Novel compounds of the general formula (I): in which X represents a polymer Q represents a linking group W represents an electron-withdrawing moiety or a moiety preparable by reduction of an electron-withdrawing moiety each of R1 and R2 independently represents a hydrogen atom or a C1-4alkyl group and either Z1 represents a protein or a peptide linked to CR2 via a nucleophilic moiety, and Z2 represents a molecule linked to CR2 via a nucleophilic moiety, or Z1 and Z2 together represent a single group derived from a protein or peptide linked to CR via two nucleophilic moieties.
