DERIVATIZATION OF LOW-MOLECULAR-WEIGHT POLYMERS FOR CHARACTERIZATION BY MATRIX-ASSISTED LASER DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY/

Matrix-assisted laser desorption/ionization time-of-flight mass spectr ometry (MALDI-TOFMS) is shown to give inaccurate results for the analy sis of low molecular weight ethoxylate polymers, It is demonstrated th at when the degree of ethoxylation is low (n < 9), MALDI-TOFMS produce s substantially higher values for the number-average molecular weight (M(1)) than obtained with more classical methods such as NMR spectrome try and a wet chemical method to determine the hydroxyl number, Appare ntly, this is the result of discrimination of the former technique aga inst lower molecular weight ethoxylates in a polymer distribution, The results presented in this paper demonstrate this discrimination throu gh the analysis of a series of ethoxylates with progressively lower M( 1) values, It was also found that by derivatization of the polymer wit h phthalic anhydride, to produce the carboxylate derivative, the discr imination is reduced and data obtained with MALDI-TOFMS match more pre cisely the results obtained with the other methods. (C) 1997 by John W iley & Sons, Ltd.