Methods for controlling polymer properties

A method of producing a polyolefin comprising:

• contacting a reaction mixture and a reduced chromium oxide catalyst in a gas-phase reactor to produce the polyolefin, wherein the reaction mixture comprises ethylene and a co-monomer, and wherein the polyolefin is characterized by (i) a modified-Charpy impact strength of about 20 kJ/m2 or more and (ii) an equivalent stress cracking resistance of about 50 hours or more determined by notched constant ligament stress.

A composition comprising:

• a reduced chromium oxide-catalyzed polyolefin, wherein the reduced chromium oxide-catalyzed polyolefin is characterized by (i) a modified-Charpy impact strength of about 22 kJ/m2 or more and (ii) an equivalent stress cracking resistance of about 30 hours or more determined by notched constant ligament stress.

The composition of claim 30 wherein the modified-Charpy impact strength of the chromium-catalyzed polyolefin is about 22 kJ/m2 to 24 about kJ/m2.

The composition of claim 30 wherein the equivalent stress cracking resistance of the chromium-catalyzed polyolefin is about 60 hours or more.

A composition comprising:

• a chromium-catalyzed polyolefin, wherein the chromium-catalyzed polyolefin is characterized by (i) a modified-Charpy impact strength of about 20 kJ/m2 or more and (ii) an equivalent stress cracking resistance of about 50 hours or more determined by notched constant ligament stress.