Adjusting Polymer Composition

Abstract

A scavenger is used to indirectly control the ratio of polymer components in a polyethylene composition made using a combination catalyst comprising an inorganic chromium catalyst, and a group 4 single site catalyst.

1 - 25 . (canceled) 
     
     
         26 . A pipe manufactured from a polymer composition having a density of from 0.941 g/cc to 0.953 g/cc, the polymer composition being made by co-polymerizing ethylene and at least one co-monomer with a combination catalyst in the presence of a catalyst poison and a scavenger; wherein
 the combination catalyst comprises: an inorganic chromium catalyst, a group 4 single site catalyst, one or more activators, and a support;   the polymer composition comprises a first polymer component provided by the inorganic chromium catalyst and a second polymer component provided by the group 4 single site catalyst;   the catalyst poison reduces the polymerization activity of the group 4 single site catalyst relative to the inorganic chromium catalyst;   and the relative amounts of the first and second polymer components present in the polymer composition depend on the amount of scavenger present during co-polymerization in ppm (weight of the scavenger relative to the weight of the polymer composition produced in parts per million).   
     
     
         27 . The pipe of  claim 26  wherein the scavenger has the formula Al(R 1 ) n (R 2 ) 3-n ,
 where R 1  is a hydrocarbyl having from 1 to 20 carbon atoms; R 2  is independently selected from the group consisting of an alkoxide having from 1 to 20 carbon atoms, an aryloxide having from 6 to 20 carbon atoms, a halide, and a hydride; and n is a number from 1 to 3. 
 
     
     
         28 . The pipe of  claim 26  wherein the scavenger is supported. 
     
     
         29 . The pipe of  claim 26  wherein the scavenger is supported on an inorganic oxide. 
     
     
         30 . The pipe of  claim 26  wherein the scavenger is triethylaluminum. 
     
     
         31 . The pipe of  claim 26  wherein the group 4 single site catalyst has at least one phosphinimine ligand. 
     
     
         32 . The pipe of  claim 26  wherein the group 4 single site catalyst has the formula:
   L(PI)MX 2    
 where L is a cyclopentadienyl type ligand, PI is a phosphinimine ligand, M is Ti, Zr or Hf, and each X independently, is an activatable ligand. 
 
     
     
         33 . The pipe of  claim 26  wherein the inorganic chromium catalyst is a silyl chromate catalyst. 
     
     
         34 . The pipe of  claim 26  wherein the combination catalyst is a dual catalyst. 
     
     
         35 . The pipe of  claim 34  wherein the dual catalyst is supported on an inorganic oxide. 
     
     
         36 . The pipe of  claim 35 , wherein the dual catalyst system comprises:
 a) a silyl chromate catalyst; and   b) a group 4 single site catalyst having the formula:   
       
         
           
           
               
               
           
         
         
           wherein, M is a group 4 metal; PI is a phosphinimine ligand; L is a cyclopentadienyl type ligand; X is an activatable ligand; m is 1 or 2; n is 0 or 1; and p is an integer and the sum of m+n+p equals the valence state of M; and 
         
         c) one or more activators; 
         wherein, the molar ratio of Cr to group 4 metal in the dual catalyst is from 5:95 to 95:5. 
       
     
     
         37 . The pipe of  claim 26  wherein the first polymer component has a lower comonomer content than the second polymer component. 
     
     
         38 . The pipe of  claim 37  wherein the first polymer component has a lower weight average molecular weight than the second polymer component. 
     
     
         39 . The pipe of  claim 38  wherein the polymer composition has a molecular weight distribution which is bimodal when analyzed by gel permeation chromatography. 
     
     
         40 . The pipe of  claim 39  wherein the first polymer component represents from 95 to 25 wt % of the polymer composition and the second polymer component represents from 5 to 75 wt % of the polymer composition. 
     
     
         41 . The pipe of  claim 39  wherein the first polymer component represents from 99 to 80 wt % of the polymer composition and the second polymer component represents from 1 to 20 wt % of the polymer composition.