Polyethylene materials prepared using mixed ziegler-natta catalyst systems

Abstract

A polyethylene may be prepared using a mixture of a silica supported catalyst and a magnesium chloride supported catalyst. By changing the ratio of the two catalysts, the polyethylene produced may have a varying bulk density and shear response. The method allows for the tuning or targeting of properties to fit a specific application, such as a blow molding or vapor barrier film.

1 - 25 . (canceled) 
     
     
         26 . A process for preparing polyethylene comprising polymerizing ethylene monomer in the presence of a catalyst admixture, the catalyst admixture comprising a first silica supported Ziegler-Natta catalyst system and a second magnesium chloride supported Ziegler-Natta catalyst system wherein the molar ration of the first silica supported Ziegler-Natta catalyst system and the second magnesium chloride supported Ziegler-Natta catalyst system is from about 50:1 to about 1:50. 
     
     
         27 . The process of  claim 26  wherein the first silica supported catalyst and the second catalyst are admixed and introduced into a reactor. 
     
     
         28 . The process of  claim 26  wherein the first catalyst and the second catalyst are introduced sequentially to a reactor. 
     
     
         29 . The process of  claim 26  wherein the first catalyst and second catalyst are introduced into a reactor concurrently. 
     
     
         30 . The process of  claim 26  further comprising using an internal electron donor. 
     
     
         31 . The process of  claim 26  further comprising the use of an external electron donor. 
     
     
         32 . The process of  claim 26  further comprising the use of a solvent selected from the group consisting of toluene, heptane, hexane, octane, and mixtures thereof. 
     
     
         33 . The process of  claim 26  wherein the silica supported Ziegler-Natta catalyst system comprises a silica support having a surface area of from about 250 to about 500 m 2 /g; a pore volume of from about 1.1-2.5 mL/g; an average pore diameter of from about 170 to about 275 Å; and an average D 50  diameter of from about 10 to about 110 microns. 
     
     
         34 . The process of  claim 26  wherein the molar ratio of the first silica supported Ziegler-Natta catalyst system and the second magnesium chloride supported Ziegler-Natta catalyst system is from about 25:1 to about 1:25. 
     
     
         35 . The process of  claim 26  wherein the molar ratio of the first silica supported Ziegler-Natta catalyst system and the second magnesium chloride supported Ziegler-Natta catalyst system is about 1:1. 
     
     
         36 . The process of  claim 26  wherein the polyethylene is prepared in a loop reactor. 
     
     
         37 . The process of  claim 26  wherein the polyethylene is prepared in a stirred vessel reactor. 
     
     
         38 . The process of  claim 26  further comprising changing the rheological breadth of the polyethylene being prepared by changing the molar ratio of the first silica supported Ziegler-Natta catalyst system and the second magnesium chloride supported Ziegler-Natta catalyst system. 
     
     
         39 . The process of  claim 38  wherein the rheological breadth parameter, a, is decreased by increasing the amount of first silica supported Ziegler-Natta catalyst system. 
     
     
         40 . A polyethylene prepared by the method of  claim 26 . 
     
     
         41 . The polyethylene of  claim 40  wherein the polyethylene has a rheological breadth parameter of from about 0.11 to about 0.26. 
     
     
         42 . The polyethylene of  claim 40  wherein the polyethylene has a shear response of from about 9 to 18. 
     
     
         43 . The polyethylene of  claim 42  wherein the polyethylene has a shear response of from about 12 to 15. 
     
     
         44 . An article comprising a polyethylene of  claim 40 . 
     
     
         45 . The article of  claim 44  wherein the article is prepared using blown film extrusion, cast film extrusion, slit tape extrusion, rotomolding, blow molding, pipe extrusion, and foam sheet extrusion. 
     
     
         46 . The article of  claim 44  wherein the article is a film, fiber, pipe, textile material, feminine hygiene product, food packaging, grocery sack, or a pressure rated pipe.