Hydrogen‐Bonding Interactions and Molecular Packing in Polyimide Fibers Containing Benzimidazole Units

Abstract

Rigid-rod polyimides (PI) containing benzimidazole moieties were synthesized and spun into fibers by a wet-spinning method. The resultant fibers exhibited an optimum tensile strength of 2.15 GPa and an initial modulus of 105 GPa with a low elongation of 2.2%. The PI fibers consisting of various ratios of 2,2 0 -bis(trifluoromethyl)-4,4 0 -diaminobiphenyl (TFMB) and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) were investigated by Fourier transform infrared spectroscopy and two-dimensional wide angle X-ray diffraction (2D WAXD). Direct evidence of hydrogen-bonding involving the N-H groups of BIA and the imide carbonyls is presented. Qualitative and quantitative information of this molecular interaction was obtained and discussed. This has been considered as a main factor responsible for the significantly improved mechanical properties of the PI fibers. 2D WAXD and molecular mechanics modeling were used to simulate the structure of the aromatic PI fibers. As a result, the addition of BIA in the main chains is to increase the regularity of the molecule packing, which plays an important role in the enhanced strength of the PI fibers with more BIA loadings.

A facile assembly of polyimide/graphene core–shell structured nanocomposites with both high electrical and thermal conductivities

“…Considering the existence of imide group in the PI chain, hydrogen bonding could be easily introduced into PI system, which would not only enhance the interaction between grapehene and polymer, but also improve the mechanical and other properties of polyimide [53][54][55]. What's more, the synergistic effect of hydrogen bonding and p-p stacking interaction would lead to a unique spontaneous self-assembly of polyimide macromolecule and form nanoparticles with a dimple-like morphology [56].…”

Structures and properties of polyimide fibers containing ether units

“…Generally, the introduction of specific groups into the polymer backbone has been considered as a typical approach to modify the chemical structure of PI fibers, as outstanding properties of individual group could be integrated to form new high-performance polymers [19,20]. So far, in order to improve mechanical properties of PI fibers, the monomers contain rigid aromatic heterocyclic units, such as 2-(4-aminophenyl)-6-amino-4(3H)-quinazolinone (AAQ), 2,5-bis(4-aminophenyl)-pyrimidine (2,5PRM), and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), are preferred to increase the rigidity of the polymer chain and introduce additional intermolecular associations [10,21,22]. For example, a series of PI fibers containing AAQ moiety were prepared by Niu et al with the tensile strength and modulus up to 2.8 and 115.2 GPa, respectively.…”

Effect of molecular rigidity and hydrogen bond interaction on mechanical properties of polyimide fibers

“…Tensile strength of 0.5 GPa is enough for PI fibers in this area. However, many researchers hope to use PI fibers in advanced composite materials due to their excellent radiation resistance and high thermal properties . Tensile strength of fibers used in advanced composite materials should be above 2.5 GPa at least.…”

“…Many researchers have demonstrated that PI fibers with more rigid backbones lead to more excellent mechanical properties. As an alternative approach, benzimidazole units are introduced into the PI main chain by many researchers in recent years . For example, in our previous work, a series of copolyimide (co‐PI) fibers containing benzimidazole moieties in the PI main chains were prepared.…”

“…Dong et al . prepared a type of PI fiber based on 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl (TFMB), 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (BIA) and BPDA, showing a tensile strength of 2.15 GPa with a modulus of 105 GPa . Consequently, PI fibers containing benzimidazole units have the potential to become representative of PI fibers with high strength and modulus for enhancement of intermolecular interactions …”