The oligomeric products obtained by the polymerization of monomethacrylates of oligoethylene glycols possessing up to four oxyethylene units were examined by electrospray ionization mass spectrometry (ESI-MS). The oligomerization initiated by sodium and potassium hydrides proceeded via Michael-type addition of hydroxyl groups to carbon-carbon double bonds. Extended reaction time caused gelation, especially in the case of the more reactive potassium hydride. This study was focused on the structural assignments of the oligomeric products by use of ion trap multistage mass spectrometry (ESI-MS(2)). Precise structural characterization of the individual oligomers was based on fragmentation data.