MALDI-TOF MS characterization of polystyrene synthesized by ATRP

In this work, we investigated the peculiar peaks found in the MALDI-TOF mass spectra of polystyrenes (PS) with a bromine end prepared by atom transfer radical polymerization when silver trifluoroacetate (AgTFA) and THF were used as cationization agent and solvent, respectively, in the MALDI sample preparation. In the MALDI mass spectrum, PS with a terminal bromine was not detected but the species with a terminal double bond (U series), and -22 m/z (T series) and +18 m/z (W series) peaks relative to U series appeared as major peaks. While the U species was reported as a result of the elimination reaction of HBr, but the origin and the structure of the other species have not been elucidated. We found that the -22 m/z peak of U_n is in fact T_n-2, which is the adduct of THF and the anion of the Ag salt, TFA^- (+186 m/z) to U_n-2. The +18 m/z peak was confirmed to be the species with a terminal OH. All these reactions were catalyzed by Ag salt and the T and W series were not found at all when NaTFA was used as a cationization agent.