Structural features and formation mechanism of soluble fractions of mesophase pitch derived from 1,2,4,5-tetramethylbenzene methylene-bridged oligomer

Abstract

A mesophase pitch which has 100 vol.% anisotropic content, low softening point, high solubility and good fluidity was prepared at relatively low temperature from 1,2,4,5-tetramethylbenzene oligomers cross-linked by methylene bridges and subsequent heat treatment. Electron impact mass spectrometry, field desorption mass spectrometry and 1H and 13C nuclear magnetic resonance etc. were used to characterize the structural features of soluble fractions of the mesophase pitch. The results show that the mesophase pitch contains many methyls and some amount of naphthenic groups. The molecules in mesophase pitch appear to have kata-type aromatic skeleton. The mechanism of mesophase pitch formation involves intramolecular reactions, and the occurrence of internal oligomer condensation causes the formation of polyacenes which successively di- and trimerize through adjacent methyls to form long-chain kata-type polyaromatics with naphthenic structures. These structural characteristics favour mesophase with excellent properties.