Polypropylene polymerization process

Propylene polymers are made by copolymerizing at a temperature above 100 DEG C. a mixture of propylene and ethylene, in which the proportion of ethylene is 5 to 15% by volume of the propylene, in the presence of a catalyst comprising a titanium trichloride component and an aluminium alkyl component, e.g. triethyl aluminium. The preferred titanium trichloride component is obtained by reducing one mole of TiCl4 with about 1/3 of a mole of aluminium to give a material having the composition 3TiCl3: AlCl3. The polymerization is effected in a hydrocarbon diluent such as cyclohexane, and the polymer recovered by conventional techniques e.g. addition of isopropanol. After drying the polymer may be stabilized with a mixture of stabilizers including dilauryl thiodipropionate.