MESOPHASE FORMATION IN SYNTHETIC PITCHES: AN INVESTIGATION OF THE EFFECTS OF CHEMICAL STRUCTURES ON MESOPHASE FORMATION

Simple 2 to 4-ring polynuclear aromatic compounds were reacted to produce synthetic pitches for study of the effects of chemical structure on mesophase formation. With a known starting material, the reactivities of different sites of model compounds, the molecular weight, the C/H ratio, and spectra studies, the structure of these pitches can be better defined than with pitches produced from petroleum.;Solvent fractionation techniques were used to obtain cuts from the synthesized pitches. The mesophase formation of these fractions was studied by heat-treatment and metallographic examination. The chemical structures of these fractions were hypothesized.;Four mechanisms were proposed for mesophase formation, namely: (1) building-up of molecular weight, (2) cracking-off of the disruptive alkyl side arms, (3) volatilization of the low molecular weight species, and (4) ring fusion. Ladder-type molecule pitches form mesophase much easier than disc-like molecules. Polyphenyl pitches were essentially isotropic. The polyphenyls tend to form less condensed, non-polar structures which are a deterrent to mesophase formation. The disc-like molecules have a relatively high C/H ratio. Due to this high C/H ratio, disruptive low molecular weight species are difficult to remove by solvent fractionation techniques. Mesophase formation does not occur easily.;The critical structures for mesophase in pitch were determined from samples that were heat-treated to form tiny mesophase spheres. The critical molecular weight and C/H ratio of simple 2 to 4-ring compounds are found to range from 700 to 900 and 1.70 to 2.15, respectively.;Both catalytic and pyrolytic syntheses were performed. The pyrolytic syntheses, which were run in an autoclave, were calculated to occur in the liquid phase except for naphthalene. All catalytic syntheses involved liquid phase reactions, since the reaction temperatures are lower than the atmospheric boiling point of the compounds. Two component syntheses were also carried out.;Molecular weight distribution is also important for mesophase formation. The low molecular weight species inhibit mesophase formation, while the high molecular weight species are essential for mesophase formation.