ng a valence of u or an aryl group; R10 and R15 are a hydrogen atom, an alkyl group having 1-24 carbon atoms or an aryl group; R11, R12, R13 and R14 are a hydrogen atom, an alkyl group having 1-3 carbon atoms or an aryl group having 6-7 carbon atoms, in which said R9 -R15 may be the same or different, v is 0 or 1, and u is an integer of 1-4; and (3) a compound represented by the following general