Novel compounds of the general formula:in which X represents a polymer,Q represents a linking groupW represents an electron-withdrawing moiety or a moiety preparable by reduction of an electron-withdrawing moietyeach of R1 and R2 independently represents a hydrogen atom or a C1-4alkyl group andeither 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 CR2 via two nucleophilic moieties.
