Processes for producing impact copolymers are provided. Ethylene and at least one comonomer can be polymerized in the presence of one or more catalysts, polypropylene particles, and an inert solvent to produce an impact copolymer. The polypropylene particles can have a weight average particle size along the longest cross-sectional length thereof of about 0.05 mm to about 5 mm and a pore volume of less than 80%. The inert solvent can be present in a volume amount of about 0.1 to about 2 times the pore volume of the polypropylene particles.