It is known that polymers with improved stereoregularity can be obtained by using an organosilicon compound as a promoter of a Zieglar catalyst-on-carrier. Polyolefins having high stereoregularity can be a highly rigid material and are therefore of considerable utility. While a number of organosilicon compounds have been proposed to date as a promoter leading to high stereoregularity, some involve high production cost, some by-produce substances harmful to humans, and some attain only a low yield of polymers. Only a few organosilicon compounds are practically useful and exhibit satisfactory performance.
Compounds represented by formula (I) shown below are among the available organosilicon compounds that are practical and have satisfactory performance (as described in JP-A-5-287019, the term "JP-A" as used herein means an "unexamined published Japanese patent application"). However, it is received that low-molecular weight components contained in the resulting polyolefins in very small amounts reduce the rigidity of the polyolefins, and polyolefins having a further reduced content of low-molecular weight components have been demanded to meet the recent need of high rigidity materials.
Among the low-molecular weight components, boiling acetone-soluble components are considered particularly causative of the reduction in rigidity. Washing with an organic solvent is a well-known method for removing such low-molecular weight components. However, because washing is costly, it has been demanded to develop a method for removing low-molecular weight components without including a washing step.
Alkyltrialkoxysilanes are known as effective electron donors for Zieglar catalysts. Inter alia, thexyltrialkoxysilanes have extremely high industrial value because polyolefins having high stereoregularity can be obtained by using them as electron donor of a Zieglar catalyst on magnesium chloride, as disclosed in JP-A-5-287019.
Alkyltrichlorosilanes are known as not only raw material for silicone resins and surface treating agents for inorganic substances but also starting material for the above-mentioned alkyltrialkoxysilanes, and their importance has recently been increasing.
Processes for preparing alkyltrichlorosilanes, especially those having a branched alkyl group having 6 carbon atoms (e.g., a thexyl group) are disclosed, e.g., in Chem. Lett., p. 2247 (1987), J. Am. Chem. Soc., Vol. 70, p. 484 (1948), Chem. Listy., Vol. 52, p. 640 (1958), and Tetrahedron Lett., Vol. 26, p. 5511 (1985). These techniques provide alkyltrichlorosilanes either as a single substance or a mixture of structural isomers. In the former case, where a plurality of alkyltrichlorosilanes should be used in combination, other alkyltrichlorosilanes to be combined with an alkyltrichlorosilane obtained as a single substance must be prepared separately. In the latter case, it has been difficult to control the mixing ratio of the isomers being produced.