Polyethylene glycol carbamates

Compounds of the formula <IMAGE> (I) <IMAGE> in which R is alkyl having up to 4 carbon atoms, n has an average value of at least 9, X is a radical of the formula -C(=O)-(NH-SO2)m- in which m is 0 or 1 and, if m is 1, the carbonyl group may be bonded to the oxygen atom or to the nitrogen atom, and each of the radicals A1, A2 and A3, independently of the others, is hydrogen or an acyl radical, and salts of salt-forming compounds of formula I, as well as metal complexes of compounds of formula I, in which A1, A2 and A3 are hydrogen can be used as metal chelators and as auxiliaries in diagnosis.