A compound of the formula (I) according to claim 1, wherein R2 is C2 -C6 alkylene, n is 1, 2 or 3 and, if n is 1, A is a group of the formula (IIa)-(IIb) or (IId)-(IIe) in which X and Y which can be identical or different are C1 -C8 alkoxy or a group ##STR47## where R14 and R15 which can be identical or different are C1 -C12 alkyl, cyclohexyl, benzyl C2 -C3 alkyl substituted in the 2-position or 3