Molecular Weight Determination and Structural Analysis in Polydisperse Polymers by Hyphenated Gel Permeation Chromatography/Matrix-Assisted Laser Desorption Ionization—Time of Flight Mass Spectrometry

A method for the determination of molecular weight distribution data for polydisperse polymer samples by MALDI-TOF is reported that involves the fractionation of polydisperse samples through analytical GPC columns and collection of fractions. Selected fractions are then analysed by MALDI-TOF and the mass spectra of these nearly uniform samples allow the determination of Mn and Mw averages. The GPC tracing, calibrated against molecular weight values obtained by MALDI, was used to compute molecular weight distribution data of the unfractionated sample. To test the reliability of the molecular weight estimates by the GPC/MALDI-TOF method, a sample of poly(methyl methacrylate) and two samples of poly(dimethyl siloxane), both with wide polydispersity, were analyzed. The results show that the molecular weights of PMMA fractions obtained by MALDI coincide with the GPC calibration plots obtained with anionic PMMA standards. In the case of the two poly(dimethyl siloxanes), two slightly different GPC calibration plots were obtained owing to the different structures of the polymer chains of the two samples. In fact, the MALDI spectra of low MW fractions of these polymers, showed that one sample consists essentially of linear oligomers, whereas the other sample contained cyclic oligomers.