Method for producing polyolefin

In a method for producing a solid catalyst carrier having a surface hydroxyl group concentration of up to 3 .mu. mole/m.sup.2 which is useful for preparing a catalyst containing (A) a solid catalyst component, (B) an organoaluminum compound and (C) an electron donating compound;

• which catalyst is useful for polymerizing an .alpha.-olefin having three or more carbon atoms for copolymerizing an .alpha.-olefin having three or more carbon atoms and ethylene;
• the improvement comprising:
• contacting at least one member selected from the group consisting of oxides of elements belonging to Groups II, III and IV of the periodic table and a composite of inorganic oxides containing at least one such oxide, with at least one silicon halide selected from the group consisting of alkylchlorosilanes having 1-6 carbon atoms and tetrachlorosilane, in a molar ratio of 1-50:1 with respect to said oxides;
• contacting the product thereof with an aliphatic monovalent alcohol in a ratio of 1-100:1 with respect to said silicon halide;
• separating the resulting solid after said contacting;
• contacting the resulting solid with a solution containing a magnesium alkoxide represented by the formula:
• Mg(OR.sup.2).sub.t (OR.sup.3).sub.2-5
• wherein R.sup.2 and R.sup.3 are the same or different, and each represents an alkyl group of 1-10 carbon atoms, and t is a real number of 0 to 2, wherein said solution containing a magnesium alkoxide is a mixture thereof with at least one additional member selected from the group consisting of a hydrocarbon, an electron donor and an alkoxytitanium compound;
• and
• contacting the product thereof with tetrachlorosilane.