Ramp rate effect on polyimide film properties and morphology

The stress in films of semirigid and rigid polyimides (PIs) on silicon (Si) substrate has been measured in situ during curing using a newly modified bending beam apparatus. By using the apparatus, the onset of residual stress in the initially solvent-rich films has also been investigated. The stress characteristics of the PI films are strongly ramp rate dependent. Different ramp rates result in markedly different stress patterns, thermo-mechanical properties, and film morphologies. The residual stress at room temperature after curing is scattered around 23–31 MPa for the films of pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA). For pyromellitic dianhydride-p-phenylenediamine (PMDA-PDA), it systematically increases from ?6 to 28 MPa for ramp rate increasing from 0.5 to 10°C/min. The residual stress is very low in the slowly cured PMDA-PDA films. However, these films have gone through a very high-stress transient state during curing. The maximum transient stress is comparatively higher in the films of PMDA-PDA than in PMDA-ODA. Slowly cured PMDA-PDA films exhibit high structural ordering, high in-plane anisotropy, and low coefficient of thermal expansion. ©1995 John Wiley & Sons, Inc.     

A study of solvent diffusion in thin polyimide films using laser interferometry

Using laser interferometry, we have determined in situ the thickness increase with time of thin supported polyimide films (4–8 μm in initial thickness) immersed in n-methyl-2-pyrrolidone (NMP) as a function of NMP temperature (22–120°C). Similar experiments were also performed in dimethyl sulfoxide (DMSO) at 22°C with polyimide films of 4.1 μm in thickness. For NMP, the equilibrium fractional thickness increase (about 20%) is independent of initial polyimide thickness and temperature. The time scale for reaching equilibrium sharply decreases with temperature from 2–3 days at 22°C to 30–60 min at 120°C. Compared with NMP, the rate of DMSO sorption is considerably faster, reaching equilibrium swelling of about 28% in about 5 h at 22°C. To describe the transport process, we applied a phenomenological model proposed by Astarita and Sarti¹ but reformulated in polymer fixed frame to enable straightforward comparison with the thickness data. Our analysis indicated that the transport of NMP is best described as anomalous, that is, intermediate between diffusion controlled and case II transport. The effective diffusion coefficient D_eff and the front velocity U₀ at 22°C were found to be 3–6 × 10^?12 cm²/s and 8 × 10^?9 cm/s, respectively. Our front velocity is in good accord with the value of 6 × 10^?9 cm/s obtained for a similar polyimide based on gravimetric measurements.² Both D_eff and U₀ show an activation energy of ～56 kJ/mol. For DMSO, however, the transport is clearly case II. The front velocity at 22°C was found to be about 6 × 10^?8 cm/s, which is about four times that obtained by Rutherford back-scattering spectrometry.³     

Residual stress and optical properties of fully rod-like poly(p-phenylene pyromellitimide) in thin films: Effects of soft-bake and thermal imidization history

A soluble poly(amic acid) precursor solution of fully rod-like poly(p-phenylene pyromellitimide) (PMDA-PDA) was spin cast on silicon substrates, followed by soft bake at 80–185°C and subsequent thermal imidization at various conditions over 185–400°C in nitrogen atmosphere to be converted to the polyimide in films. Residual stress generated at the interface was measured in situ during imidization. In addition, the imidized films were characterized in the aspect of polymer chain orientation and ordering by prism coupling and X-ray diffraction. The soft-baked precursor film revealed a residual stress of 16–28 MPa at room temperature, depending on the soft bake condition: higher temperature and longer time in the soft bake gave higher residual stress. The stress variation in the soft-baked precursor film was not significantly reflected in the final stress in the resultant polyimide film. However, the residual stress in the polyimide film varied sensitively with variations in imidization process parameters, such as imidization temperature, imidization steps, heating rate, and film thickness. The polyimide film exhibited a wide range of residual stress, −7 MPa to 8 MPa at room temperature, depending on the imidization condition. Both rapid imidization and low-temperature imidization generated high stress in the tension mode in the polyimide film, whereas slow imidization as well as high temperature imidization gave high stress in the compression mode. Thus, a moderate imidization condition, a single- or two-step imidization at 300°C for 2 h with a heating rate of < 10 K/min was proposed to give a relatively low stress in the polyimide film of < 10 μm thickness. However, once a precursor film was thermally imidized at a chosen process condition, the residual stress–temperature profile was insensitive to variations in the cooling process. All the films imidized were optically anisotropic, regardless of the imidization history, indicating that rod-like PMDA-PDA polyimide chains were preferentially aligned in the film plane. However, its degree of in-plane chain orientation varied on the imidization history. It is directly correlated to the residual stress in the film, which is an in-plane characteristic. For films with residual stress in the tension mode, higher stress films exhibited lower out-of-plane birefringence, that is, lower in-plane chain orienta-tion. In contrast, in the compression mode, higher stress films showed higher in-plane chain orientation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1261–1273, 1998     

