products and serve to reduce the cost y 2 in the formula 1 represents the group linking the carboxyl group of fumaric acid to the silicon containing alkyl group in the formula the linear or branched c 3 10 alkylene includes propylene n butylene pentylene hexylene isopropylene and isobutylene in addition to these groups y 2 may be phenylene cyclohexylene u2014 ch 2 ch 2 o o u2014 ch 2 ch 2 ch 2 u2014 o is an integer from 1 to 10 or a group represented by any one of the following formulae since in general these groups are introduced simultaneously into fumaric acid by binding to the silicon containing alkyl group they are conveniently determined simultaneously with the selection of the silicon containing alkyl group typically y 2 is a propylene group which is easy to obtain x 1 x 2 and x 3 in the formula 1 are independently methyl trimethylsiloxy and organosiloxy groups with 18 si atoms or less such as pentamethyldisiloxy methylbis trimethylsiloxy siloxy tris pentamethylsiloxy siloxy trimethylsiloxydimethylsiloxy methylbis trimethylsiloxy siloxy mono methylbis trimethylsiloxy siloxy bis trimethylsiloxy siloxy tris methylbis trimethylsiloxy siloxy siloxy mono methylbis trimethylsiloxy siloxy bis trimethylsiloxy siloxy nonamethyltetrasiloxy pentadecamethylheptasiloxy heptacosamethyltridecasiloxy tris pentamethyldisiloxy siloxy nonamethyltetrasiloxyundecylmethylpentasiloxy and nonakis trimethylsiloxy tetrasiloxy the terminal hydrogen of the organosiloxy group may be replaced with alkyl group such as methyl ethyl butyl and amyl.