PURPOSE: To easily obtain the subject product for heat exchange, insulation and a lubricant by bringing a specific α-olefin monomer into contact with a catalyst containing boron trifluoride and alcohol alkoxylate to form an oligomer product.

CONSTITUTION: A 6-20C α-olefin monomer (e.g. 1-decene) is brought into contact with a catalyst containing boron trifluoride and alcohol alkoxylate (e.g. ethylene glycol monomethyl ether) to form an oligomer product and a co-dimer product composed of an oily compsn. containing an isomer mixture being a C16H32 isomer containing below 2.5 wt.% of a 7-methylpentadecene isomer in the case of a 1-octene dimer and a C20H40 isomer containing below 2.5 wt.% of a 9- methylnonadecene isomer in the case of a 1-decene dimer and a C18H36 isomer containing below 2.5 wt.% of a 7-methylheptadecene and/or a 9- methylheptadecene isomer in the case of a codimer.