Propylene preliminary polymerization

A process for propylene bulk preliminary polymerization, comprising:

• feeding propylene monomer and a Ziegler-Natta catalyst system comprising (a) a pro-catalyst having an internal electron donor comprising a substituted phenylene aromatic diester and (b) a catalyst activator, into a continuous stirred-tank preliminary polymerization reactor that comprises a feeding apparatus connected thereto, configured to feed propylene monomer and the Ziegler-Natta catalyst system into the continuous stirred-tank preliminary polymerization reactor,
• wherein the feeding apparatus is configured to carry out said feeding without pre-contact of the pro-catalyst with the catalyst activator, and also without pre-contact of the catalyst activator with the propylene monomer before entering the continuous stirred-tank preliminary polymerization reactor,
• wherein the propylene monomer and the Ziegler-Natta catalyst system, when in the continuous stirred-tank preliminary polymerization reactor, are in a liquid medium that is passed through the continuous stirred-tank preliminary polymerization reactor, and
• wherein the process is carried out in the absence of, and the liquid medium does not have, saturated hydrocarbon diluent.