Post-source decay fragment ion analysis of polycarbonates by matrix assisted laser desorption ionization time-of-flight mass spectrometry

Post-source decay (PSD) experiments using a matrix-assisted laser desorptio n/ionization time-of-flight (MALDI-TOF) mass spectrometer have been applied to the structural determination of polycarbonates. We investigated linear and cyclic structures of polycarbonates derived from bisphenol A and a line ar and a cyclic polycarbonate derived from 4,4'-dihydroxydiphenyl-3,3-penta ne as well as a linear polycarbonate derived from bisphenol Z. The fragment ation behavior of these polycarbonates is similar to the mechanism proposed in the literature for electron impact and static secondary-ion mass spectr ometry measurements, but depends on the substituents bound to the central c arbon atom of the bisphenol unit. Knowing the fragmentation mechanism of po lycarbonates, the PSD-MALDI mass spectrum of a linear chain allows the mass es of both end groups to be infered. However, it is shown that variation of the substituent on the bisphenol unit has a strong influence on the fragme ntation behavior, so that cleavage of the polymer backbone may be suppresse d and the spectra are dominated by the loss of side chains.