100 g of a straight-chain compound having a viscosity of 20,600 cSt at 25??? C. blocked with a methyldiacetoxysilyl group at both ends of the molecular chain, represented by the following formula: ##STR49## wherein Rf is a divalent group represented by the formula: ##STR50## wherein m and n are an integer such that m+n is 94 on average; 4.90 g of cyclohexanone (0.05 mol); 3.30 g of a carboxylic ac