Abstract: The present invention relates to novel key intermediates for the production of biologically active compounds coupled to polymers, of the general formula P--NCX.sub.2, wherein X designates a halogen atom selected from chlorine and bromine, and wherein P designates the polymer backbone of a polymer of the polyamide, polyester and ureaformaldehyde type. The invention further relates to compounds obtained by the reaction of the above compound P--NCX.sub.2 with a bifunctional or polyfunctional nucleophile. Suitable nucleophiles are hydrazides of dicarboxylic acids and amongst these there may be mentioned polyacrylamides partially substituted with acylhydrazide groups; polyfunctional amines selected from alkylamines, aralkylamines, arylamines and macromolecular compounds containing amino groups. The key intermediate PNCX.sub.2 may be coupled directly to biologically active macromolecules and amongst the preferred compounds of this type there are the various biologically active proteins and enzymes.