Element-substituted polyaromatic mesophases: I. Boron-substitution with the pyridine-borane complex

Abstract

The synthesis of a boron-substituted polyaromatic mesophase was studied by copyrolysis of a filtered coal tar pitch with pyridine-borane under a 1 MPa argon atmosphere. The pyrolysis temperature was varied between 360 and 420 °C, the boron content of the pitch-pyridine-borane mixture was increased step by step up to 5%. Pyridine-borane is decomposed above 120 °C; the pyridine is volatilized, and the highly volatile borane immediate reacts with the aromatics, preferentially by hydroboronation. Formation of the mesophase is accelerated; it is already high-grade spherulitic with small boron additions; with 5% boron the pyrolysis product is nearly isotropic. These boron-substituted mesophases are potential precursors for the production of boron-substituted sintered carbons.