Abstract: Provided is an olefin polymerization catalyst comprising the combination of:[I] a solid catalyst component comprising a solid material obtained by contacting the following components (1) to (4) and a titanium compound (5) supported on said solid material:(1) a magnesium halide,(2) a compound represented by the general formula ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are each a hydrocarbon radical having 1 to 24 carbon atoms, alkoxy, hydrogen, or halogen, R.sup.4 is a hydrocarbon radical having 1 to 24 carbon atoms and n is 1.ltoreq.n.ltoreq.30,(3) a compound represented by the general formula ##STR2## wherein R.sup.5 is hydrogen, halogen, or a hydrocarbon radical having 1 to 24 carbon atoms, R6 is a hydrocarbon radical having 1 to 24 carbon atoms, and r, p and q are integers selected from the following ranges: 1.ltoreq.r.ltoreq.3, 0.ltoreq.p<6, 0.ltoreq.q<6, provided 1.ltoreq.r+p+q<6, and(4) a compound represented by the general formula R.sup.7 -O-R.sup.8 wherein R.sup.7 and R.sup.

Abstract: Provided is a process for preparing a polyolefin, characterized by polymerizing at least one .alpha.-olefin in the presence of a catalyst which comprises the combination of:[I] a solid catalyst component comprising a solid substance obtained by contacting the following components (1) through (3) with one another and (4) a titanium compound supported on said solid substance:(1) a magnesium halide,(2) a compound represented by the general formula ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are each a hydrocarbon radical having 1 to 24 carbon atoms, an alkoxy group, hydrogen, or a halogen atom, R.sup.4 is a hydrocarbon radical having 1 to 24 carbon atoms and n is 1.ltoreq.n.ltoreq.30, and(3) at least one compound selected from the group consisting of:(a) compounds represented by the general formula ##STR2## wherein R is hydrogen, a halogen atom, or a hydrocarbon radical having 1 to 24 carbon atoms, and r, p and q are integers satisfying the following conditions:1.ltoreq.r.ltoreq.3, 0.ltoreq.p<6, 0.ltoreq.