The invention provides a compound of the general formula: in which each X independently represents a polymer chain p represents an integer from 1 to 6 Y represents an amide group and Z represents either -CH.(CH2L)2 or -C(CH2L)(=CH2), in which each L independently represents a leaving group. The compounds are useful reagents for the conjugation of polymers to proteins, the resulting conjugates being novel and also forming part of the invention.
