wherein R7 is a hydrogen atom or a lower alkyl group having 1 to 5 carbon atoms; R8 is a divalent hydrocarbon group having 1 to 30 carbon atoms which may contain a hetero atom; R9 is a monovalent hydrocarbon group having 1 to 30 carbon atoms which may contain a hetero atom; and p represents an average molar number of addition of R8O groups, and is a number from 1 to 60 and preferably a number from