Abstract: A solid compound of a transition metal is ground in the presence of aluminium chloride, titanium tetrachloride and at least one organo-Lewis Base compound. The transition metal compound is typically titanium trichloride. The Lewis Base compound is an organo-phosphorus compound, preferably one which also contains nitrogen, such as 2-dimethylamino-1,3-dimethyl-1,3,2-diazaphospholidine-2-oxide or an organo-sulphur compound such as diphenyl sulphone. The solid compound of the transition metal may include aluminium chloride and if the amount of this aluminium chloride is at least 50% molar, there is no need to make a separate addition of aluminium chloride to the mixture which is ground. The ground product can be used as a component of an olefine polymerization catalyst.

Abstract: A titanium trihalide is ground with an organic Lewis Base compound which contains at least one phosphorus atom, and optionally at least one nitrogen atom, and a titanium tetrahalide, the Lewis Base and the titanium tetrahalide being used in amounts of 5 to 75, preferably 5 to 50%, molar and 1 to 50, preferably 5 to 30% molar respectively relative to the titanium trihalide. The materials are conveniently milled together and the milled product can be used as a component of an olefine polymerization catalyst and when such catalysts are used to polymerize propylene a high activity is achieved together with satisfactory stereospecificity.

Abstract: A polymerization catalyst comprises a solid transition metal compound which has been ground with a Lewis Base, an organo-metallic compound of a non-transition metal and a cyclic polyene, preferably with a further quantity of the same, or a different, Lewis Base. The catalyst can be used to polymerize propylene to give a high yield of a polymer having a flexural modulus in excess of 1.00 GN/m.sup.2.

Abstract: according to the present invention (1) a titanium trihalide is ground in the presence of from 5 up to 75% molar, relative to the titanium trihalide, of (2) a Lewis Base compound which is an organo-phosphorus compound of the formulaR.sub.1 R.sub.2 R.sub.3 P(O).sub.aand either (a) from 1 up to 50% molar, relative to the titanium trihalide, of a titanium tetrahalide and/or (b) from 0.2 up to 50% molar, relative to the titanium trihalide, of an oxidizing agent, wherein when a titanium tetrahalide is present, the molar quantity of the organo-phosphorus compound is at least equal to the molar quantity of the titanium tetrahalide.The titanium halides (1) and (a) are preferably the chlorides. Suitable forms of titanium trichloride are obtained by the reduction of titanium tetrachloride with hydrogen, titanium metal, aluminum metal or an organo-aluminium compound.