or linear or branched alkyl of 1 to 10 carbon atoms with the proviso that only one of R1, R2, R3, R4, R5 or R6 is --(CH2)m --O--(CH2)p --Z.sup.???.R'RR' or --O--(CH2)n --Z.sup.???.R'RR', and at least one of R1, R2, R3, R4, R5 or R6 is a halogen; and Z is N or P.