Aromatic Poly Amide-imide Research Articles

Relaxation processes in an aromatic polyamide-imide and composites on its basis with hydrosilicate nanoparticles

Features of the relaxation behavior of an aromatic polyamide-imide and a composite with nanotubes of magnesium silicate with the structure of chrysotile have been studied by dynamic mechanical analysis, dielectric spectroscopy, and differential scanning calorimetry. Two secondary relaxation (β1 and β2) transitions have been found, the activation energies of these processes have been determined, and the solvent effect on the cooperativeness degree has been studied. Changes in the value of the apparent activation energy of the β1-process caused by the subsequent heating of polymeric and composite samples have been analyzed according to the Starkweather procedure. It has been shown that, as the solvent is released from the polyamide-imide film, the polymer exhibits increasing local mobility, which are predetermined by the structure of the molecular unit. Using the GAMESS software, we have assumed the most probable dimer conformations that correspond to two repeating units of the polyamide-imide molecule.

Fracture toughness of polyimide films

Two aromatic polyimides and an aromatic polyamide-imide were tested in single-edge-notched tension. Fracture toughnesses, K c, normalized to 25 μm film thickness ranged from 1.65 to 5.4 MPa m 1 2 . LARC-TPI, a thermoplastic polyimide, showed evidence of crazing ahead of a growing crack whereas the other materials formed a shear yielded zone.

Initial evaluation of novel polyamide-imides and their copolymers as adhesives

Continued interest by the research community in thermally stable, tough, high temperature adhesives has resulted in the investigation by Langley Research Center of two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either 3,3'=DABA or 4,4'-DABA and BTDA. The two polymers were prepared with a monomer ratio of 0.75 DABP:0.25 DABA:1.00 BTDA. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) was the main criteria used to evaluate the polymers as adhesives. LSS of bonded Ti-6Al-4V was determined at room temperature (RT), 177, 204 and 232 C. The glass transition temperature and the type of bond failure were also determined. The best LSS values of the four adhesive systems investigated were obtained with the PAI copolymer identified in the report as LARC-TPI (25 percent 3,3'-DABA); however, it did not produce LSSs nearly as high as LARC-TPI. The poor flow properties observed appear to be due to a combination of high molecular weight and the increased interchain electronic interactions associated with the amide group.

全芳香族ポリアミドイミドからなる高弾性率繊維ならびにフィルム

N, N′-ビス (2-クロル-4-アミノフェニル) テレフタルアミドと無水ピロメリト酸からなる規則性ポリアミドイミドの繊維及び等方性フィルムをつくった. 繊維の場合. 前駆重合体であるポリアミド酸のNMP溶液を湿式紡糸し. ついで化学的あるいは熱的にイミド化させた. 化学環化系の引張特性は強度12.2g/d. 弾性率1340g/dであった. また. X線回折の結果から. このポリマーの繊維周期は約25.9Åと推定された. これは繰り返し単位長にほぼ相当する. また. フィルムは流延法で作成した. 弾性率は最高で2530kg/mm2に達した.

Mechanical properties of an aromatic polyamide-imide composite film reinforced with an aromatic polyamide fiber cloth at high temperature

An aromatic polyamide-imide (PAI) film was reinforced with a plain cloth of aromatic polyamide fiber (Du Pont, Kevlar 49). The mechanical properties of the composite film were investigated by examination of the temperature dependencies of tensile dynamic mechanical properties, stress relaxation, and tensile stress-strain behaviors. The softening temperature of the composite film was lower than that of a homogeneous PAI film. At a high temperature, Kevlar fibers may act as a thermal conductor and lower the softening point of the PAI composite. The mechanical properties of the composite film at a high temperature are mostly controlled by the PAI matrix.

