The key molecular species present in model pyrene pitches both thermally and catalytically polymerized from pyrene have been unambiguously identified.  Packed-column, dense-gas extraction, using supercritical toluene as the solvent and NMP as the co-solvent, was used to fractionate the pitches into pure monomer, dimer, and trimer cuts.  An unexpected benefit of the use of NMP is that it was found to suppress the condensation reaction between toluene and the pyrene oligomers � apparently by forming a Lewis acid�base complex with the AlCl3 catalyst � that can occur in the extraction column at temperatures above 350 �C.  The resultant fractions were then analyzed for molecular-structure information via matrix-assisted, laser desorption/ionization (MALDI) mass spectrometry and by HPLC with UV-vis detection. Results indicate that there are significant differences between the products of catalytic vs. thermal polymerization of pyrene.  For example, catalytic polymerization is highly selective with respect to isomerization, with only one of the two possible isomers of pyrene dimer, that is, 1.14,7.8-dibenzoperopyrene, being present.  In addition, alkylation of the pyrene monomer, dimers, trimers, and tetramers occur during the catalytica polymerization process.  On the other hand, no such alkylation occurs during thermal polymerization, and oligomers are formed by connecting the monomer units by 5-membered rings (vs. 6-membered rings that dominate catalytically).

Fractionation and characterization of oligomeric pyrene pitches via supercritical extraction

245th National Meeting (2013)

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