Polyethylene oxide (PEO) with 4-amino-N-(2-pyrimidinyl) benzene sulfonamide (APBS; PEOas) at one end was used as a carrier polymer for attachment (via the hydroxyl end group) of drugs such as mustard. For this purpose, the amine group of PEOas was protected first by the formation of a Schiff＇s base; then protected PEOas-Br and PEOas-NH2 were prepared. In order to attach N,N-dichloroethyl amine (DCEA) to the PEOas-NH2, DCEA hydrogen chloride salt was reacted with maleic anhydride first, then the resulting N,N-dichloroethyl maleinamic acid (DCEMA) could react with protected PEOas-NH2 continuously in the presence of dicyclohexylcarbodiimide (DCC). However, DCEMA is unstable; the chloroethyl group was rearranged to a corresponding ternary ammonium salt with a three-membered ring (DCEMA(r)). Therefore, the protected PEOas-NH2 was coupled with the DCEMA(r) in the presence of DCC; then it attacked the nucleophilic center of the aniline group of the APBS end of the PEOas after deprotection. Thus, a PEO with higher molecular weight and wider distribution was formed due to the intermolecular addition of PEOas.