Gradient-Structured Nonflammable Flexible Polymer Membranes

Herein, we report the formation and properties of a rare example of high-performance composite membranes from polybisbenzimidazobenzophenanthroline-dione (BBB) that do not sustain a flame or burn with smoke nor show melt dripping. In addition, this material possesses a low density and very high thermal stability (char yield as high as 80-94%), strength, and flexibility. Such membranes are highly desirable for battery separators, protective clothing, construction, and automobiles. Because BBB is an insoluble and infusible polymer, the composite membranes were made using a bottom-up vacuum-assisted self-assembly method with an aqueous dispersion of short BBB fibers and Hec. The use of water as the solvent, upscalability, and excellent flame retardancy in combination with low density, flexibility, and low thermal conductivity of the composite membranes make the preparation method and membranes highly promising for future use in real applications.