Abstract: A Ziegler-Natta procatalyst composition in the form of solid particles and comprising magnesium, halide and transition metal moieties, said particles having an average size (D50) of from 10 to 70 ?m, characterized in that at least 5 percent of the particles have internal void volume substantially or fully enclosed by a monolithic surface layer (shell), said layer being characterized by an average shell thickness/particle size ratio (Thickness Ratio) determined by SEM techniques for particles having particle size greater than 30 ?m of greater than 0.2.

Abstract: A gas phase polymerization process comprising: (1) preparing a solution of a catalyst precursor comprising a mixture of magnesium and titanium compounds, an electron donor and a solvent; (2) adding a filler to the solution from step (1) to form a slurry; (3) spray drying the slurry from step (2) at a temperature of 100 to 140° C. to form a spray dried precursor, (4) slurring the spray dried precursor from step (3) in mineral oil, (5) partially or fully pre-activating the catalyst precursor by contacting the slurry of (4) with one or more Lewis Acids, and (6) transferring the partially or fully activated precursor from step (5) into a gas phase reactor in which an olefin polymerization reaction is in progress.