stituted by C1 -C4 alkyl and/or an OH group, C7 -C8 phenylalkyl which is unsubstituted or mono-, di- or tri-substituted on the phenyl by C1 -C4 alkyl and/or an OH group, p is zero or an integer from 1 to 3, R6 and R9 are C1 -C18 alkyl, C5 -C8 cycloalkyl which is unsubstituted or mono-, di- or tri-substituted by C1 -C4 alkyl, C3 -C18 alkenyl or a group of the formula (III), R5 is a direct bond or C