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 desorption/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 linear and a cyclic polycarbonate derived from 4,4′-dihydroxydiphenyl-3,3-pentane as well as a linear polycarbonate derived from bisphenol Z. The fragmentation behavior of these polycarbonates is similar to the mechanism proposed in the literature for electron impact and static secondary-ion mass spectrometry measurements, but depends on the substituents bound to the central carbon atom of the bisphenol unit. Knowing the fragmentation mechanism of polycarbonates, the PSD-MALDI mass spectrum of a linear chain allows the masses 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 fragmentation behavior, so that cleavage of the polymer backbone may be suppressed and the spectra are dominated by the loss of side chains.