Method of polymerizing 1-olefins

A method of making polymers of one or more 1-olefins which comprises polymerizing said olefins under polymerizing conditions with a catalyst active in the presence of an alkyl aluminum co-catalyst, said catalyst being prepared by mixing, in the presence of a solvent, reactive materials comprising dry particles of silica, said particles having been preactivated by heating at between about 200.degree. C. and 900.degree. C., and a complex of the general formula (MgR.sub.2).sub.m (AlR.sub.3 ').sub.n where R and R' are alkyl groups and m/n is between about 0.5 and 10, inclusive, to form a reaction mixture of said solvent and a hydrocarbon insoluble first reaction product, and mixing said reaction mixture with a halide, oxyhalide or alkoxyhalide of tetravalent titanium to form a second reaction product, and evaporating said solvent from said second reaction product, said titanium compound being present in substantially equimolar ratio with respect to said active hydroxyl and oxide groups in said silica and with respect to the total magnesium and aluminum present in said first reaction product.