A copolymer of ethylene and a higher alpha olefin, preferably 1-hexene, can
be produced using an activated chromium containing catalyst system and a
cocatalyst selected from the group consisting of trialkylboron,
trialkylsiloxyalutninum, and a combination of trialkylboron and
thalkylaluminum compounds. The polymerization process must be carefully
controlled to produce a copolymer resin having an exceptionally broad
molecular weight distribution, extremely high PENT ESCR values, and a
natural branch profile that impacts branching preferably into the high
molecular weight portion of the polymer. The resulting copolymer resin is
especially useful in high stiffness pipe applications.
