A process for producing a polymer or copolymer of an olefin containing at least 3 carbon atoms which comprises polymerizing or copolymerizing at least one olefin containing at least 3 carbon atoms, or copolymerizing the olefin with up to 10 mole% of ethylene and/or a diolefin, in the presence of a catalyst composed of (A) a magnesium-containing solid titanium composition and (B) an organo-aluminum compound;
- characterized in that the solid titanium composition (A) is a composition consisting essentially of the product formed by contacting (i) a halogen-containing magnesium organo-aromatic compound of the formula Mg(OR)Cl wherein R represents a radical selected from the group consisting of phenyl, naphthyl, lower alkyl-substituted phenyl, lower alkyl-substituted naphthyl, lower alkoxy-substituted phenyl, lower alkoxy-substituted naphthyl, halogen-substituted phenyl, halogen-substituted naphthyl, phenyl lower alkyl, lower alkyl-substituted phenyl lower alkyl, lower alkoxy-substituted phenyl lower alkyl and halogen-substituted phenyl lower alkyl, with (ii) an organic acid ester at a temperature of about 0.degree. to 200.degree. C. in the absence of mechanical pulverization, and further contacting the resultant product with (iii) a tetravalent titanium compound of the formula Ti(OR').sub.g X.sub.4-g wherein R' is an alkyl group containing 1 to 8 carbon atoms, X is a halogen atom and g is 0 to 4, at room temperature to 130.degree. C. in the absence of mechanical pulverization, so as to form the solid titanium composition in which the amounts of titanium, magnesium, halogen and organic acid ester are respectively 1-5% by weight, 10-25% by weight, 40-65% by weight and 5-20% by weight, said organic acid ester (ii) being a member selected from the group consisting of
- (a) esters formed between carboxylic acids or halogensubstituted derivatives selected from saturated or unsaturated aliphatic carboxylic acids containing 1 to 18 carbon atoms and halogen-substituted derivatives thereof and alcohols or phenols selected from saturated or unsaturated aliphatic primary alcohols containing 1 to 18 carbon atoms, saturated or unsaturated alicyclic alcohols containing 3 to 8 carbon atoms, phenols containing 6 to 10 carbon atoms and C.sub.1 -C.sub.4 saturated or unsaturated aliphatic primary alcohols bonded to the ring carbon atom of a C.sub.3 -C.sub.10 aliphatic or aromatic ring,
- (b) aliphatic lactones containing 3 to 10 carbon atoms,
- (c) an ester formed between an alicyclic carboxylic acid containing 6 to 12 carbon atoms and a saturated aliphatic primary alcohol containing 1 to 8 carbon atoms,
- (d) esters formed between aromatic carboxylic acids containing 7 to 18 carbon atoms and alcohols or phenols selected from saturated or unsaturated aliphatic primary alcohols containing 1 to 18 carbon atoms, saturated or unsaturated alicyclic alcohols containing 3 to 8 carbon atoms, phenols containing 6 to 10 carbon atoms and C.sub.1 -C.sub.4 saturated or unsaturated aliphatic primary alcohols bonded to the ring carbon atoms of a C.sub.3 -C.sub.10 aliphatic or aromatic ring, and
- (e) aromatic lactones containing 8 to 12 carbon atoms and the organo-aluminum compound (B) is selected from the group consisting of trialkyl aluminum, alkenyl aluminum, alkyl aluminum alkoxide, alkyl aluminum hydride and alkyl aluminum halide.