co-PI Fibers Research Articles

Fabrication of high performance polyimide fibers by dry-jet wet spinning technology

High-performance co-polyimide (co-PI) fibers derived from 3,3`4,4`-biphenyldianhydride (BPDA), p-phenylenediamine (p-PDA) and 2-(4-aminophenyl)-5-amino-benzimidazole (BIA) were prepared via the wet spinning and dry-jet wet spinning method, respectively. The distinctions between wet spinning and dry-jet wet spinning processes on the structures and properties of co-PI fibers were systematically investigated. The co-PI fibers prepared by dry-jet wet spinning exhibited smoother surface morphology and higher mechanical properties than those of co-PI prepared by wet spinning. Wide-angle X-ray diffraction (WAXD) results showed that the co-PI fibers prepared by dry-jet wet spinning exhibited highly oriented structure along the fiber direction along with a low degree of lateral packing order in the transverse direction. Small-angle X-ray scattering (SAXS) revealed that the radius, length, misorientation and internal surface roughness of the microvoids in the co-PI fibers prepared by the dry-jet wet spinning are lower than those in co-PI fibers prepared by wet spinning. Moreover, the effect of air layer height, as well as the heat treatment on the structure and properties of fibers during the dry-jet wet spinning process, was also studied. The tensile strength and modulus of co-PI fibers prepared by dry-jet wet spinning reached 2.72 GPa and 114.29 GPa, respectively, with an air layer height of 10 mm and a heat stretching temperature of 440°C.

Preparation and properties of high-performance polyimide copolymer fibers containing rigid pyrimidine and benzoxazole moieties with hydrogen bonding

The utilization of 5-amino-2-(2′-hydroxy-4′-aminophenyl)-benzoxazole (HBOA) as third monomer was beneficial for the introduction of OH-type H-bonding into polyimide (PI) matrix through the copolymerization with 2,5-bis(4-aminophenyl)pyrimidine (PRM) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). And high-performance PI fibers were successfully fabricated via the dry-jet wet spinning process. The FTIR spectra confirmed that the strong interactions of intramolecular and intermolecular H-bonding existed simultaneously in PI fibers. Moreover, the glass transition temperatures (Tg) of all fibers were within 276–318 °C, and the temperatures at 5% weight loss (T5%) ranged from 574 °C to 604 °C, revealing the remarkable thermal stability of PI fibers. The two-dimensional wide-angle X-ray diffraction (2D WAXD) results illustrated a U-shaped change in the crystallinity (from 32.1% to 12.2% until 33.4%) of PI fibers with increasing HBOA content, which was also reflected in the density variation of fibers. The two-dimensional small-angle X-ray scattering (2D SAXS) patterns demonstrated that the micro-defects in all co-PI fibers profitably decreased in comparison with those in homo-PI fibers. Furthermore, the orientation factor of fibers presented an improvement from 0.843 to 0.899 after incorporating HBOA moiety. When the molar ratio of PRM/HBOA was 7/3, the co-PI fiber exhibited optimum mechanical properties with tensile strength and modulus as high as 4.15 GPa and 125.93 GPa, respectively. Interestingly, the variation in fiber orientation was in line with the same trend as that of mechanical properties of PI fibers, indicating orientation was also a crucial factor to improve the mechanical properties. The relationship between structure and mechanical property was also investigated.

Structure-property relationship of low dielectric constant polyimide fibers containing fluorine groups

A series of copolyimide (co-PI) fibers with low dielectric constants and excellent comprehensive properties have been successfully prepared via a two-step wet-spinning method by incorporating 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) into rigid polymer backbones of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (p-PDA). The dielectric constant of PI fibers were substantially reduced from 3.0 to 2.48 at the frequency of 10 GHz after the introduction of trifluoromethyl (-CF3) groups. Meanwhile, the prepared PI fibers exhibited high thermal stability as well as excellent mechanical properties. The co-PI fibers possessed the optimum tensile strength of 1.4 GPa and modulus of 83.3 GPa at the p-PDA/TFMB molar ratio of 7/3. The 5% weight loss temperature in nitrogen ranged from 523 to 558 °C, and the glass transition temperature decreased from 372 °C to 295 °C with increasing TFMB contents. Both experimental and molecular simulations method were adopted to discuss the influence of fluorine group on the aggregation structure and properties of PI fibers, suggesting that the improved free volume were the crucial factor responsible for low dielectric constant. The molecular ordered degree and orientation degree of co-PI fibers decreased firstly and further increased with increasing TMFB content, which is due to the combined effects of large free volume of trifluoromethyl and polymer regularity variation caused by copolymerization.