Preparation of graphite film by pyrolysis of polymers

Pyrolysis of aromatic polymers up to 3000°C was studied in relation to the molecular structure and orientation. Poly(p-phenylene vinylene), PPV, was pyrolyzed to give highly oriented graphite in keeping film form. Raman spectrum analyses indicated that PPV was converted into pure graphite above 2750°C. The graphite film obtained showed 10 4 S/cm as it was and 10 5 S/cm by SO 3-doping, which are comparable to those of the highly oriented pyrolytic graphite (HOPG). X-ray diffraction analyses and scanning electron micrographs for the pyrolyzed products suggest that the biaxial stretching facilitates graphitization of PPV and orientation of the graphite plane. Aromatic polyimide was also converted into graphite and showed 10 4 S/cm after pyrolysis at 3000°C, while aromatic polyamideimide and polyamide showed 10 3 S/cm at most after pyrolysis at the temperature.

Elastic and tensile properties of aromatic polyamideimide composite films with aromatic polyamide fiber reinforcements having various textures and fiber orientations

Aromatic polyamideimide (PAI) films were reinforced with aromatic polyamide fiber (DuPont, Kevlar 49) as unidirectional composite (type I), bidirectional laminate composite (type II), and bidirectional cloth composite (type III). The elastic and tensile load-elongation properties of composite films at ambient temperature were investigated with respect to fiber orientation. The properties of the type I composite film are more anisotropic than those of other composite films. But, for the type I composite film, the most significant effect of the reinforcement fiber is observed at the fiber direction. With bidirectional reinforcement (type II and III) the anisotropy of the composite is reduced, but the strengths at the fiber directions are depressed markedly by the existence of the fibers of the other orientations.

Molecular aggregation of solid aromatic polymers. III. Small‐angle X‐ray scattering from aromatic polyamideimide film

AbstractMolecular aggregation in polytrimellitamideimide (PAI) was investigated by small‐angle x‐ray scattering (SAXS). PAI films annealed above the glass transition temperature show a scattering peak characteristic of two‐phase structure. A one‐dimensional model was used to analyze these SAXS curves. The more ordered phases are produced at higher annealing temperature. The average thickness of the ordered lamellae is comparable with the repeating length of the main chain. The relative difference of electron density between two phases is only a few percent, which shows that the two‐phase structure of PAI, like that of aromatic polyimide, differs essentially from that of ordinary crystalline polymers.

Thermal expansion of aromatic polyamideimide composite films reinforced with aromatic polyamide fibers

Aromatic polyamideimide (PAI) films were reinforced by aromatic polyamide fibers as a unidirectionally oriented composite (Type I) and bidirectionally oriented laminate composite (Type II). The thermal expansion of the composite films was investigated with respect to the direction of fiber orientation. The thermal expansion behavior was anisotropic in the unidirectionally reinforced composite films, and considerably isotropic in the bidirectionally reinforced composite film. The thermal expansion coefficients based on thermoelastic models are calculated and compared with experimental data.

Stress Relaxation and Thermal Expansion of Aromatic Polyamideimide-Aromatic Polyamide Fiber Composite Films

Aromatic Polyamideimide (PAI) films were reinforced by aromatic polyamide fiber as unidirectionally oriented composite (Type 1), bidirectionally oriented laminate composite (Type 2), and bidirectionally oriented cloth composite (Type 3). The stress relaxation and thermal expansion of the composite films were investigated with respect to direction of fiber orientation. The behavior of the unidirectionally oriented composite film was more anisotropic than that of other composite films. In the cloth composite film, the elastic behavior was isotropic. The thermal expansion behavior was isotropic in the laminate composite film. Thus the anisotropy of elasticity of the composite films does not always correspond to that of thermal expansion.

The degradation of an aromatic polyamideimide in an NO2 atmosphere

AbstractFilms of an aromatic polyamideimide showed a significant degradation in an NO2 atmosphere at 100 mm Hg at 50°C. The degradation was followed by the dynamic tensile measurements. In the curves of temperature dependence of dynamic loss modulus of degraded films, a separate mechanical absorption α′ peak appeared below the glass transition α peak. In the course of degradation, the α′ peak grew and shifted to lower temperature. On thermal treatment of degraded films, the α′ peak shifted to higher temperature and finally merged into the α peak. The formation of reacted surface layers by the diffusion of NO2 was confirmed by scraping off and by solvent extraction. Infrared spectroscopy showed that most amide linkages were destroyed by NO2. The gel permeation chromatography of extracted products showed that the low molecular products were occluded in degraded layers. The influence of these components caused the α′ absorption in dynamic loss curves.