heterofunctional polyethylene glycol or polyethylene oxide , represented by one of the following formula to : wherein : m is an integer from 5 to 10 , 000 ; n is an integer from 1 to 20 ; each r is independently an organic substituent , preferably an hydrocarbon substituent that preferably comprises at least one heteroatom , each a is independently an alkyl , a substituted alkyl group or an hydrogen atom , and the salts thereof . the above polymer architectures are produced by means of living anionic polymerization . since the polymerization procedure is a living process , it is possible to tailor the polymer molecular weight from oligomer containing few units of ethylene oxide to over 10 , 000 units of ethylene oxide units . these oligomers or polymers are expected to exhibit excellent biocompatibility , and are also expected to be utilized in the field such as carriers for drug delivery or diagnostic reagents .