Fabrication and properties of polyimide copolymer fibers containing pyrimidine and amide units

Polyimide (PI) fibers containing pyrimidine and amide moieties were fabricated by the copolymerization of 2,5-bis(4-aminophenyl)pyrimidine (PRM) and 4,4′-diaminobenzanilide (DABA) with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) via a two-step method. The effects of chemical structure of PI fibers, i.e., various molar ratios of PRM/DABA, on their thermal property, crystallinity, orientation factor, microvoid defects, and mechanical property, were investigated in detail. The glass transition temperatures (Tg) of all PI fibers ranged from 282 to 310 °C, and the temperatures at 5% weight loss (T5%) under N2 and air atmosphere were respectively within 548–584 °C and 482–540 °C, demonstrating the excellent thermal stability and thermal oxidation stability of all fibers. The wide-angle X-ray diffraction data illustrated that the co-PI fibers had lower crystallinity than the homo-PI fibers due to a marked decrease in molecular order packing by copolymerization. However, the co-PI fibers possessed higher degrees of orientation relative to the homo-PI fibers. In particular, the co-PI fiber with PRM/DABA = 5/5 showed the highest orientation factor, fc = 0.872. Moreover, the small-angle X-ray scattering results, i.e., decrease in microvoid size, revealed that DABA incorporation helps to reduce the defects in PI fibers. When the PRM/DABA molar ratio was 5/5, the co-PI fiber possessed an optimal tensile strength and initial modulus of 3.43 and 136.92 GPa, respectively.

Microstructure evolution and properties of polyimide fibers containing trifluoromethyl units

A series of copolyimide (co-PI) fibers containing trifluoromethyl units were successfully obtained on the molecular design of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, p-phenylenediamine, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP) via a widely utilized two-step wet-spinning method. Significant variations on the microstructures and properties of the resulting co-PI fibers were observed after the incorporation of HFBAPP moieties. The tensile strength and initial modulus of the fibers decreased from 0.70 GPa to 0.38 GPa and from 69.63 GPa to 9.60 GPa, respectively. However, the dielectric permittivity decreased from 3.62 to 2.85 in the frequency of 10 MHz as a result of the incorporation of trifluoromethyl units. Two-dimensional wide-angle X-ray diffraction showed that the fibers exhibited highly oriented molecular alignments along the fiber direction and low lateral packing degree in the transverse direction. In addition, the co-PI fibers possessed excellent thermal–oxidative stabilities with the 5% weight loss temperature ranging from 532°C to 552°C under nitrogen atmosphere and the glass transition temperature ranging from 312°C to 330°C.

Preparation and Properties of High-performance Polyimide Copolymer Fibers Derived from 5-Amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole

A series of polyamic acid copolymers (co-PAAs) with para-hydroxyl groups was synthesized using two diamine monomers, namely p-phenylenediamine (p-PDA) and 5-amino-2-(2-hydroxy-5-aminobenzene)-benzoxazole (m-pHBOA), of different molar ratios through copolymerization with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) in N,N-dimethyacetamine (DMAc). The co-PAA solutions were used to fabricate fibers by dry-jet wet spinning, and thermal imidization was conducted to obtain polyimide copolymer (co-PI) fibers. The effects of the m-pHBOA moiety on molecular packing and physical properties of the prepared fibers were investigated. Fourier transform infrared (FTIR) spectroscopic results confirmed that intra/intermolecular hydrogen bonds originated from the hydroxyl group and the nitrogen atom of the benzoxazole group and/or the hydroxyl group and the oxygen atom of the carbonyl group of cyclic imide. As-prepared PI fibers displayed homogenous and smooth surface and uniform diameter. The glass transition temperatures (Tgs) of PI fibers were within 311−337 °C. The polyimide fibers showed 5% weight loss temperature (T5%) at above 510 °C in air. Two-dimensional wide-angle X-ray diffraction (WXRD) patterns indicated that the homo-PI and co-PI fibers presented regularly arranged polymer chains along the fiber axial direction. The ordered molecular packing along the transversal direction was destroyed by introducing the m-pHBOA moiety. Moreover, the crystallinity and orientation factors increased with increasing draw ratio. Small-angle X-ray scattering (SAXS) results showed that it is beneficial to reduce defects in the fibers by increasing the draw ratio. The resultant PI fibers exhibited excellent mechanical properties with fracture strength and initial modulus of 2.48 and 89.73 GPa, respectively, when the molar ratio of p-PDA/m-pHBOA was 5/5 and the draw ratio was 3.0.

