The collision-induced dissociation (CID) of PMMA oligomers cationized by various alkali ions (M⁺PMMAn) has been published [J.H. Scrivens, A.T. Jackson, H.T. Yates, M.R. Green, G. Critchley, J. Brown, R.H. Bateman, M.T. Bowers, J. Gidden, Int. J. Mass Spectrom. Ion Process. 1997, 165, 363]. The spectra mainly consist of two series of fragment peaks in the low m/z range (100-300) that have the metal cation still attached. These fragments appear to arise from the direct cleavage of each oligomer as shown below.

    The spectra also show that loss of metal cation becomes a competitive pathway as the size of the metal cation increases. For M⁺PMMA9, Li⁺ loss is negligible, Na⁺ loss is significant but not dominant, while loss of Rb⁺ and Cs⁺ completely dominate the CID spectra.
    To help explain these spectra, ion mobility experiments and molecular modeling were used to determine the preferred shapes of the M⁺PMMA oligomers and propose possible fragmentation mechanisms.