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 averag es (MW) and polydispersity index (MWD) values for polydisperse polymer s, directly analyzing their matrix-assisted laser/desorption ionizatio n 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 spe ctrum processing that includes: (i) signal smoothing to improve the re corded traces of the spectra up to high m/z values; (ii) a subtraction of the misleading contribution to the signals introduced by the offse t used in spectrum recording; (iii) examination of the spectra up to t he highest possible m/z value for a better accuracy in estimating the MW values. To illustrate this method, three polymers with a wide polyd ispersity index, a polydimethylsiloxane, a polymethylmethacrylate, and a bisphenol-A copolyether, have been analyzed. Contrary to the genera l opinion that MW values can be measured directly by MALDI-TOF only fo r polymers with a very narrow mass distribution, the data reported her e show that our off-line procedure is also able to measure reliable MW values for polydisperse materials.