| Abstract
| - The Ag+ adducts of polystyrene (PS) oligomers withdifferent sizes (6−19 repeat units) and initiating (α) orterminating (ω) end groups mainly decompose via freeradical chemistry pathways upon collisionally activateddissociation. This reactivity is observed for ions formedby matrix-assisted laser desorption/ionization as well aselectrospray ionization. With end groups lacking weakbonds (robust end groups), dissociation starts with random homolytic C−C bond cleavages along the PS chain,which lead to primary and benzylic radical ions containingeither of the chain ends. The primary radical ions mainlydepolymerize by successive β C−C bond scissions. Forthe benzylic radical ions, two major pathways are incompetition, namely, depolymerization by successive βC−C bond scissions and backbiting via 1,5-H rearrangement followed by β C−C bond scissions. The extent ofbackbiting decreases with internal energy. With short PSchains, the primary radical ions also undergo backbitinginvolving 1,4- and 1,6-H rearrangements; however, thisprocess becomes negligible with longer chains. If thepolystyrene contains a labile substituent at a chain end,this substituent is eliminated easily and, thus, not contained in the majority of observed fragments. Changes inthe PS backbone structure can have a dramatic effect onthe resulting dissociation chemistry. This is demonstratedfor poly(α-methylstyrene), in which backbiting is obstructed due to the lack of benzylic H atoms; instead, thisbackbone connectivity promotes 1,2-phenyl shifts in theprimary radical ions formed after initial C−C bond homolyses as well as H atom transfers between the incipientprimary and benzylic radicals emerging from these homolyses.
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