Four bromine- and phosphonium-terminated polystyrenes were analyzed by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) using covalent cationization. Bromine-terminated polystyrenes were prepared by atom transfer radical polymerization (ATRP) giving narrow molar mass (MM) distributions with number-average molar mass ranging from 2 to 40 ku. The resultant bromine end group was converted to a phosphonium ion. Precharging the polymer by covalent cationization is an alternative approach to traditional metal cationization for MALDI-MS polymer analysis. MALDI-MS, gel permeation chromatography, and proton nuclear magnetic resonance analyses confirmed ATRP synthesis and end group modification of the polystyrenes. High performance liquid chromatography at the critical point of adsorption was used to determine a phosphonium salt conversion between 37% and 90%. Similar MMs and MM distributions determined by MALDI-MS analysis were observed for Br-terminated polystyrene ionized using traditional metal cationization and the covalently cationized (i.e., phosphonium-terminated) polystyrene. Covalently cationized samples yielded better data quality than the Br-terminated samples. Higher signal intensity and signal reproducibility were observed for the covalently cationized samples using milder laser conditions.