Compounds of formula (I) are useful as addivitives in oleaginous compositions, wherein B represents an aromatic system, A represents a hydrocarbyl group, R1 and R2 are the same or are different and each independently is an aliphatic hydrocarbyl group containing 10-40 carbon atoms, provided that one of R1 and R2 may represent hydrogen; z is at least 1 and wherein the aromatic system carries at least one substituent group which is an activating group for the ring system or a derivative of an activating group.