Spectroscopic Insight into the Dissolution Mechanism of Polybenzimidazole in N,N-dimethylacetamide/lithium Chloride

The N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) solvent system is one of the most effective solvents for polybenzimidazole (PBI). Despite its widespread industrial application in PBI processing, the dissolution mechanism at the molecular level remains poorly understood. In this work, the model compound PhBI was employed to investigate the interactions within the PBI/DMAc/LiCl solution via Fourier-transform infrared (FTIR) spectroscopy and multinuclear NMR spectroscopy (1H, 7Li, 13C, and 35Cl). The results demonstrate that upon dissolution of PBI in the DMAc/LiCl system, Cl− ions insert into the PBI chains and establish NH⋯Cl− hydrogen bonds with the imino protons. This interaction disrupts the original hydrogen-bonding network of PBI while simultaneously inducing the dissociation of tightly bound Li+-Cl− ion pairs. To maintain charge balance, Li+ ions, together with coordinated DMAc molecules, are attracted along the PBI chains, leading to the dispersion of the PBI chains and the formation of a homogeneous solution. Through a model analogy approach, this work elucidates the intermolecular interactions governing PBI dissolution in DMAc/LiCl and infers the underlying dissolution mechanism. These findings provide critical insights for understanding and optimizing PBI dissolution conditions, enhancing industrial processing techniques, and designing novel solvent systems for PBI.