1. Field of the Invention
The present invention relates to a process for producing a styrenic polymer and a catalyst for use therein. More particularly, it pertains to a process for efficiently producing a styrenic polymer having a high degree of syndiotactic configuration in the stereochemical structure of the polymer main chain and to a catalyst to be used in the process.
2. Description of the Related Arts
It has recently been disclosed by the research group of the present inventors that a styrenic polymer having a syndiotactic configuration is obtained by polymerizing a styrenic monomer by the use of a catalyst comprising as primary ingredients a transition-metal compound, especially a titanium compound and an alkylaluminoxane (Refer to Japanese Patent Application Laid-Open Nos. 187708/1987, 179906/1988, 241009/1988, etc.).
Methylaluminoxane, particularly suitable as an alkylaluminoxane is obtained usually by the reaction between trimethylaluminum and water. However, the above-mentioned reaction involves the problem that the reaction is difficult to put into practical production because of its violent reaction, and further suffers the disadvantages that in addition to requiring expensive trimethylaluminum as the starting material, an excessively large amount of methylaluminoxane is required as a component of the catalyst as compared with the amount of a transition metal, thus causing an extremely expensive catalyst, and further that a large amount of residual ash component remains in the product resin.
There has recently been reported that a polymerization catalyst not containing aluminoxane is capable of polymerizing .alpha.-olefin (principally, ethylene) by R. Taube (J. Organomet. Chem. C9-C11, 347 (1988)), H. Turner (J. Am. Chem. Soc. 111,2728 (1989)), R. F. Jordan (Organomet. 8,2892 (1989)), etc. As for styrenic monomer, there is disclosed in Japanese Patent Application Laid-Open No. 124706/1991, a process for producing a styrenic polymer free from aluminoxane by the use of an iron complex salt or an ammonium salt in place of alumioxane. Nevertheless the process still involves the problems that the use the iron complex salt causes coloring of the resultant resin due to the iron component as the residual ash in the resin, while the ammonium salt is not sufficient in catalytic activity.
Under such circumstances, intensive research and investigation were concentrated by the present inventors into the development of a catalyst capable of efficiently polymerizing a styrenic monomer into the styrenic polymer having a high degree of syndiotactic configuration with a least possible content of residual ash without the use of expensive aluminoxane required in a large amount and of the development of the process for producing the styrenic polymer by the use of the aforementioned catalyst.