Abstract: Disclosed is a process for preparing a catalyst for polymerizing a mono olefin having 6 through 20 carbon atoms comprising mixing (a) a fatty acid having not less than 3 carbon atoms and (b) aluminum chloride, aluminum bromide or a mixture thereof in an amount of 0.7 through 1.2 mol of the component (b) based upon 1 mol of the component (a), to effect the condensation reaction of both components and a catalyst prepared by said process. This catalyst is suitable for use in the production of an olefin polymer having low viscosity and a high viscosity index.

Abstract: Disclosed is a process for preparing a catalyst for polymerizing a mono olefin having 6 through 20 carbon atoms comprising mixing (a) a fatty acid having not less than 3 carbon atoms and (b) aluminum chloride, aluminum bromide or a mixture thereof in an amount of 0.7 through 1.2 mol of the component .[.(b).]. .Iadd.(a) (i.e. aliphatic carboxylic acid) .Iaddend.based upon 1 mol of the component .[.(a).]. .Iadd.(b) (i.e. aluminum chloride, aluminum bromide or a mixture thereof), .Iaddend.to effect the condensation reaction of both components and a catalyst prepared by said process. This catalyst is suitable for use in the production of an olefin polymer having low viscosity and a high viscosity index.