CHARACTERIZATION OF POLYDISPERSE SYNTHETIC-POLYMERS BY SIZE-EXCLUSIONCHROMATOGRAPHY MATRIX-ASSISTED LASER DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY/

Synthetic polymers baring 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 (S EC) with MALDI. Data are presented for a wide variety of synthetic pol ymers having polydispersities from 1.7 up to 3.0. Polystyrene (15 kDa and 48 kDa), polybutylacrylate (62 kDa), polycarbonate (28 kDa), aroma tic polyester resin (8 kDa) and a methyl methacrylate-methacrylic acid copolymer (34 kDa) were injected on a conventional SEC system with re fractive index (RI) or UV absorbance detection and 40 fractions collec ted over the polymer distribution. Ten fractions were analyzed by a MA LDI time-of-flight mass spectrometer operated in the continuons extrac tion linear mode, The m/z thus obtained were used as calibration point s for the SEC-RI system and allowed accurate calculation of the molecu lar Height averages M-w, M-n, M-z and the polydispersity for all the p olymers tested. The data for these entirely different polydisperse pol ymers were in good agreement with reference data from, for example, SE C with intrinsic viscosity detection. In addition, the choices of matr ix and cation for individual types of polymers are commented on, The e nd groups of the polymers Here determined from isotopically-resolved o ligomer spectra recorded by MALDI time-of-flight in the delayed-extrac tion reflectron mode. End groups proposed are compared with reference data from, amongst others, NMR and MALDI Fourier transform ion cyclotr on resonance-MS measurements. (C) 1997 by John Wiley & Sons, Ltd.