Synopsis of the 2004 ASMS fall workshop on polymer mass spectrometry

Abstract

This year’s fall workshop of the American Society for Mass Spectrometry, which was held in Baltimore, Maryland last December 9-10, discussed synthetic polymer mass spectrometry and was chaired by Robert P. Lattimer (Noveon, Inc., Cleveland, Ohio, USA) and Chrys Wesdemiotis (University of Akron, Department of Chemistry, Akron, Ohio, USA). The workshop was co-sponsored by the Polymers Division of the National Institute of Standards and Technology (NIST) and follows polymer mass spectrometry workshops held at NIST in 2002 [1] and 2003 [2]. The format of the 2004 workshop was tutorial. Review-and-outlook talks were given in four major areas of polymer mass spectrometry (MS): Chromatographic Separations and MS, MS of Complex Compositions, Analysis of Polymer Surfaces, and MS Characterization of Polymer Structures. Each of the four sessions featured two invited speakers and was followed by a wide-ranging and lively panel discussion on the current and future directions of that area of polymer mass spectrometry. The presentations of the eight invited speakers will be summarized here. The first talk was given by Harald Pasch (Deutsches Kunstsoff Institut, Darmstadt, Germany) on “HPLCMALDI-TOF Mass Spectrometry for the Analysis of Complex Polymers.” Dr. Pasch’s central message was that polymer analysis cannot be performed by mass spectrometry alone but must be complemented by other techniques. He discussed the interplay between mass spectrometry and high-performance liquid chromatography (HPLC) (which separates on enthalpic differences) and size-exclusion chromatography (SEC) (which separates on entropic differences). The advantages of liquid chromatography under critical conditions (LCCC) (which separates polymer mixtures based on end-group functionality) were emphasized. Separations are needed to reduce the complexity of mass spectra, while the mass accuracy of MS is needed to calibrate the chromatography and help identify effluent components. Current work centers on coupling chromatography directly to matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry for rapid on-line separation and analysis. Kim R. Williams (Colorado School of Mines, Department of Chemistry and Geochemistry, Golden, Colorado, USA) spoke next on “Thermal Field-Flow Fractionation: A Polymer Separation Technique for MALDI-TOF MS.” After giving a tutorial on fieldflow fractionation (FFF), Prof. Williams discussed three ways to apply the force field necessary to separate polymer molecules: inertial, fluid flow, and thermal gradient. Using thermal FFF she gave examples of the separation of a wide array of polymer samples including simple polystyrene homopolymer standards, natural rubber, polystyrene-polybutadienepolytetrahydrofuran blends, and core-shell colloidal particles. Turning to the topic of coupling FFF to MALDI-TOF MS she discussed the use of mixed solvents to lower the working mass range of FFF (which generally performs better at high mass, typically greater than 100 ku) to overlap with the working mass range MALDI-TOF MS (typically used for polymers less than 100 ku). Once this had been accomplished a large number of possibilities opened up including applications of MALDI-TOF MS to calibrate FFF, and FFF separations of wide polydispersity polymers, polymer blends, copolymers, and coreshell polymer particles. The second session on MS of Complex Compositions began with a talk by Hajime Ohtani (Nagoya University, Nagoya, Japan) entitled “Complex Compositions of Polymeric Materials Studied by Pyrolysis-GC/MS.” The controlled pyrolysis of polymers in the mass spectrometer allows for the identification of the monomeric building blocks of complex macromolecules. By studying n-mers with n less than about four and separating them with gas chromatography the average tacticity of the polymer can be directly determined. The end groups can be identified in a similar fashion. Pyrolysis is especially important when the molecular mass of the polymer is so great that intact oligomers cannot be resolved by mass spectrometry. In this case breaking apart the polymer is the only way to resolve the end groups by MS. The degree of polymerization of high mass polymers can also be determined in this way by comparing the intensity of end-groups to that of mainchain monomers. Dr. Ohtani further described the application of pyrolysis to highly crosslinked polymers where placing intact molecules in the gas phase is impossible. In this case, gas chromatography mass spectrometry (GC-MS) allows for the determination of the degree of crosslinking by comparing the intensity ratio of cross-linked moieties vs. non-crosslinked moieties. The second talk in this session was given by Concetto Puglisi (Institute of Chemistry and Technology of PolyPublished online January 13, 2005