100 g of a straight-chain compound having a viscosity of 18,700 cSt at 25??? C. blocked with a trimethoxysilyl group at both ends of the molecular chain, represented by the following formula: ##STR38## wherein Rf is a divalent group represented by the formula: ##STR39## wherein m and n are an integer such that m+n is 94 on average; 2.45 g of cyclohexanone (0.025 mol in terms of a carbonyl group);