PURPOSE: To obtain the subject compound useful as a synthetic reaction reagent, etc., on an industrial scale at a low cost by reacting 1,1,3,3-tetramethyldisiloxane with a methacrylate in the presence of a specific catalyst and a molecular sieve.

CONSTITUTION: The objective compound of formula II, e.g. 5,5,7,7-tetramethyl-3,9- bis (1-methylethylidene)-2,4,6,8,10-pentaoxa-5,7-disilaundecane, can be produced by adding a molecular sieve or a synthetic zeolite together with RhCl3.3H2O as a catalyst to 1,1,3,3-tetramethyldisiloxane, stirring the mixture preferably at 30-45°C for 0.5-1hr, cooling to room temperature, adding a compound of formula I [R is (silyl-terminated) alkyl or aryl] and reacting preferably at 15-65°C for 1-3hr. Preferably, the amounts of the compound of formula I, the catalyst and the molecular sieve, etc., are 2.1-2.5 times mol, 0.01-0.1mol% and 5-15wt.% based on the disiloxane, respectively.