ELECTROSPRAY IONIZATION TIME OF FLIGHT MASS SPECTROMETRY OF POLY(METHYL METHACRYLATE) AND POLYSTYRENE USING SURFACE ACTIVE QUATERNARY AMMONIUM SALTS

Abstract

Electrospray ionization time of flight mass spectrometry (ESI-ToF-MS) is a powerful characterization technique for large nonvolatile compounds, but has found limited applicability in the synthetic polymer field. Two factors currently limit the utility of ESI-ToF-MS for synthetic polymer characterization: 1) Electrospray ionization often results in multiply charged species for each component in the sample. Synthetic polymers contain a distribution of many compounds with close, uniformly spaced masses. The presence of multiple m/z peaks for each mass typically results in data that is complicated and becomes increasingly complicated as the average molar mass of the sample increases. 2) Electrospray ionization is best suited for polar, easily ionized species dissolved in polar solvents. The vast majority of synthetic polymers are relatively non-polar, do not ionize easily and are not soluble in the polar solvents most often used for ESI. By adding easily ionizable, surface active quaternary ammonium salts that associate with polymer molecules during ionization, we have made significant strides in overcoming both of these limitations. By using cetyltrimethylammonium bromide (CTAB) as an additive, we have been able to produce ESI-MS spectra with only singly charged charge states for the entire m/z range observable by our instrument (m/z = 0 - 20,000). Data will be presented for poly(methyl methacrylate) and polystyrene samples. Weight averaged molecular weight (Mw), number averaged molecular weight (Mn) and polydispersity (PD) calculations were all in good agreement with comparative analysis using Gel Permeation Chromatography (GPC) and Gel Permeation Chromatography - Multi-Angle Light Scattering (GPC-MALS). Further, for some samples, multiple distributions were identified corresponding to different end groups highlighting the utility of this approach.