Novel procedure for molecular weight averages measurement of polydisperse polymers directly from matrix-assisted laser desorption/ionization time-of-flight mass spectra

A new method for the determination of reliable molecular weight averages (MW) and polydispersity index (MWD) values for polydisperse polymers, directly analyzing their matrix.assisted laser/desorption ionization time- of-flight (MALDI-TOF) mass spectra, is reported. Our success is due to the concerted effect of an off-line procedure of MALDI-TOF spectrum processing that includes: (i) signal smoothing to improve the recorded traces of the spectra up to high m/z values; (ii) a subtraction of the misleading contribution to the signals introduced by the offset used in spectrum recording; (iii) examination of the spectra up to the highest possible m/z value for a better accuracy in estimating the MW values. To illustrate this method, three polymers with a wide polydispersity index, a polydimethylsiloxane, a polymethylmethacrylate, and a bisphenol-A copolyether, have been analyzed. Contrary to the general opinion that MW values can be measured directly by MALDI-TOF only for polymers with a very narrow mass distribution, the data reported here show that our off-line procedure is also able to measure reliable MW values for polydisperse materials.