The presence of different commonly used induced condensing agents (ICAs) in the gas phase polymerization of ethylene on the supported catalyst has a significant impact on the crystallinity and the molecular weight distribution of the resulting high density polyethylene. The crystallinity of the polymer is found to be higher in the presence of vaporized n-pentane or n-hexane, than in “dry mode” (i.e., with no ICA). This is primarily attributed to the mechanism of crystallization of polymer chains in presence of the solubilized ICA which might act to promote solvent vapor annealing. In addition, vaporized ICA also provokes a significant increase in the weight average molecular weight, with values being estimated at over one million. (Figure presented.) .