CHARACTERIZATION OF POLYMERS BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY - MOLECULAR-WEIGHT ESTIMATES IN SAMPLES OF VARYING POLYDISPERSITY

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) allows the detection of large molecules such as those present in synthetic and natural macromolecules. Synthetic polymers may show a wide range of molecular weight distributions (MWD), according to the synthetic method used in their preparation. We have studied several poly(methylmethacrylate) (PMMA), poly(styrene) (PS) and poly(ethyleneglycol) (PEG) samples with varying MWD, and also a number of condensation polymers such as Nylon-6, poly(carbonate) and poly(ester). Measurements of MALDI-TOF spectra in the linear mode were used in our work to estimate the molecular weight (MW) and MWD of the polymer samples. Our results show that the molecular weight estimates provided by MALDI-TOF measurements agree with the values obtained by conventional techniques, such as gel-permeation chromatography (GPC), only in the case of polymer samples with very narrow molecular weight distribution. However, when the polydispersity reaches values around 1.10 the difference between the MW measured by GPC and measured by MALDI may amount to up to about 20%. At higher dispersions, the MALDI spectra fail to yield reliable MW values.