Xuemin Dai

Synthesis and properties of novel polyimide fibers containing phosphorus groups in the main chain

A series of polyamic acid copolymers (co-PAAs) containing phosphorous groups in the main chain were synthesized using different ratios of two diamines, i.e., bis(3-aminophenyl)methyl phosphine oxide (DAMPO) and 4,4′-oxydianiline (ODA), with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) by polycondensation in N,N′-dimethyacetamide (DMAc). The co-PAA solutions were spun into fibers by a dry-jet wet spinning process, and then polyimide copolymer (co-PI) fibers were obtained by thermal imidization. ATR-FTIR spectra and elemental analysis confirmed the chemical structure of PAA and PI fibers. The as-prepared PI fibers have smooth and dense surface as well as uniform diameter. Compared with the blank PI-0, the Tg values of co-PI fibers increased considerably with the increase in DAMPO content. TGA results indicated that the co-PI fibers possessed good thermal stability up to 510 °C and a residual char yield of up to 61% at 850 °C. All co-PI fibers exhibited excellent elongation, and their tensile strength and modulus can reach 0.9 GPa and 14.97 GPa when the molar ratio of DAMPO/ODA was 6/4 and the draw ratio was 3.0. The relationship between microstructure and mechanical property is also discussed.

AO-resistant properties of polyimide fibers containing phosphorous groups in main chains

A series of polyimide fibers containing phosphorus element derived from (3-aminophenyl) methyl phosphine oxide (DAMPO) diamine was exposed to an artificial atomic oxygen environment which simulated the space environment in low earth orbit (LEO). The mass loss, surface morphology, chemical composition, and mechanical properties of the fibers before and after atomic oxygen (AO) exposure were compared in detail with a blank sample. Results showed that the phosphor-containing fibers demonstrated lower mass change and less tensile strength reduction. SEM results showed that the fibers with phosphorous element had relatively dense surface after AO exposure. Meanwhile, XPS results indicated that a passivated phosphate layer, which could protect the following under-layer from attacking by AO, was formed on the surface of the fibers. These results indicated that the incorporation of diamine (DAMPO) into the main chains could protect the fibers for avoiding further erosion from AO exposure. Hence, the phosphor-containing PI fibers exhibits potential application in space fields.

Low-dielectric polyimide nanofoams derived from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride and 2,2′-bis(trifluoromethyl)benzidine

Low-dielectric polyimide (PI) nanofoams were prepared by introducing nanopores into the PI matrix containing fluorine groups. The nanopores were formed by thermolysis of the thermally labile content, namely, polyethylene glycol (PEG) oligomers, in air. The prepared PI nanofoams were characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and broadband dielectric spectroscopy. Results indicated that the PI nanofoams showed nanosized closed pores, excellent thermal stability, and a low dielectric constant of 2.12. The dielectric constant of the as-prepared nanofoams was stable within −150 °C to 150 °C. The thermal decomposition process of PEG in the PI matrix was designed and optimized to control the decomposition rate of PEG and the diffusion rate of the decomposition products of PEG. The dielectric constant of the nanofoams significantly decreased from 2.45 to 2.12 as the heating rate decreased from 5 °C min−1 to 1 °C min−1. The as-prepared PI nanofoams exhibited excellent properties and thus could be used in the microelectronics industry as a dielectric layer, multi-chip modules, or integrated circuit chips.

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.

Atomic oxygen resistance of polyimide fibers with phosphorus-containing side chains

A series of polyimide (PI) fibers were spun and exposed to atomic oxygen (AO). The PI fibers contained phosphorus in the macromolecular side chain, which was derived from DATPPO diamine. An AO exposure experiment was conducted in a ground-based AO-effect simulation facility. The changes in the surface morphologies and compositions of PI fibers before and after AO erosion were investigated by field emission scanning electron microscopy and X-ray photoelectron spectrometry (XPS). After AO exposure, the phosphorus-containing PI fibers exhibited a denser surface morphology compared with that of the pure PI fibers. XPS results indicated that phosphate species formed on the surfaces of phosphorus-containing PI fibers after AO exposure protected against further erosion. After AO erosion, the mass loss of phosphorus-containing PI fibers was lower than that of pure PI fibers. Moreover, at an AO fluence of 5.0 × 1020 atoms per cm2, the retention of tensile strength and Youngs modulus of phosphorus-containing PI fibers were 64.87% and 66.04%, respectively, which were higher than those of pure PI fibers. The results of the current study are crucial for understanding the relationship between polymer structure and AO-resistant properties of PI fibers to develop new materials with low-earth orbit applications.

Surface modification of high-performance polyimide fibres by using a silane coupling agent

ABSTRACT The silane coupling agent 3-aminopropyltriethoxysilane (KH-550) was used to modify the surface of two kinds of high-performance polyimide (PI) fibres (i.e., PI-1 and PI-2). The surface chemical composition, morphologies and roughness of modified PI fibres were characterised by XPS, SEM and AFM. Results showed that the elemental ratio between O and C, the surface oxygen concentration and the surface roughness increased with KH-550 concentration. However, the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) values of PI fibre/epoxy resin composites increased and then decreased with KH-550 concentration. When KH-550 concentration was increased to 4 wt%, the IFSS and ILSS values reached their maximum point. At this point, the IFSS values were found increase by 17.3% and 8.3% for PI-1 and PI-2, respectively, compared with their pristine state. Meanwhile, the ILSS values of PI-1- and PI-2-reinforced composites were found increase by 22.4% and 24.1%, respectively. Graphical Abstract GRAPHICAL ABSTRACT

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.