Heterogeneous/homogeneous copolymer

Abstract

Novel polyethylene copolymer compositions prepared with a homogeneous catalyst system are characterized by having a unique high molecular weight, low comonomer (high density) fraction. These heterogeneous/homogeneous compositions may be prepared using a solution polymerization process in which the polymerization reactor contains a gradient in temperature, catalyst concentration or monomer concentration. The heterogeneous/homogeneous compositions of this invention are easily processed into films having excellent tear strengths and low hexane extractables.

1 . A heterogenized/homogeneous polymer composition comprising: 
 A) a first polymer fraction having a density of from 0.880 to 0.945 grams per cubic centimeter as measured by ASTM D792; a melt index, I 2 , of from 0.1 to 200 grams per 10 minutes as determined by ASTM D1238; less then 2 weight % hexane extractables; and a substantial absence of homopolymer wherein said first polymer fraction comprises at least one homogeneous copolymer of ethylene and at least one C 4to10  alpha olefin, and wherein each of said at least one homogeneous copolymer is characterized by having a molecular weight distribution, Mw/Mn, of less then three; and    B) a second polymer fraction having a higher molecular weight then said first fraction; a higher density then said first fraction; and a lower alpha olefin content then said first fraction, wherein said second polymer fraction comprises at least one second homogeneous polymer of ethylene, optionally with at least one C 4to10  alpha olefin comonomer, and wherein each of said at least one second homogeneous polymer of ethylene is characterized by having a molecular weight distribution, Mw/Mn, of less than 3.    
   
   
       2 . The polymer composition of  claim 1  when prepared in a solution polymerization process using a catalyst system comprising an organometallic complex of a group 4 metal having an activity greater than 250,000 grams of polymer composition per gram of said group 4 metal.  
   
   
       3 . The polymer composition of  claim 1  wherein said second polymer fraction contains less than 4 short chain branches per 1,000 carbon atoms.  
   
   
       4 . The polymer composition of  claim 1  containing from 80 to 99 weight % of said first polymer fraction and from 1 to 20 weight % of said second polymer fraction.  
   
   
       5 . The polymer composition of  claim 4  containing from 2 to 10 weight % of said second polymer fraction.  
   
   
       6 . The polymer composition of  claim 1  containing less than 2 weight % hexane extractables.  
   
   
       7 . The polymer composition of  claim 4  having an overall composition density of from 0.910 to 0.940 grams per cubic centimeter as determined by ASTM D792.  
   
   
       8 . The polymer composition of  claim 1  wherein said first polymer fraction comprises at least one homogeneous copolymer of ethylene and octene-1.  
   
   
       9 . Film prepared from the polymer composition of  claim 1 .  
   
   
       10 . Film prepared from a blend of the polymer composition of  claim 1  and at least one additional polyethylene selected from the group consisting of high pressure linear low density polyethylene; heterogeneous linear low density polyethylene; heterogeneous high density polyethylene; and homogeneous linear low density polyethylene.  
   
   
       11 . Film according to  claim 10  having a thickness of from 0.5 mil to 3.0 mil; a machine direction tear strength as determined by ASTM D1922 of greater than 300 grams per mil; and a hexane extractables content of less than 2 weight %.  
   
   
       12 . A multilayer film structure comprising at least one layer of film according to  claim 9 .  
   
   
       13 . A multilayer film structure comprising at least one layer of film according to  claim 10 .  
   
   
       14 . A sealed package manufactured from a film according to  claim 9 .  
   
   
       15 . A trash bag manufactured from a film according to  claim 9 .  
   
   
       16 . A liquid package manufactured from a film according to  claim 9 .  
   
   
       17 . A heavy-duty package manufactured from a film according to  claim 9 .  
   
   
       18 . A pallet wrap package manufactured from a film according to  claim 9.