A method is provided to control the short chain branching (SCB) distribution of an ethylene-butene (EB) polyethylene resin that is prepared in a gas phase polymerization process using a specific type of magnesium-titanium Ziegler Natta catalyst. The method allows the level of short chain branching to be increased in the low molecular weight fraction of the resin by increasing the polymerization residence time. The polymers that are produced in accordance with this invention may be useful for the preparation of cast films and blown films, especially for stretch film applications.