Abstract: Poly-carbonyloxyurethanes of the formula:A O--CO--NH--O--CO--R!.sub.n (1)wherein A is a linking group to which the oxygen atoms are attached at alkyl, cycloalkyl or aryl carbon atoms, n is an integer of value at least 2, and each R which may be the same or different, is the residue of a monobasic carboxylic acid of formula R--COOH, and their salts, especially salts with cations based on teritary amines, are useful cross-linking or chain-extending agents for natural or synthetic polymers, or may be used as adhesives for binding these materials to each other or to metal substrates.