Synthesis and AO Resistant Properties of Novel Polyimide Fibers Containing Phenylphosphine Oxide Groups in Main Chain

A series of co-polyimide (PI) fibers containing phenylphosphine oxide (PPO) group were synthesized by incorporating the bis(4-aminophenoxy) phenyl phosphine oxide (DAPOPPO) monomer into the PI molecular chain followed by dry-jet wet spinning. The effects of DAPOPPO molar content on the atomic oxygen (AO) resistance of the fibers were investigated systematically. When the AO fluence increased from 0 atoms·cm−2 to 3.2 × 1020 atoms·cm−2, the mass loss of the fibers showed the dependence on DAPOPPO molar content in co-PI fibers. The PI fiber containing 40% DAPOPPO showed lower mass loss compared to those containing 0% and 20% DAPOPPO. At higher AO fluence, the higher DAPOPPO content gave rise to dense carpet-like surface of fibers. XPS results indicated that the passivated phosphate layer was deposited on the fiber surface when exposed to AO, which effectively prevented fiber from AO erosion. With the DAPOPPO content increasing from 0% to 40%, the retentions of tensile strength and initial modulus for the fibers exhibited obvious growth from 44% to 68%, and 59% to 70%, after AO exposure with the fluence of 3.2 × 1020 atoms·cm−2. The excellent AO resistance benefits the fibers for application in low Earth orbit as flexible construction components.

High-performance polyimide copolymer fibers derived from 5-anino-2-(2-hydroxy-4-aminobenzene)-benzoxazole: Preparation, structure and properties

A series of high-performance polyimide copolymer (co-PI) fibers containing phenylenebenzoxazole moiety with one hydroxyl group are synthesized based on the copolymerization of 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) with two diamine monomers, namely, p-phenylenediamine (p-PDA) and 5-anino-2-(2-hydroxy-4-aminobenzene)-benzoxazole (p-mHBOA), through a two-step method. The molar ratio of p-PDA/p-mHBOA varies from 10/0 to 0/10. Influences of the p-mHBOA moieties on the thermal stability, crystal structure, crystal orientation, microvoid morphology, and mechanical properties are systemically investigated. Fourier transform infrared results confirm that intra/inter molecular hydrogen bonds come from the OH group and nitrogen atom of the benzoxazole group and/or OH group and the oxygen atom of the carbonyl group of cyclic imide. The glass transition temperatures (Tgs) of co-PI fibers are in the range of 290 °C–325 °C. The prepared fibers show excellent thermal stabilities, and their T5% is within 528 °C–542 °C in air. Two-dimensional wide-angle X-ray diffraction spectra indicate that homo-PI and co-PI fibers present a regularly arranged polymer chains along the fiber axial direction. Moreover, the ordered molecular packing along the transversal direction of fibers is destroyed by the copolymerization. Small-angle X-ray scattering results show that co-PI fibers with optimal mechanical properties exhibit the shortest average length (L) and the smallest radius (R¯) of microvoids. When the p-mHBOA/p-PDA molar ratio is 5/5, the fracture strength and initial modulus can reach approximately 30.31 cN/dtex (4.40 GPa) and 894.88 cN/dtex (129.8 GPa), respectively. The relationship between structure and mechanical properties is also discussed.

