CHEMICAL-BOND FORMED IN THERMALLY POLYMERIZED PETROLEUM PITCH

The type of chemical bond joining the monomers in thermally polymerized petroleum pitch derived from a decant oil was investigated using wet chemical, gel permeation chromatography, pyrolysis gas chromatography, and H-NMR techniques. Reaction of mesophase pitch with a depolymerizing agent did not result in depolymerization of pitch dimers to pitch monomers, which indicates the absence of methylene bridges. Quantitative studies of the thermal cracking and gas formation reactions of alkyl groups on the large aromatic molecules (> 400 amu) present in mesophase pitch indicate that the side chains (methyl through butyl) fracture at the alpha position to the aromatic ring, which leads to the formation of aryl-aryl bridges in the pitch dimers. In contrast to these results, the cracking of side chains in small benzene-substituted molecules, occur preferably at the beta position to the ring, which leads to the formation of methylene bridges in the produced dimers.