A process for preparing a catalyst component supported on a carrier, which comprises contacting in a treatment liquid (A) a titanium tetrahalide in the liquid or gaseous phase with (B) a solid in the absence of mechanical pulverization, at a temperature of 40.degree. C to the boiling point of the treatment liquid, to thereby chemically bond the titanium tetrahalide (A) to the solid (B), said solid (B) being obtained by either
- 1. mechanically pulverizing an adduct of a magnesium dihalide with a monocyclic aromatic monocarboxylic acid ester;
- 2. mechanically pulverizing a magnesium dihalide and an adduct of a magnesium dihalide with a monycyclic aromatic momocarboxylic acid ester;
- 3. mechanically pulverizing a monocyclic aromatic monocarboxylic acid ester and at least one magnesium dihalide component selected from the group consisting of magnesium dihalides and adducts thereof with monocyclic aromatic monocarboxylic acid esters;
- 4. mechanically pulverizing a magnesium dihalide and a complex of a titanium compound of the formula
- Ti(OR).sub.n X.sub.4-n
- wherein R is an alkyl radical, or a phenyl radical optionally substituted by a lower alkyl group, X is a halogen atom, and n is an integer of 0 to 4, with a monocyclic aromatic monocaroxylic acid ester;
- 5. mechanically pulverizing an adduct of a magnesium dihalide with a monocyclic aromatic monocarboxylic acid ester and at least one titanium component selected from the group consisting of titanium compounds of the formula
- Ti(OR).sub.n X.sub.4-n
- wherein R is an alkyl radical, or a phenyl radical optionally substituted by a lower alkyl group, X is a halogen atom, and n is an integer of 0 to 4, and complexes thereof with monocyclic aromatic monocarboxylic acid esters;
- 6. mechanically pulverizing a magnesium dihalide, an adduct of a magnesium dihalide with a monocyclic aromatic monocarboxylic acid ester, and at least one titanium component selected from the group consisting of titanium compounds of the formula
- Ti(OR).sub.n X.sub.4-n
- wherein R is an alkyl radical, or a phenyl radical optionally substituted by a lower alkyl group, X is a halogen atom, and n is an integer of 0 to 4, and complexes thereof with monocyclic aromatic monocarboxylic acid esters;
- or
- 7. mechanically pulverizing a monocyclic aromatic monocarboxylic acid ester, at least one magnesium dihalide component selected from the group consisting of magnesium dihalides and adducts thereof with monocyclic aromatic monocarboxylic acid esters, and at least one titanium component selected from the group consisting of titanium compounds of the formula
- Ti(OR).sub.n X.sub.4-n
- wherein R is an alkyl radical, or a phenyl radical optionally substituted by a lower alkyl group, X is a halogen atom, and n is an integer of 0 to 4, and complexes thereof with monocyclic aromatic monocarboxylic acid esters, wherein the amounts of the magnesium dihalide (a), the monocyclic aromatic monocarboxylic acid ester (b) and the titanium compound (c) of the above formula are selected such that the molar ratio of (a):(b) in (1), (2) and (3) above is 1:10 to 0.005 and the molar ratio of (a):(b):(c) in the case of (4), (5), (6) and (7) above is 1:
- (10 to 0.005):(100 to 0.001), and wherein when the adduct of magnesium dihalide or the complex of titanium compound is used, the amount of the monocyclic aromatic monocarboxylic acid ester therein is considered as the amount of (b) and wherein said monocyclic aromatic monocarboxylic acid ester (b) is an ester of benzoic acid, hydroxybenzoic acid, alkoxy benzoic acid or alkyl benzoic acid.