Modern mass spectrometry for coatings

Abstract

For the analysis of polymers soft ionization mass spectrometry, in which only molecular ions are observed, can provide the complete distribution of chains (length, composition, end-groups) in under ten minutes on microgram quantities of material. Moreover, molecular ion information of neat organic pigments or those present in crosslinked networks can also be furnished. No other analytical technique can supply these data in such a short time. The application of mass spectrometry to the characterization of materials used in today's high performance automotive coatings is presented. These include functional monomers, several acrylic copolymers, organic pigments and an epoxide prepolymer. While there are a variety of mass spectrometric techniques, in this paper we will highlight the techniques that we have found useful for the characterization of organic coating components. The selection of the mass spectrometric technique is dictated by the molecular weight of the material and to a lesser extent the chemical composition. We used potassium ionization of desorbed species (K+IDS) performed on a quadrupole mass spectrometer for materials under 1000 Daltons (Da). However, many of the ingredients used in current automotive finishes fall between 1000 and 10 000 Da. For these materials we used a Fourier transform mass spectrometer (FTMS) which is well suited for this mass range and boasts the highest resolution and mass accuracy available. Direct desorption/ionization using a carbon dioxide laser is our standard method of sample introduction. Recently, we coupled a gel permeation chromatograph to our FTMS using an electrospray ionization interface. This hyphenated technique offers one of the most powerful characterization methods for the coatings chemist.