Oligomerization of ethylene oxide during the functionalization of poly(butadienyl)lithium in benzene and cyclohexane at 25 degreesC has been investigated by MALDI-TOF MS and H-1 NMR. Chemically significant amounts of oligomer were found using 4 equiv. of ethylene oxide ([EO]/[PLi]) after 12 h in both benzene and cyclohexane. No oligomer was observed when the reaction time was minimized. (C) 2004 Elsevier Ltd. All rights reserved.