Structural characterization of poly(N-alkyl-4-vinylpyridinium) triflates using pyrolysis/tandem mass spectrometry

Desorption chemical ionization (DCI) and desorption electron ionization (DEI) of homo- and co-polymers of N-alkyl-4-vinylpyridinium triflates having ethyl, n-hexyl and n-dodecyl groups as N-alkyl substituents, produce mass spectra that display oligomeric ions. These positively charged ions are singly-charged and result from cleavage of the polymer into neutral oligomers and the loss of a single triflate anion per oligomer. Analogous negatively charged ions, in which each neutral oligomer carries an extra triflate anion, are observed in the desorption chemical ionization mass spectra. Each oligomer within the available mass range is represented in the mass spectra. The formation of cluster ions in which a single, multiply-charged cation is associated with a number of singly-charged anions, as observed for these ammonium polysalts, is unusual. Five major and three minor series of positively charged ions are observed in DCI and DEI methods of ionization. Ions in the different series correspond either to cleavage at different bonds between the constituent monomers or to hydrogen transfer in different directions. Unique and structurally diagnostic fragmentation processes are observed in tandem mass spectrometry (MS/MS) experiments performed using collision activated dissociation of mass-selected oligomeric ions.