Patent ID: 7419600

Claim:
A method for preparing a purified polymer, said method comprising the steps of: providing an impure polymer composition comprising (i) a branched water-soluble polymer having the structure: where R is a non-reactive moiety, Z is a moiety comprising a site suitable for interacting with ion exchange chromatography media, PEG a and PEG b are each independently an end-capped polyethylene glycol (PEG), and P and Q each comprise a non-reactive linker absent an aromatic ring or ester group, and (ii) one or more polymeric impurities selected from the group consisting of PEG diol, end-canned PEG-OH, and activated end-capped PEG, and purifying said impure polymer composition by ion exchange chromatography under conditions effective to essentially remove said polymeric impurities and thereby provide said branched water-soluble polymer in essentially pure form.