Structure‐Property Relationship of Polyimide Fibers with High Tensile Strength and Low Dielectric Constant by Introducing Benzimidazole and Trifluoromethyl Units

Abstract

Copolyimide (co‐PI) fibers with high strength and low dielectric constant are synthesized and prepared by introducing 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl (TFMB) and 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (BIA) diamines into the rigid backbones. The resultant fibers not only exhibited excellent mechanical properties with a tensile strength of 2.627 GPa and an initial modulus of 96.786 GPa, but also possessed a dielectric constant as low as 2.433 at 10 GHz. The existence of intermolecular hydrogen‐bonding interaction is confirmed by Fourier transform infrared spectroscopy, which has been considered as the leading factor responsible for the significantly improved mechanical properties of the co‐PI fibers. 2D wide‐angle X‐ray diffraction (2D WAXD) is adopted to investigate the variation on the aggregation structure of PI fibers after the incorporation of fluorine group. The fibers with more TMFB content possessed a higher orientation degree together with a larger free volume fracture due to the combined effects of enhanced flexibility and the volume effect of trifluoromethyl groups. Meanwhile, the prepared PI fibers exhibit a 5% weight loss temperature ranging from 543 to 533 °C in the nitrogen atmosphere and a glass transition temperature ranging from 334 to 317 °C, revealing high thermal stability of co‐PI fibers.

Preparation and Interfacial Properties of Hydroxyl-Containing Polyimide Fibers

“…When more HAB is introduced, the peak position of V (sym)C=O on cyclic imide continuously shifts from 1704 cm −1 to 1699 cm −1 , as shown in Figure 1 c 1 , i.e., the red shift, which is similar to that in the studies by Lian et al showing that the red shift of C=O would occur upon the formation of H-bonding [ 39 ]. To evaluate the contribution degree of -OH to intra-/intermolecular H-bonding associations, curve-fitting ATR-FTIR spectroscopy in the range from 1650 cm −1 to 1750 cm −1 can be applied to quantitatively analyze H-bonding associations based on the previous studies [ 23 , 25 ]. As depicted in Figure 1 c 2 –c 6 , four peaks are separately identified for the BPHB–0 fiber, and the BPHB–1, 3, 5, and 7 fibers have five peaks.…”

“…Similarly, the peaks at 2 θ = 10.2°, 16.9°, 22.0°, 27.3°, and 31.4° for the BPHB–7 fiber are assigned to the (002), (003), (004), (005), and (006) planes, respectively, because the repeat length of the BPDA/HAB trimer ( Figure 2 h) is 1.899 nm. Obviously, the diffraction angle of the (002) plane gradually decreases from 11.5° (BPHB–0) to 10.2° (BPHB–7) with the increase in d -spacing ( Table 3 ), implying that some BPDA/ p -PDA units are replaced by larger BPDA/HAB units [ 25 ].…”

“…Bao et al [ 24 ] introduced an HBOA diamine containing an -OH group into the BPDA/PRM macromolecular chain; meanwhile, the tensile strength and modulus of resultant fibers surprisingly reached 4.15 GPa and 125.93 GPa, respectively. To meet the requirements of wave-transparent composite reinforcement, Wang et al [ 25 ] selected the TFMB diamine-containing -CF 3 group and then introduced it into the BPDA/ p -PDA/BIA polymer chain. The prepared PI fibers not only exhibited excellent mechanical properties (tensile strength of 2.62 GPa and modulus of 96.78 GPa), but also possessed a dielectric constant as low as 2.433 at 10 GHz.…”

Preparation and characterization of porous polyimide fibers with electromagnetic wave absorption properties

“…The ordered arrangement of molecular chains plays an considerable role in the mechanical properties of aromatic PI/C-Fe composite fibers. [45][46][47] Figure 4 shows the mechanical properties of the fiber and its orientation degree, when the temperature of coagulation bath is 10 C, the orientation degree is 87.03% and the tensile strength of the PI-C/Fe composite fiber is 299.42 MPa, the tensile modulus is 14.72 GPa. As the temperature of coagulation bath gone up, the orientation of ordered part also showed a trend of gradual decrease, and the mechanical properties of PI-C/Fe composite fiber showed a same trend, in line with the general rule that mechanical properties of fiber are positively correlated with orientation.…”

Construction of porous poly (aryl sulfide sulfone) film with low dielectric constant and excellent mechanical property

“…Over the past decades, lots of efforts have been focused on the fabrication of low dielectric constant film. The main methods include: (1) Designing the molecular structure of the polymer to reduce the polarizability via introducing groups or side chains with strong polar fluorine atoms 5–8 or adding more functional groups with large free volume, 9–12 such as naphthyl, fluorenyl, and spiral ring; 13 (2) Introducing the new component with low dielectric constant by the processing and forming method, such as blending with fluorographene 14–17 or other fillers with low dielectric constant like covalent organic frameworks (COFs) 18 and polyhedral oligomeric silsesquioxane (POSS); 19–25 (3) Fabricating air pore structure in the film due to the dielectric constant of air is only 1, 26 which is the simplest and most versatile method. Wang et al used the delayed phase transformation method to introduce pores to poly (aryl ether nitrile) (PEN) matrix and obtained ultra‐low dielectric constant PEN foam 2 .…”