ESI and MALDI mass spectrometry of large POSS oligomers

Abstract

A series of Polyhedral Oligomeric Silsesquioxane (POSS) propylmethacrylate (PMA) and styryl oligomers were prepared from POSS monomers, R 7R'Si 8O 12, containing 1 functional R’ group for polymerization and 7 inert R-groups where R = isobutyl (i-butyl), phenyl (Ph), cyclohexyl (Cy) or cyclopentyl (Cp). Both standard atom transfer radical polymerization (ATRP) and free radical syntheses, the latter employing azoisobutylnitrile as the free radical initiator were used in the syntheses. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra were obtained in a new matrix, 4,4′-dihydroxyoctafluoroazobenzene which was especially designed for insoluble and intractable polymeric materials. Well-resolved series of oligomers were observed out to n = ∼13 in both the linear and reflectron modes. Major peaks were assigned based on tandem mass spectrometry (MSMS) fragmentation patterns to give a consistent explanation of the observed spectra. In all cases, ionization of the ATRP products gave cationized parent ions in which the terminal Br atom was replaced by hydrogen. Additional observed peaks were due to loss of POSS side chains from the oligomer backbone. The free radical products were terminated with either one or two isobutylnitrile groups. Electrospray ionization (ESI) spectra were more complex than the MALDI-TOF but showed either identical parent ions or closely related hydroxylated parent ions.