Structural characterization of aromatic polyester resins by matrix-assisted laser desorption/ionization mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry was u sed to characterize average molecular weights and end-groups of synthetic a romatic polyesters and the same characteristics were also determined for ac etylated polyester samples. In addition, the progress of a polyesterificati on reaction was followed by mass spectrometry by investigating samples take n from the reaction mixture at different reaction times. Average molecular weights were compared with those measured by gel-permeation chromatography (GPC) and the results of quantitative end-group analysis were considered wi th the acid values of the polyesters. MALDI measurements were carried out u sing two different matrix compounds, 2,5-dihydroxybenzoic acid (DHB) and 2- (4-hydroxy-phenylazo)benzoic acid (HABA). Different matrices and derivatiza tion of the polyester influenced the width of the polymer distribution dete rmined by mass spectrometry and further affected the proportions of differe ntly terminated oligomers, in addition to the average molecular weight. The relative amount of the most abundant oligomer species was increased when t he polymer distribution width was increased.