Preparation and modulation of naphthalene oligomers catalyzed by chloroaluminate ionic liquids for advanced mesophase pitch production

Abstract

Mesophase pitch is a crucial compound platform for the production of various advanced carbon materials, with its quality significantly influenced by the composition and structure of precursor materials. Here, we present a novel method for preparing naphthalene oligomers (NOs), which serve as precursors for the preparation of mesophase pitch (MP) via naphthalene polymerization catalyzed by chloroaluminate ionic liquids (Al-ILs). Different from those obtained via AlCl₃-catalyzed method, the NOs synthesized by Al-ILs possess a narrow molecular weight distribution (MWD, 200–600 Da) and a well-defined molecular composition (di-, tri-, and tetra-polymers of naphthalene). When the prepared NOs were used as precursors, the resulting MP exhibited a shorter polycondensation time (4 h), higher yield (68%), lower ash content (0.005%), more concentrated MWD, and easier carbonization. These improvements are attributed to the tunable structure and acidity of Al-ILs, which facilitate naphthalene polymerization at low reaction temperatures and appropriate acidity, thereby improving its controllability. This work provides a flexible and efficient pathway for the custom production of NOs that potentially enable broader industrial applications of MP.