Propylene polymers of improved melt flow characteristics are obtained in a liquid pool propylene polymerization process carried out in the presence of a magnesium halide supported titanium halide-aluminum trialkyl catalyst system, where prior to its introduction to the polymerization reactor, the magnesium halide supported titanium halide catalyst component is admixed with an aromatic carboxylic acid ester electron donor and the mixture is subsequently introduced into the poymerization zone no later than about 5 days from the time of admixing.

A solid catalyst component for olefin polymerization in which the molar ratio of residual alkoxy groups to supported titanium is 0.60 or less is obtained by reacting the following compound (a1) with the following compound (b1) at a hydroxyl group/magnesium molar ratio of 1.0 or more, reacting the reaction mixture with the following compound (c1) at a halogen/magnesium molar ratio of 0.20 or more, reacting the resultant reaction mixture with the following compounds (d1) and (e) at a temperature of 120.degree. C. or higher but 150.degree. C. or lower, washing the reaction mixture with an inert solvent, reacting the reaction mixture with the following compound (e) again at the above temperature and washing the reaction mixture with an inert solvent, whereby there can be provided the solid catalyst component for olefin polymerization and a catalyst for olefin polymerization which have high polymerization activity and give an olefin polymer having a less residual Cl content and being excellent in stereoregularity and powder form and a process for producing an olefin polymer, (a1) an oxide of at least one element that is selected from Group II to Group IV elements and which supports an alcohol-free halogen-containing magnesium compound, (b1) an alcohol, (c1) a halogen-containing silicon compound, (d1) an electron-donating compound, and (e) a halogen-containing titanium compound.

A catalyst system useful for the polymerization of olefins which comprises (A) at least one organometallic compound of a typical metal belonging to I, II and III group of Periodic table, (B) a reaction production of (i) a solid organomagnesium compound of the formula: MgR.sub.l X.sub.2-1..alpha.D wherein R is a hydrocarbon group having 1 to 20 carbon atoms, X is a halogen atom, D is a Lewis base, l is a number in the range of 0<l<2 and .alpha. is a number in the range of 0.ltoreq..alpha.<1.5, (ii) a phenol compound, (iii) a Lewis base, and (iv) a titanium compound and/or vanadium compound, and optionally (C) a Lewis base in an amount of up to 1 mole to 1 mole of the component (A), and a process for homo- or copolymerization of olefins by using the catalyst system. The catalyst system of the present invention shows excellent activities not only per the transition metal compound but also per the solid catalyst and can give polyolefins having a high stereo-regularity.

In a process for producing an olefin polymer or copolymer by polymerizing an alpha-olefin having at least 3 carbon atoms or copolymerizing such alpha-olefins with each other or such an alpha-olefin with up to 20 mole % of ethylene and/or a diene in the presence of a catalyst comprising (1) a solid titanium catalyst component having magnesium, halogen, titanium, phosphorus and a carboxylic acid ester and (2) an organometallic compound of a metal of Groups I to III of the Mendelejeff's periodic table; the improvement wherein said catalyst is composed of (A) the solid titanium catalyst component (1) in which the molar ratio of the phosphorus to the carboxylic acid ester is from about 0.05 to about 2 and which has a specific surface area of not less than about 40 m.sup.2 /g, (B) the organometallic compound (2), and (C) an electron donor; and a catalyst used for aforesaid process.

A component for an olefin polymerisation catalyst which component is the product of treating a particulate support material with (a) an organomagnesium compound, (b) a transition metal compound of Groups IVA, VA or VIA, e.g. bis-butoxy titanium dichloride, (c) a pacifying agent, e.g. HCl and (d) optionally an aluminium compound, e.g. ethyl aluminium dichloride, an organometallic compound, e.g. zirconium tetrabenzyl, a halogenating agent e.g. silicon tetrachloride, or a Lewis Base compound, e.g. ethyl benzoate.