The invention relates to a catalyst system for polymerization of propylene, the catalyst system comprising a Ziegler Natta procatalyst, an organoaluminium cocatalyst, a monoester of an aromatic carboxylic acid as the internal donor and ethyl-4-isopropoxy benzoate as the selectivity control agent. The invention also relates to a process for polymerization using the catalyst system as well as to polymers prepared by the process.
