Polybenzimidazole Aerogels with High Thermal Stability and Mechanical Performance for Advanced Thermal Insulation Applications

Abstract

Advancements in the development of high-performance organic aerogels are essential for cutting-edge thermal insulation applications, where lightweight and durable structures, low thermal conductivity, and exceptional thermal stability are critical requirements. In this work, we present thermally stable and mechanically robust organic aerogels based on cross-linked benzimidazole-rich structures, specifically designed for thermal insulation. These aerogels exhibit a combination of valuable properties, including low density, large specific surface area and high porosity. Their tortuous mesoporous structures effectively reduce heat transfer by limiting gas-phase conduction, resulting in thermal conductivities as low as 23.9 mW m^-1 K^-1. This is coupled with a remarkable resistance to thermal decomposition (Td_1% > 500 °C), surpassing the stability of the original polymer precursor (OPBI). Additionally, the strong polymer network, reinforced by both covalent and noncovalent interactions, provides exceptional mechanical strength, allowing the aerogels to withstand substantial loads without fracturing. This unique combination of low density, high porosity, robust mechanical performance, and superior thermal stability makes these aerogels highly promising for demanding thermal insulation applications, such as thermal protection for space exploration vehicles, fire-resistant suits, and EV battery insulation.

Keywords: aerogels; insulation; polybenzimidazole; thermal insulation; thermal stability.

1

Model reaction between DBX and benzimidazole, with the corresponding ¹H NMR of the model compound, BIM.

2

(a) Aerogel formation (OPBI-A) by the cross-linking reaction of poly-2,2′-p-oxidiphenylene-5,5′-dibenzimidazole (OPBI) with α,α′-dibromo-p-xylene (DBX). The network is stabilized through covalent and noncovalent interactions. (b) Representative photographs of the aerogel synthesis process. In the final two images, the light and robust nature of the aerogels is highlighted, as the same sample that rests on a piece of cotton can also withstand more than 2500 times its own weight (1 kg).

3

(a) N₂ adsorption and desorption isotherms of OPBI-As at 77 K. (b) BJH pore size distribution of OPBI-As. (c) Fiber diameter distributions based on 100 fibers; SEM pictures and ImageJ software were used. (d) SEM pictures of OPBI-As (see Figure S3, Supporting Information, for range of magnifications).

4

(a) Thermal conductivity values of OPBI-As in comparison of other benzimidazole based aerogels − and commercial thermal insulation materials of ranging bulk densities. (b) Top-view IR images of OPBI-A1 placed on hot (120 °C) and cold (−20 °C) stage at the beginning and after 10 min (c) TGA curves under N₂ flow. (d) OPBI-A1 subjected to ethanol flame. (e) Cross-section of OPBI-A1 after flame tests. (f) SEM picture of the OPBI-A1 cross-section after flame tests (100 μm bar). (g) SEM pictures of charred layer (top) and porous interior (bottom) of OPBI-A1 after flame tests.

5

(a) Photograph of OPBI-A1 (ρ_b = 68 mg cm^–3, 95% porosity) supporting more than 2500 times its own weight (1 kg). (b) Stress–deformation curves of OPBI-As. Three identical samples were used for each measurement with their corresponding graphs being presented in Figure S4a. (c) Comparative picture of OPBI aerogel before and after compression to 50% deformation.