ched alkyl group having 1-10 carbon atoms, linear or branched alkoxyl group having 1-10 carbon atoms, or linear or branched alkoxycarbonyl group having 2-11 carbon atoms, R7 indicates a hydrogen atom or a linear or branched alkyl group having 1-10 carbon atoms, two or more R7 groups, if present, being either the same or different, p is an integer of 0-3, R8 individually represents a linear or bran