. "y methyl and/or ethyl, or a radical of the formula ##STR11## and particularly methyl or C2-6 alkyl which is unsubstituted or substituted by C1-4 alkoxy or C3-6 alkoxyalkoxy, in particular alkyl havinng 1-6 C atoms and, in particular, 1-4 C atoms, and very particularly methyl or ethyl, m represents the number 1 or 2, preferably 1, and n and p independently of one another represent the number 1, 2 o" . . . .