Characterization of polydisperse synthetic polymers by size-exclusion chromatography/matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Abstract

Synthetic polymers having a polydispersity greater than 1.1 cannot be reliably characterized by matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry alone. This complication has been overcome by off-line coupling of size-exclusion chromatography (SEC) with MALDI. Data are presented for a wide variety of synthetic polymers having polydispersities from 1.7 up to 3.0. Polystyrene (15 kDa and 48 kDa), polybutylacrylate (62 kDa), polycarbonate (28 kDa), aromatic polyester resin (8 kDa) and a methyl methacrylate–methacrylic acid copolymer (34 kDa) were injected on a conventional SEC system with refractive index (RI) or UV absorbance detection and 40 fractions collected over the polymer distribution. Ten fractions were analyzed by a MALDI time-of-flight mass spectrometer operated in the continuous extraction linear mode. The m/z thus obtained were used as calibration points for the SEC-RI system and allowed accurate calculation of the molecular weight averages Mw, Mn, Mz and the polydispersity for all the polymers tested. The data for these entirely different polydisperse polymers were in good agreement with reference data from, for example, SEC with intrinsic viscosity detection. In addition, the choices of matrix and cation for individual types of polymers are commented on. The end groups of the polymers were determined from isotopically-resolved oligomer spectra recorded by MALDI time-of-flight in the delayed-extraction reflectron mode. End groups proposed are compared with reference data from, amongst others, NMR and MALDI Fourier transform ion cyclotron resonance-MS measurements. © 1997 John Wiley & Sons, Ltd.