MALDI-TOF MS characterization of carboxyl-end-capped polystyrenes synthesized using anionic polymerization

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-CH ₂CH ₂CH ₂COOH, four byproducts were observed. Their mass values suggest the following structures: Bu-PS-H, Bu-PS-CH ₃, Bu-PS-CH ₂CH=CH-CHO, and Bu-PS-CH ₂CH ₂CH ₂-CO-PS-Bu. The reaction of polystyryl anions with succinic anhydride generated the targeted compound, Bu-PS-CO-CH ₂CH ₂COOH, but also yielded the byproducts Bu-PS-H and dimer Bu-PS-CO-CH ₂CH ₂-CO-PS-Bu. Under appropriate conditions, the reaction of carbon dioxide gas with polystyryl anions could yield quantitative carboxyl chain-end-functionalization.