A combination of nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry, matrix-assisted laser desorption/ionisation-collision induced dissociation (MALDI-CID) mass spectrometry and Fourier-transform infra-red (FTIR) spectroscopy has been employed for the characterisation of low molecular weight poly(methyl methacrylate) (PMMA) that was generated by means atom transfer radical polymerisation (ATRP). Evidence for the presence of a variety end group structures is shown. The terminating end groups included a five-membered lactone ring as well as the expected halogen (bromine or chlorine). Oligomers with other terminating end groups are proposed to be present at low abundance in the polymers. (c) 2005 Elsevier Ltd. All rights reserved.