Process for preparing poly (ethylene glycol) and modified protein.

ETHYLENE GLYCOL DERIVATIVES OF HIGH PURITY of formula (I) are used as MODIFYING PROTEIN interferons, tPA, EGF, various hormones, ETC. PROTEIN MODIFIED THUS having antigenicity minimized, LONG LIFE FOR SEMI-PLASMA OR TRANSFER ENHANCED TISSUE. ALSO DISCOVERED A NEW FOR PREPARING POLYETHYLENE GLYCOL DERIVATIVE HIGH PURITY PROCESS.