975 g/cm 3 and MI 2 of 100 to 300 g/10 min.

14 . The bimodal polyethylene resin of claim 13 having a density of 0.947 to 0.954, HLMI from 4 to 14 g/10 min and trefBR index from 0.01 to 0.2.

15 . The bimodal resin of claim 14 wherein the second polyethylene component is a copolymer of ethylene and butene-1.

16 . A bimodal polyethylene resin produced by the process of claim 10 comprised of a first low molecular weight high density polyethylene component having a density of 0.966 to 0.975 g/cm 3 and MI 2 of 150 to 250 g/10 min and a second higher molecular weight lower density ethylene-butene-1 copolymer component, said bimodal polyethylene resin having a density from 0.947 to 0.954 g/cm 3 , HLMI from 4 to 14 g/10 min and trefBR index from 0.01 to 0.2.

17 . Extruded pipe comprising the resin of claim 11 .

Assignments (14)