Olefin polymerization catalyst

A process for producing an olefin polymer comprising polymerizing an olefin with a catalyst system comprising

• (A) a solid titanium trichloride catalyst produced by the steps of
• (a) at a temperature of -40.degree. C. to 40.degree. C., over a period of 5 minutes to 6 hours, mixing titanium tetrachloride with from 0.2 to 1.1 moles per mole of said titanium tetrachloride of an organoaluminum compound of the formula (I):
• AlR.sub.n X.sub.3-n (I)
• wherein R has up to 10 carbon atoms and is an aliphatic hydrocarbon group which may be straight chain, branched chain or cyclic, or an aromatic hydrocarbon group;
• X is a halogen atom or a hydrogen atom;
• and n is a number satisfying the relation, 1.5.ltoreq.n.ltoreq.3;
• in the presence of from 0.1 to about 3 moles per mole of said titanium tetrachloride of an ether compound of the formula (II);
• R.sup.2 OR.sup.3 (II)
• wherein R.sup.2 and R.sup.3, which may be the same or different, each is an alkyl group, an aralkyl group or an alkenyl group, each having up to 10 carbon atoms, to reduce the titanium tetrachloride;
• (b) maintaining the mixed solution at a temperature of 10.degree. C. to 50.degree. C. for 1.5 to 6 hours thereby performing the reduction;
• (c) at the time when the reduction proceeds at least 90%, adding iodine in an amount of 0.01 to about 1 mole of said titanium tetrachloride to the resulting liquid titanium trichloride product;
• (d) maintaining the resulting mixture at about 30.degree. C. to about 150.degree. C. thereby precipitating solid titanium trichloride;
• and
• (e) then separating the solid titanium trichloride catalyst, and
• (B) an activating agent of the formula (III);
• AlR'.sub.m Y.sub.3-m (III)
• wherein R' has up to 10 carbon atoms and is an aliphatic hydrocarbon group which may be straight chain, branched chain or cyclic, or an aromatic hydrocarbon group;
• Y is a halogen atom or a hydrogen atom and m is a number satisfying the relation, 1.ltoreq.m.ltoreq.3.