US Patent 7714088 Poly(ethylene glycol) derivatives with proximal reactive groups

An activated, substantially water-soluble poly(ethylene glycol) is provided having of a linear or branched poly(ethylene glycol) backbone and at least one terminus linked to the backbone through a hydrolytically stable linkage, wherein the terminus is branched and has proximal reactive groups. The free reactive groups are capable of reacting with active moieties in a biologically active agent such as a protein or peptide thus forming conjugates between the activated (polyethylene glycol) and the biologically active agent.