First Systematic MALDI/ESI Mass Spectrometry Comparison to Characterize Polystyrene Synthesized by Different Controlled Radical Polymerizations

Mass spectrometry techniques, specifically matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray ionization time-of-flight (ESI-TOF) are of considerable interest for characterizing very attractive polymers resulting from controlled radical polymerizations (CRP). This work proposes a systematic and experimental comparison of both ionization methods to analyze polystyrene prepared by five different CRP: nitroxide-mediated polymerization (mediated by N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)]nitroxide, known as SG1), atom transfer radical polymerization (Cl- and Br-mediated), reversible addition-fragmentation chain transfer polymerization, and reverse iodine transfer polymerization. All polystyrene chain end-groups obtained in each CRP-polymerization, and detected by both mass spectrometry techniques, are described and discussed. Elemental analyses of all CRP-polymers were also carried out to complete these results. It was found that the number of chain end-groups detected is higher by ESI-TOF than MALDI-TOF mass spectrometry in the polystyrene case. Furthermore, the cationization salt as well as the ionization source play a considerable role on the chain end-group fragmentation process occurring in mass spectrometer for the five CRP-polystyrenes. Concerning molecular weight considerations, the MALDI-TOF mass spectrometry is a better alternative to chromatography techniques than ESI-TOF mass spectrometry which under-estimates the average molecular weights.