Tandem Mass Spectrometry Characteristics of Silver-Cationized Polystyrenes: Backbone Degradation via Free Radical Chemistry

The [M + Ag]+ ions of polystyrene (PS) oligomers are formed by matrix-assisted laser desorption/ionization, and their fragmentation characteristics are determined by tandem mass spectrometry experiments in a quadrupole/time-of-flight mass spectrometer. Collisionally activated dissociation (CAD) of [M + Ag]+ starts with random homolytic CC bond cleavages in the PS chain, which generate radical ions carrying either the initiating (an•, bn•) or the terminating (yn•, zn•) chain end and primary (an•, yn•) or benzylic (bn•, zn•) radical centers. The fragments ultimately observed arise by consecutive, radical-induced dissociations. The primary radical ions mainly decompose by monomer evaporation and, to a lesser extent, by β-H• loss. The benzylic radical ions primarily decompose by 1,5-H rearrangement (backbiting) followed by β C−C bond scissions; this pathway leads to either closed-shell fragments with CH2 end groups, internal fragments with 2−3 repeat units, or truncated benzylic bn•/zn• radical ions that can ...