Characterization of Polyesters by Matrix-Assisted Laser Desorption/Ionization and Fourier Transform Mass Spectrometry

Abstract

Two homopolyesters, poly(neopentyl glycol- alt-isophthalic acid) and poly(hexanediol- alt-azelaic acid), and two copolyesters, poly[dipropoxylated bisphenol-A- alt-(isophthalic acid- co-adipic acid)] and poly[neopentyl glycol- alt-(adipic acid- co-isophthalic acid)] were analyzed by internal-source matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FT-MS). The high resolution and high mass accuracy provided by FT-MS greatly facilitate the characterization of the polyester and copolyester samples. Isobaric resolution allows the ion abundances of overlapping isotopic envelopes to be assessed. Repeat units were confirmed and end group functionality assigned. Single-shot mass spectra of the entire polymeric distribution demonstrate that the dynamic range of this internal MALDI source instrument and the analyzer cell exceeds the performance previously reported for higher field instruments. Corrections of space–charge mass shift effects are demonstrated for the analytes using an external calibrant and (subsequent to confirmation of structure) using internal calibration, which removes the ambiguity due to space–charge differences in calibrant and analyte spectra. Capillary gel-permeation chromatography was used to prepare low polydispersity samples from a high polydispersity polyester, improving the measurement of molecular weight distribution two-fold while retaining the benefits of high resolution mass spectrometry for elucidation of oligomer identity.