Process to produce polymers

Ethylene polymers produced by a process comprising polymerizing ethylene, or copolymerizing ethylene with at least one other monomer, wherein said polymerizing is conducted:

• in a loop reactor with isobutane as a diluent;
• at a temperature in a range of about 200° F. to about 220° F.;
• with a catalyst system comprising chromium and a support;
• in the presence of a trialkylboron;
• wherein the chromium is present in a range of about 1% by weight to about 4% by weight based on the weight of the support;
• wherein said support comprises silica and titania;
• wherein said support has a surface area of about 400 m2/gram to about 800 m2/gram and a pore volume of about 1.8 ml/gram to about 4 ml/gram;
• wherein the titania is present in an amount sufficient to give titanium in a range of about 0.5% by weight to about 3% by weight based on the weight of the support;
• wherein said catalyst system is activated at a temperature from about 1000° F. to about 1300° F.;
• wherein said trialkylboron is represented by the formula BR3, where R is an alkyl group of up to 12 carbon atoms;
• and
• wherein the process produces an ethylene polymer having the following properties:
• a high load melt index of 15 to 40 grams per ten minutes;
• a density of 0.952 to 0.958 grams per cubic centimeter, a shear ratio (high load melt index/melt index) of 120 to 200, a (weight average molecular weight/number average molecular weight) of 18 to 25, an Environmental Stress Crack Resistance (ASTM D1693, Condition A) of greater than 300 hours, less than 0.85% xylene solubles and less than 1.6% low molecular weight polymer.