Abstract: A process for purifying propylene homopolymers or copolymers which comprises:(i) polymerizing or copolymerizing propylene with other unsaturated hydrocarbon monomers in liquid propylene in the presence of a catalyst system consisting essentially of (a) an activated titanium trichloride obtained by reducing titanium tetrachloride with an organo-aluminum compound followed by activation and (b) an organo-aluminum compound;(ii) introducing the resulting polymer slurry into an upper portion of a counter-current washing tower to counter-currently contact the polymer slurry with a C.sub.3 -C.sub.8 alcohol and liquid propylene, whereby said catalyst is deactivated and at the same time the propylene homopolymers or copolymers dissolved in the polymer slurry and the catalyst are removed by washing, wherein said alcohol is used in an amount 0.

Abstract: In a process for producing a propylene homopolymer or copolymer which comprises polymerizing propylene or copolymerizing propylene and at least one other unsaturated hydrocarbon monomer in liquid propylene using a catalyst comprising activated titanium trichloride and an organo-aluminum compound, the activated titanium trichloride being prepared by reducing titanium tetrachloride with an organo-aluminum compound followed by activation, introducing the polymer slurry produced into the top of a counter-current washing tower, and washing the slurry by bringing the slurry into counter-current contact with liquid propylene which is introduced into the bottom of the washing tower, the improvement which comprises refining the homopolymer or copolymer of propylene by feeding (a) an alcohol having 3 to 8 carbon atoms in a molar amount of about 0.

Abstract: A process for producing a homopolymer of propylene or a copolymer of propylene which comprises polymerizing propylene or a mixture of propylene and another unsaturated hydrocarbon monomer such as ethylene in liquid propylene, in the presence of a catalyst system consisting essentially of (a) an activated titanium compound obtained by reducing titanium tetrachloride with an organic aluminum compound and activating the resulting titanium compound and (b) an organic aluminum compound to produce a polymer slurry, introducing the polymer slurry into an upper part of a counter-current washing zone, such as a washing tower, and counter-currently contacting the polymer slurry with liquid propylene which is introduced into a lower part of the washing zone, whereby the polymer and catalyst residues dissolved in the polymer slurry are removed.

Abstract: A process for polymerizing .alpha.-olefins in a solvent under conditions such that the polymer formed grows as particles, in which the process comprises reusing a greater part of the solvent used for the polymerization by recycling the solvent to the polymerization zone without carrying out any purification treatment.