A graft macromer, comprising the reaction product of at least one macromer being at least one molecule which comprises in its structure one or more hydroxyl-terminated polyether and/or polyester chains, with at least one grafting compound which comprises in its structure at least one at least monoalkoxylated or at least monohalogenated silyl group and at least one alkyl, cycloalkyl or aryl containing group which is reactive towards the hydroxyl group of the macromer, is used for dispersing e.g. SiO2 in a polyol.