A pharmaceutically-active polymeric compound of the general formula (I),Y-[Yn-LINK B-X]m-LINK B (I)wherein (i) X is a coupled biological coupling agent of the general formula (II)Bio-LINK A-Bio (II)wherein Bio is a biologically active agent fragment or precursor thereof linked to LINK A through a hydrolysable covalent bond and LINK A is a coupled central flexible linear first segment of <2000 theoretical molecular weight linked to each of said Bio fragments(ii) Y is LINK B-OLIGO wherein(a) LINK B is a coupled second segment linking one OLIGO to another OLIGO and an OLIGO to X or precursor thereof and(b) OLIGO is a short length of polymer segment having a molecular weight of less than 5,000 and comprising less than 100 monomeric repeating units(iii) m is 1-40 and(iv) n is selected from 2-50. The compounds are useful as biomaterials, particularly, providing antibacterial activity in vivo. Also provided are biological coupling agents useful as intermediates in the preparation of the pharmaceutically-active polymeric compounds.