Provided herein is a process of preparing a semi-random graft co-polymer, the product of which is difficult to fully characterize chemically. The product of the present disclosure has unique and useful properties of 1) binding to a peptide and 2) upon co-administration of the product and the peptide into animals the product prolongs the blood circulation time and elevates the level of the peptide, compared to the peptide alone without the product of the disclosure.