High-performance polyimide fibers derived from wholly rigid-rod monomers

Insufficient mechanical properties are one of the major obstacles for the wide application of polyimide (PI) fibers, especially utilized as reinforcement in structural composites. In this work, the copolymerization of two rigid-rod diamines, 2,5-bis(4-aminophenyl)-pyrimidine (PRM) and p-phenylenediamine (PPD), with the 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) was developed to fabricate PI fibers with high strength and high modulus. The effects of chemical structure (diamine molar ratio) on the molecular packing behavior, micromorphology as well as properties of the resulting co-PI fibers have been investigated in detail. Wide-angle X-ray diffraction spectra showed that co-PI fibers exhibited higher oriented structures with lower lateral packing order degrees in relative to both homo-BPDA/PRM and homo-BPDA/PPD PI fibers, and the Hermans’ orientation degrees reached 0.97 for the two samples with PRM/PPD molar ratio of 5/5 and 4/6. Small-angle X-ray scattering (2D SAXS) patterns indicated that the co-PI fiber with the PRM molar content of 50% showed the densest inner structure. Accordingly, this co-PI fiber presented a higher mechanical performance (tensile strength of 3.11 GPa and modulus of 144.2 GPa) as compared to those PI fibers reported previously. Meanwhile, these wholly rigid-rod PI fibers exhibited excellent thermal stabilities with the 5 and 10% weight loss temperatures ranging from 548 to 565 °C and from 572 to 589 °C, respectively. The prominent comprehensive properties make these PI fibers strong candidates for the future fiber-reinforced polymer composites.

Synthesis of organosoluble copolyimide and preparation of fibers by dry-spinning process on a large scale

An organosoluble copolyimide (co-PI) was synthesized from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 1,4-bis-(4-aimino-2-triflupromethyl-phenoxy)-benzene ( p-6FAPB), and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) via the one-step polymerization using N-methyl-2-pyrrolidone (NMP) as the solvent, and high-performance co-PI fibers were directly prepared by the dry-spinning process on a large scale. Scanning electron microscopic images show that all formulations of as-spun fibers exhibit elliptical cross sections as well as dense morphologies. The structural evolution of the co-PI fiber induced by the high rolling speed and post-heat-drawing treatment was studied by means of thermogravimetric analysis, dynamic thermomechanical analysis, and two-dimensional wide-angle X-ray diffraction (2D WAXD). With increasing rolling speeds, glass transition temperatures ( Tgs) and thermal stabilities of as-spun fibers slightly decrease, which may be resulted from the disentanglement of entangled molecular chains under the large deformation and high-temperature heating atmosphere in the spinning column. 2D WAXD data indicate that both increasing rolling speeds and post-heat-drawing treatment are beneficial for getting a highly ordered structure along the meridian direction of the fibers. The fibers treated at 430°C exhibit outstanding mechanical properties, and the tensile strength and modulus reach 1.44 GPa and 48.69 GPa, respectively, at a drawing ratio of 2.8.

Fabrication and characterization of co-polyimide fibers containing pyrimidine units

A series of co-polyimides (co-PIs) containing pyrimidine rings were synthesized by reacting the self-synthesized diamine 2,5-bis(4-aminophenyl)-pyrimidine (PRM) with commercial 4,4’-diaminodiphenyl ether (ODA) and aromatic 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). A series of co-PI fibers were produced using a two-step wet-spinning method, including extrusion, coagulation, washing, drying, thermal imidization and hot-drawing processes. Orientation structures of the precursor co-PAA fibers formed in the wet-spinning process, and their effects on the thermomechanical properties of the as-spun co-PI fibers were discussed. An interesting phenomenon has been found that glass transition temperatures (T gs) of as-spun co-PI fibers decreased with increasing orientation factors, which was explained based on some previous works. Two-dimensional wide-angle X-ray diffraction spectra of the final co-PI fibers showed that samples with higher PRM contents show highly oriented and well-ordered crystalline structures, which account for the enhanced mechanical properties when incorporating PRM moieties. The co-PI fiber with the PRM/ODA molar ratio of 6/4 showed an optimum tensile strength and modulus of 3.1 and 90 GPa, respectively, showing a great potential in light advanced composites.

