| Both petroleum pitches and pitches derived from pure polycyclic aromatic hydrocarbons (PAHs) are oligomeric materials that can serve as precursors for a wide variety of advanced carbon materials. The goal of this study was the structural characterization and quantitative analysis of the dominant constituent oligomers and species present in these pitches.;A key requirement for such work is the ability to fractionate these complex mixtures into samples of narrow molecular weight distribution (mol wt; MWD) that can be used as standards. To this end, semicontinuous (or semibatch) dense-gas/supercritical extraction (DGE/SCE) was used to produce monomer, dimer, and trimer fractions of selected pitches (i.e., M-50 and pyrene pitch) during the course of this work. Matrix-assisted, laser desorption/ionization mass spectrometry (MALDI-MS) was then used to develop a reliable quantitative analysis method for these polydisperse mixtures of petroleum macromolecules. The interrelationships among MALDI sample preparation methods, analyte MWD, and MALDI response for well-defined, oligomeric pitch systems were investigated in order to identify a reliable sample preparation method. Based on the findings, solvent-free (vs. solvent-based) sample preparation was selected for the quantitative analysis study. DGE-derived, oligomeric cuts were used as standards, and the method of standard addition was successfully applied for the first time to the quantitative MALDI analysis of a polydisperse system using a solvent-free sample preparation method.;Advanced separation and analytical characterization techniques were used to determine the molecular structures of the constituent species present in the monomer and dimer fractions of a thermally polymerized petroleum pitch, and of a catalytically polymerized pyrene pitch. Even though the starting material for the pyrene polymerization was pure pyrene, alkylated species were found to be present, albeit at low concentrations. Alkylpyrene isomers and the pyrene dimer isomer were isolated by DGE followed by HPLC and then unambiguously identified via MALDI and UV-vis. Dimer species were found to consist exclusively of monomer units connected by 6-membered rings. This is in dramatic contrast to our experience with both anthracene and petroleum pitches formed via thermal polymerization, where 5-membered connecting rings are the predominant method of polymerization. |
