N-vinylpyrrolidinone was polymerized in 3-methylbutan-2-one, which acted as both solvent and transfer agent. The main products of this reaction were poly(N-vinylpyrrolidinone)s with methyl ketone chain ends. These polymers were formed by transfer to solvent involving abstraction of hydrogen at either the isopropyl or 1-methyl position. MALDI-TOF mass spectrometry was used to fully characterize the polymers, and several other initiation and termination events were found to occur. Thus end groups associated with initiation by and combination with the primary radical were observed. Isopropyl end groups were formed as a result of fragmentation of 3-methylbutan-2-on-1-yl radical produced as a consequence of transfer to the 1-methyl group of 3-methylbutan-2-one. This fragmentation also yielded ketene, which underwent initial propagation followed by rapid extraction of a hydrogen atom from 3-methylbutan-2-one and yields aldehyde end groups, that were observed in both NMR and MALDI-TOF spectra. Also, end groups associated with termination by combination between propagating and solvent radicals were observed.