Sorption behavior of iodine vapor into pitches and its stabilizing mechanism below the melting temperature of the pitches Original Research Article

To elucidate the mechanism of the stabilization of pitches by iodine vapor below the melting temperatures of the pitches, the sorption or effect of introducing iodine into pitches and model-compounds was investigated using iodine sorption, Raman spectroscopy, 127I Mössbauer spectroscopy and gel permeation chromatography. Introduced/sorbed iodine was, at least, in two forms in the pitches: one formed charge-transfer complexes having strong interaction with molecules in pitches and the other weakly associated with the iodine in the complexes. The latter iodine seemed to be in a condensed state. Cata-condensed polycyclic molecules were polymerized with dehydrogenation and became larger molecules before forming charge-transfer complexes. On the contrary, peri-condensed polycyclic molecules easily produced charge-transfer complexes but showed no remarkable increase in their molecular weight. These increased the stability of the pitches even below their melting temperature.