Characterization of low molecular weight poly(acrylic acid) samples by capillary supercritical fluid chromatography and capillary supercritical fluid chromatography–mass spectrometry

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Abstract
Low molecular weight poly(acrylic acid) (PAA) samples were derivatized to increase their solubilities in the supercritical mobile phase, CO2. tert‐Butyldimethylsilyl ester derivatives provided better chromatographic performance and molecular weight range than did trimethylsilyl or methyl esters. Individual oligomers were resolved through approximately n = 28. Higher oligomers, up to approximately n = 45 (corresponding to an underivatized molecular weight of more than 3300), were eluted from the column but were not resolved. Ammonia chemical ionization and electron ionization supercritical fluid chromatography–mass spectrometry data revealed that the PAA terminal groups of the samples studied were sulfonate and hydrogen.