A comparative study of three strategies used to synthesize well-defined carboxyl-end-capped polystyrenes is reported. Structural characterization was carried out using a combination of thin-layer chromatography (TLC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). For the reaction of polystyryl anions with 4-bromo-1,1,1-trimethoxybutane, in addition to the major product, Bu-PS-CH2CH2CH2COOH, four byproducts were observed. Their mass values suggest the following structures: Bu-PS-H, Bu-PS-CH3, Bu-PS-CH2CH=CH-CHO, and Bu-PS-CH2CH2CH2-CO-PS-Bu. The reaction of polystyryl anions with succinic anhydride generated the targeted compound, Bu-PS-CO-CH2CH2COOH, but also yielded the byproducts Bu-PS-H and dimer Bu-PS-CO-CH2CH2-CO-PS-Bu. Under appropriate conditions, the reaction of carbon dioxide gas with polystyryl anions could yield quantitative carboxyl chain-end-functionalization.