Synthesis and properties of novel polyimide fibers containing phosphorus groups in the side chain (DATPPO)

A series of polyamic acid copolymers (co-PAAs) containing phosphorous groups in the side chains were synthesized from [2,5-bis(4-aminophenoxy) phenyl] diphenylphosphine oxide (DATPPO) and 4,4′-oxydianiline (ODA) with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) through the polycondensation in N,N′-dimethyacetamide (DMAc). The co-PAA solutions were spun into fibers by a dry-jet wet spinning process followed by thermal imidization to obtain co-polyimide (co-PI) fibers. FTIR spectra and elemental analysis confirmed the chemical structure of PI fibers. SEM results indicated that the resulting PI fibers had a smooth and dense surface, a uniform and circle-shape diameter. The thermogravimetric measurements showed that with the increase of DATPPO content, the resulting PI fibers possessed high decomposition temperature and residual char yield, indicating that the PI fibers had good thermal stability. The corresponding limiting oxygen index (LOI) values from the experiment results showed that the co-PI fibers possessed good flame-retardant property. Furthermore, the mechanical properties of the co-PI fibers were investigated systematically. When the DATPPO content increased, the tensile strength and initial modulus of the co-PI fibers decreased. However, the mechanical properties were improved by increasing the draw ratio of the fibers. When the draw ratio was up to 2.5, the tensile strength and initial modulus of the co-PI fibers reached up to 0.64 and 10.02 GPa, respectively. The WAXD results showed that the order degree of amorphous matter increased with increased stretching. In addition, the SAXS results displayed that valuably drawing the fibers could eliminate the voids inside and lead to better mechanical property. WAXD revealed that the orientation of the amorphous polymer influenced the mechanical properties of the fibers.

Preparation of high-performance polyimide fibers containing benzimidazole and benzoxazole units

A series of aromatic copolyimide (co-PI) fibers containing benzimidazole and benzoxazole were prepared by introducing 5-amino-2-(4-aminobenzene)benzoxazole (BOA) and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) into the rigid 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (p-PDA) backbone via a typical two-step wet-spinning method. The incorporated BOA and BIA moieties in the polymer chains resulted in significant changes on the comprehensive performances of the resulting PI fibers. The optimum tensile strength was 2.26 GPa with the BIA/BOA molar ratio of 3/1, whereas the optimum initial modulus was 145.0 GPa with the BIA/BOA molar ratio of 1/3. The drastically improved mechanical properties were originated from the hydrogen-bonding intermolecular interactions by BIA moieties and high molecular orientation by BOA moieties. FT-IR results confirmed the presence of hydrogen-bonding interaction in the fibers with high imidization degree. Two-dimensional wide-angle X-ray diffraction (2D WAXD) indicated the existence of highly oriented structures along the fiber axial direction, while this feature varied with different diamine ratios. SEM observations showed that the fibers were obtained with homogeneous and uniform structures at various diamine ratios. Meanwhile, the co-PI fibers exhibited excellent thermal properties with 5 % weight loss temperature ranging from 563 to 570 °C in nitrogen and glass transition temperature ranging from 308 to 321 °C.

Enhanced mechanical and hydrophobic properties of polyimide fibers containing benzimidazole and benzoxazole units

A series of rigid-rod co-polyimides (co-PI) containing benzimidazole and benzoxazole moieties were synthesized by the reaction of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 5-amino-2-(4-aminobenzene)benzoxazole (BOA) with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). The corresponding co-PI fibers with various diamine ratios were prepared by the two-step wet-spinning process. The small chemical structure difference between benzimidazole and benzoxazole moieties leads to unexpected great changes on the aggregation structures and properties of the obtained fibers. The two-dimensional wide-angle X-ray diffraction (WAXD) spectra imply that the co-PI fibers containing more than 70% molar ratio of BIA show better-defined ordered crystal structures, while for those samples with more BOA contents, a new ordered lateral packing occurs. Meanwhile, the equatorial scattering streaks in the small-angle X-ray scattering (SAXS) patterns for the co-PI fibers suggest the presence of microvoids, whose sizes were evaluated by means of Guinier and Ruland’s method. The optimum tensile strength and modulus of co-PI fibers are as high as 1.74 and 74.4GPa, respectively, at the BIA/BOA molar ratio of 7/3. Besides, the co-PI fibers exhibit excellent thermal and thermo-oxidative stabilities due to the rigid molecular chains. The introduction of BOA units in the polymer backbones have apparently improved the hydrophobic properties of PI fibers.

