Polyolefin production

Abstract

Use of a metallocene compound of general formula (IndH 4 ) 2 R″MQ 2 as a component of a catalyst system in producing polyethylene, wherein each Ind is the same or different and is indenyl or substituted indenyl; R″ is a bridge which comprises a C 1 to C 4 alkylene radical, a dialkyl germanium or silicon or siloxane, alkyl phosphine or amine, which bridge is substituted or unsubstituted, M is a Group IV metal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon atoms or halogen; and the ratio of meso to racemic forms of the metallocene in the catalyst system is at least 1:3. The metallocene may be supported. The ethylene may be polymerized in a reaction medium that is substantially free of any external comonomer, with comonomer being formed in situ. The produced polyethylene may have long chain branching. The produced polyethylene may be atactic.

1 . A process for preparing a polyethylene copolymer, which comprises: 
 polymerizing ethylene, without using an exogenous comonomer, with a catalyst system comprising:    a metallocene compound of general formula Ind 2 R″MQ 2  having a mole ratio of meso to racemic forms of the metallocene of at least 1:3, wherein 
 each Ind is the same or different, and is indenyl or substituted indenyl,  
 R″ is a bridge that is substituted or unsubstituted and comprises a C 1  to C 4  alkylene radical, a dialkyl germanium or silicon or siloxane, alkyl phosphine or amine,  
 M is a Group IV metal or vanadium,  
 each Q is a hydrocarbyl having 1 to 20 carbon atoms or a halogen,  
 said catalyst being further comprised of an inert support; and  
   wherein a cocatalyst is used to activate the metallocene compound.    
   
   
       2 . The process according to  claim 1 , wherein the polyethylene formed thereby has a shear ratio of at least 20.  
   
   
       3 . The process according to  claim 1 , wherein the cocatalyst comprises triisobutylaluminium (TBAC), and wherein said catalyst is precontacted with TBAC.  
   
   
       4 . The process according to  claim 1 , wherein hydrogen is added during polymerization.  
   
   
       5 . The process according to  claim 1 , wherein butane comonomer is formed in situ by dimerization of butane and wherein polymerization activity increases with increasing comonomer content.  
   
   
       6 . The process according to  claim 1 , wherein the polyethylene formed thereby has short chain branching arising from C 4  incorporation into the backbone of the polyethylene.  
   
   
       7 . The process according to  claim 1 , wherein the cyclopentadienyl ring of at least one of the indenyls is unsubstituted without regard to the bridge R″.  
   
   
       8 . A catalyst according to  claim 1 , wherein the cocatalyst comprises an aluminum-containing cocatalyst or a boron-containing cocatalyst.  
   
   
       9 . A catalyst according to  claim 1 , wherein the cocatalyst comprises an aluminum-containing cocatalyst comprised of an alumoxane, an alkyl aluminum and/or a Lewis acid.  
   
   
       10 . A long chain branched polyethylene copolymer formed by a process comprising: 
 copolymerizing ethylene in a reaction medium which comprises a solution or slurry with a catalyst system comprising:    a metallocene compound of general formula Ind 2 R″MQ 2  having a mole ratio of meso to racemic forms of the metallocene of at least 1:3, wherein 
 each Ind is the same or different and is indenyl or substituted indenyl,  
 R″ is a bridge that is substituted or unsubstituted and comprises a C 1  to C 4  alkylene radical, a dialkyl germanium or silicon or siloxane, alkyl phosphine or amine,  
 M is a Group IV metal or vanadium,  
 each Q is a hydrocarbyl having 1 to 20 carbon atoms or a halogen,  
 said catalyst being further comprised of an inert support;  
   using a cocatalyst which activates the metallocene compound; and    wherein said ethylene is polymerized without use of an exogenous comonomer.    
   
   
       11 . The process according to  claim 10 , wherein butane comonomer is formed in situ by dimerization of butane and wherein polymerization activity increases with increasing comonomer content.  
   
   
       12 . A catalyst according to  claim 10 , wherein R″ is an ethylene bridge.  
   
   
       13 . A catalyst according to  claim 10 , wherein both indenyls are unsubstituted without regard to the bridge R″.  
   
   
       14 . A catalyst according to  claim 10 , wherein M is Zr.  
   
   
       15 . A catalyst according to  claim 10 , wherein the Q is a halogen.  
   
   
       16 . A catalyst according to  claim 10 , wherein the bis indenyl compound is ethylene.  
   
   
       17 . A catalyst according to  claim 10 , wherein the cocatalyst which activates the metallocene compound comprises an aluminum-containing cocatalyst or a boron-containing cocatalyst.  
   
   
       18 . A catalyst according to  claim 10 , wherein the cocatalyst comprises an aluminum-containing cocatalyst comprising an alumoxane, an alkyl aluminum and/or a Lewis acid.  
   
   
       19 . A process for polymerizing ethylene comprising: 
 forming a supported metallocene catalyst by adding an alumoxane dissolved in an inert hydrocarbon solvent to a slurry of a inert particulate support, wherein said particulate support material comprises silica particles having a surface area within the range of 200-900 m 2 /g and a pore volume within the range of 0.5-4.0 ml/g;    adding a metallocene compound of the general formula Ind 2 R″MQ 2  having a mole ratio of meso to racemic forms of the metallocene of at least 1:3, wherein 
 each Ind is the same or different and is an indenyl or substituted indenyl,  
 R″ is a bridge that is substituted or unsubstituted and comprises a C 1  to C 4  alkylene radical, a dialkyl germanium or silicon or siloxane, alkyl phosphine or amine, M is a Group IV metal or vanadium,  
 each Q is hydrocarbyl having 1 to 20 carbon atoms or halogen;  
   contacting said supported catalyst with ethylene to polymerize ethylene to produce an ethylene copolymer; and    recovering said ethylene copolymer.    
   
   
       20 . The process of  claim 19 , wherein hydrogen is added to said reaction medium.  
   
   
       21 . The process of  claim 19 , wherein ethylene is polymerized in a reaction medium that is substantially free of any external comonomer.  
   
   
       22 . The process of  claim 19 , wherein atactic polyethylene is produced.