Process for producing propylene homopolymers and copolymers

A bulk polymerization process for producing a homopolymer or a copolymer of propylene, which comprises polymerizing propylene or a mixture of propylene and another unsaturated hydrocarbon monomer in liquid propylene in the presence of a catalyst system consisting essentially of (a) an activated titanium compound obtained by (1) reducing titanium tetrachloride with an organoaluminum compound represented by the formula

• R.sub.n AlX.sub.3-n (I)
• wherein R represents a straight or branched chain alkyl group having 1 to 18 carbon atoms, an alicylic hydrocarbon group or an aromatic hydrocarbon group, X represents a halogen atom, an n is a value of from 1 to 3, inclusive to obtain a .beta.-type titanium trichloride, (2) reacting the resulting .beta.-type titanium trichloride with an ether, (3) reacting the solid catalyst thus obtained with (i) an organoaluminum compound represented by the formula
• R'.sub.m AlX.sub.3-m (II)
• wherein R' represents a straight or branched chain alkyl group having 1 to 18 carbon atoms, an alicyclic hydrocarbon group or an aromatic hydrocarbon group, X represents a halogen atom, and m is a value of 0<m<1.5, followed by further reacting the resulting solid catalyst with an ether, or (ii) titanium tetrachloride and (b) an organoaluminum compound, withdrawing the obtained polymer slurry from the polymerization zone, introducing the polymer slurry into an upper part of a counter-current washing zone and counter-currently contacting the polymer slurry with liquid propylene introduced into a lower part of the washing zone, whereby the polymer and catalyst residue dissolved in the polymer slurry are removed.