Linear low density polyethylenes with high melt strength and high melt index ratio

Abstract

Linear low density polyethylenes (LLDPEs) that have relatively high melt index ratios (MIR) and relatively high melt strength (MS). This combination of melt properties is achieved by a substantially non blended LLDPE. Catalysts used to produce these polyethylenes are generally a blend of bridged bisindenyl zirconocene dichlorides, where one zirconocene contains saturated indenyls and the other unsaturated indenyls.

We claim:  
     
         1 . A mixed metallocene catalyst system, comprising: 
 a) a dimethylsilyl-bridged bis-indenyl zirconocene dichloride, wherein said indenyl is saturated; and    b) a dimethylsilyl-bridged bis indenyl zirconocene dichloride, wherein said indenyl is unsaturated.    
     
     
         2 . The mixed metallocene catalyst system of  claim 1  wherein said tetrahydroindenyl has a structure, represented by:  
       
         
           
           
               
               
           
         
         wherein said structure may have substituents or be unsubstituted.  
       
     
     
         3 . The mixed metallocene catalyst of  claim 2  wherein the substituents on the ring may be the same or different.  
     
     
         4 . The mixed metallocene catalyst of  claim 2  wherein the ring is unsubstituted.  
     
     
         5 . The mixed metallocene catalyst of  claim 1  wherein said system is supported.  
     
     
         6 . The mixed metallocene catalyst of  claim 5  wherein said support is one of silica, silicates, clay, alumina, composite oxides.  
     
     
         7 . The mixed metallocene catalyst of  claim 5  wherein said support is silica.  
     
     
         8 . The mixed catalyst of  claim 1  wherein said catalyst system is activated by one of methylalumoxane, modified methylalumoxane, non-coordinating anions, or mixtures thereof.  
     
     
         9 . The mixed catalyst of  claim 1  wherein said catalyst system is activated by methylalumoxane.  
     
     
         10 . The mixed catalyst system of  claim 1  wherein said saturated a) and said unsaturated) indenyl groups are present in said catalyst system at one of a ratio of 90:10, 10:90; 80:20, 20:80; 60:40, 40:60; or 50:50.  
     
     
         11 . The mixed catalyst system of  claim 1  wherein said a) is dimethylsilylbis(tetrahydro-1-indenyl) zirconium dichloride, b) is rac-dimethylsilylbis(1-indenyl)zirconium dichloride, and wherein said a) and said b) are present in said catalyst system in a ration of 60:40 to 40:60, and wherein said catalyst is activated by methyl alumoxane.  
     
     
         12 . A mixed catalyst system, comprising: 
 a) a bridged indenyl zirconocene dichloride wherein the indenyl group is saturated, and the substituents at each position are hydrogen; and    b) a bridged indenyl zirconocene dichloride, wherein the indenyl is unsaturated;    wherein said a) and said b) are each supported separately, on a silica support;    wherein said a) and b) are present in said catalyst system in a ratio of 40:60 to 60:40; and    c) wherein said catalyst system is activated by methylalumoxane.