The use of silver tetrafluoroborate as a doping salt to achieve efficient and soft desorption/ionization of labile end-group-carrying polystyrene during electrospray ionization is demonstrated. Polystyrene carrying a dithioester end group prepared via reversible addition fragmentation chain transfer (RAFT) chemistry (using the RAFT agent cumyl phenyldithioacetate) as well as a commercial polymer standard prepared by anionic polymerization serve as model compounds. By employing silver tetrafluoroborate as ionization agent, an increase in ion count of more than one order of magnitude was achieved compared to ionization with sodium iodide. Little loss of the end group occurred via elimination of the dithioacid to yield vinyl-terminated polymer. A possible mechanism is given for catalysis of the cleavage reaction in the presence of silver salts. Side-product formation due to thermal or collision induced loss of the dithioester was kept at a minimum under optimized source conditions. Thus, we introduce a novel soft ionization protocol for polystyrenes, which are often difficult to ionize.