SOLID-STATE C-13 NMR AND HIGH-TEMPERATURE H-1-NMR DETERMINATION OF BULK STRUCTURAL-PROPERTIES FOR MESOPHASE-CONTAINING SEMI-COKES PREPARED FROM COAL-TAR PITCH

A series of semi-cokes, containing from virtually 0 to 100% mesophase, were produced from the THF-soluble fraction of a soft coal tar pitch. The mesophase contents were estimated by high temperature in situ H-1 NMR and optical microscopy with extremely close agreement being obtai ned between the two techniques. Quantitative solid state C-13 NMR meas urements using the single pulse excitation technique indicated that th e extent of anisotropy in the pitch is a function of the condensation of the aromatic structure, where isotropic pitches contain 5-6 rings o n average, assuming pericondensation, which increases to 9-10 rings fo r the fully converted mesophase pitches. Characterisation of the pyrid ine-solubles (PS) and insolubles (PI) from the pitches confirmed that development of mesophase in the coal tar pitch is limited by the loss of low molecular mass compounds, in that the PS contain 5-6 rings thro ughout the series while the PI, even in largely the initial isotropic state, are as condensed as in the anisotropic pitches. (C) 1998 Elsevi er Science Ltd. All rights reserved.