Molecular Weight Distribution of Living Chains in Polystyrene Prepared by Atom Transfer Radical Polymerization

Abstract

Living and dead chains of a polystyrene synthesized by atom transfer radical polymerization were separated and characterized by high performance liquid chromatography (HPLC), size exclusion chromatography (SEC), NMR, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The bromine end group in the living chain was quantitatively converted to a hydroxyl end group via first azidation and subsequent copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction with propargyl alcohol. The living chains bearing a polar end group are fully resolved from the unmodified dead chains by HPLC separation using a bare silica stationary phase. Molecular weight distributions (MWD) of the living and dead chain are characterized by SEC and MALDI-MS. The MWD of the living chains is close to a Poisson distribution. Interestingly, the elution peak of the living chains in the HPLC separation split into two. The peak split is attributed to the diastereomeric structure of the chain end by NMR and MALDI-MS analyses.