Structures and properties of polyimide fibers containing ether units

Copolyimide (co-PI) fibers containing 4,4′-oxydiphthalic anhydride (ODPA) moiety into the 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine backbone were prepared via a two-step wet-spinning method. The processability and mechanical properties were improved significantly after the incorporation of ODPA, and the fibers exhibited an optimum tensile strength of 10.94 cN dtex−1 and modulus of 470.52 cN dtex−1 with elongation of 2.75 % at a BPDA/ODPA molar ratio of 7/3. Two-dimensional wide angle X-ray diffraction indicated that highly oriented structures and ordered molecular packing regions were formed in the fibers. Two-dimensional small angle X-ray scattering revealed that the incorporation of ODPA resulted in the reduction in radius, length, misorientation, and internal surface roughness of the microvoids in the fibers simultaneously, which was supposed to be mainly dominated for the drastically improved mechanical properties of PI fibers. Moreover, the co-PI fibers exhibited excellent thermal and thermal-oxidative stability, and the 5 % weight loss temperature was above 572 and 535 °C under nitrogen and air, respectively.

Synthesis of organ-soluble copolyimides by one-step polymerization and fabrication of high performance fibers

A series of organ-soluble copolyimides (co-PIs) were synthesized from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 2,2′-bis(trifluoromethyl)-4, 4′-diaminobiphenyl (TFMB), and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) via a one-step polymerization in N-methyl-2-pyrrolidone (NMP). The polyimide solutions were used to fabricate as-spun polyimide fiber by a wet-spinning process. SEM images of the round cross-section of the fibers indicated that a homogeneous and dense fibrous structure was produced in the coagulation bath of H2O/NMP = 90/10 (v/v) and many microfibrils appeared on the surface. The drawn fibers exhibit excellent mechanical properties, and the strength and modulus of BTDA/TFMB/BIA co-PI fibers (TFMB/BIA = 50/50) reached 2.25 and 102 GPa with a draw ratio of 3.0. The 5 % weight loss temperature of the co-PI fibers in thermogravimetric analysis spectra achieved 548–563 °C in an air atmosphere. The glass transition temperatures were found to be between 340 and 366 °C according to the DMA results. Annealed BTDA/TFMB/BIA co-PI fibers displayed distinct wide-angle X-ray patterns, and crystallinity and crystal orientation with various draw ratios were observed.

High-performance copolyimide fibers containing quinazolinone moiety: Preparation, structure and properties

Copolyimide (co-PI) fibers with superior mechanical properties and high thermal stability were developed via a two-step polymerization/imidization process based on a new design of introducing an aromatic heterocyclic diamine monomer, 2-(4-aminophenyl)-6-amino-4(3H)-quinazolinone (AAQ) into rigid homopolyimide backbones of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (p-PDA). Effects of the incorporated AAQ moieties on the micro-structure and properties of the prepared fibers were investigated. Fourier transform infrared (FTIR) results indicated that hydrogen bonding is formed between the AAQ and cyclic imide units that effectively strengthens the intermolecular interactions. This has been considered to be the key factor responsible for the significantly enhanced mechanical properties of the co-PI fibers. Two-dimensional wide angle X-ray diffraction (2D WAXD) spectra showed that the co-PI fibers are highly oriented with well-ordered 2D structures along both the fiber and transverse directions. The co-PI fibers reached the optimum tensile strength and modulus of 2.8 GPa and 115 GPa, respectively, at the AAQ/p-PDA molar ratio of 5/5. The fiber also exhibited high thermal stability, with a 5%-weight-loss temperature of 599 °C under N2 and 564 °C in air.

Fabrication of high-performance copolyimide fibers from 3,3',4,4'-biphenyltetracarboxylic dianhydride, p-phenylenediamine and 2-(4-aminophenyl)-6-amino-4(3H)-quinazolinone

High-performance copolyimide (co-PI) fibers synthesized by 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), p-Phenylenediamine (p-PDA) and 2-(4-aminophenyl)-6-amino-4(3H)-quinazolinone (AAQ) were prepared via a two-step spinning technology. The influences of the thermal treatment temperatures on the structure, and mechanical and thermal properties of the co-PI fibers were studied. The co-PI fibers with excellent mechanical and thermal properties were obtained by heating the co-PAA fibers under a drawing ratio of 1.05 at 240°C and subsequently at 390°C. The tensile strength and modulus reach 2.6GPa and 112.3GPa, respectively. The 5%-weight-loss temperatures of the co-PI fibers under nitrogen and air achieve 611°C and 565°C, respectively, and the glass transition temperature is over 400°C.