Stress in polyimide coatings

The effect of film thickness on in-plane molecular orientation and stress in polyimide films prepared from pyromellitic dianhydride with 4,4′-oxydianline was investigated using a prism coupling technique to measure the refractive index. Film thickness was controlled by varying both solution concentration and spinning conditions. Birefringence, the difference between the in-plane and out-of-plane refractive indices, was used to characterize the in-plane molecular orientation. The observed birefringence is a combination of the birefringence resulting from molecular orientation and the birefringence induced by the residual stress present in the films. The birefringence decreases with increasing film thickness over the range of thicknesses studied (3–20 μm) indicating that the molecular orientation decreases with increasing film thickness. The in-plane coefficient of linear thermal expansion (CTE), controlled by the level of orientation in the film, increases from 18 to 32 × 10^?6/°C over the same thickness range. The birefringence of free-standing films was lower than that of adhered films due to the release of residual stress in the film once the film is removed from the substrate. The residual film stress arises primarily from the mismatch in CTEs between the polyimide film and the substrate to which the film is adhered. Thus, since the film anisotropy decreases with increasing thickness, the film stress increases with increasing thickness. Residual stress calculated by integrating the product of the film modulus and the CTE mismatch assuming temperature-dependent properties is comparable to experimentally measured film stress. Ignoring the temperature dependence of the film properties leads to an overestimation of stress. Moisture uptake was used to study the stress dependence of the optical properties. Moisture uptake increases both the in-plane and out-of-plane refractive indices by equal amounts in free-standing films due to an isotropic increase in the polarizability. In adhered films, an increase in moisture uptake leads to a decrease in the birefringence due to a swelling-induced decrease in the residual film stress. © 1994 John Wiley & Sons, Inc.     

Lithium intercalation in thin amorphous-silicon films

Electrochemical intercalation of lithium in thin films of amorphous hydrogenated silicon (a-Si:H), deposited at temperatures of 100 and 250°C on stainless-steel substrates, is studied. It is shown that the discharge capacity of films of identical thicknesses manufactured at a temperature of 250°C is greater than that for films produced at of 100°C. Dependence of the discharge capacity of the films manufactured at 250°C on their thickness is examined. It is established that an increase in the film thickness leads to acceleration of the decrease in the discharge capacity in the course of cycling. At a current density of 0.175 mA cm^?2, the discharge capacity of films 0.25 and 1.35 μm thick equals nearly 2 Ah g^?1 in a third cycle, whereas in a hundredth cycle it amounts to 1.10 and 0.37 Ah g^?1, respectively. The diffusion coefficient for lithium in the films is equal to ～10^-13 cm²s^?1.     

Swelling behavior of an aromatic polyimide

The swelling behavior of poly(N, N'-bisphenoxyphenylpyromellitimide) (PMDA-ODA) using dimethylsulfoxide DMSO and N-methylpyrollidinone NMP was investigated by gravimetric means. For PMDA-ODA samples imidized on a substrate, the weight uptake was found to depend linearly on time over a temperature range from 25 to 150°C. For a given temperature of imidization, the equilibrium swelling concentration was found to be independent of the temperature at which the swelling studies were performed. However, the rate of solvent uptake depended strongly on the swelling temperature, yielding an activation energy of about 50 kJ/mol. In general, increasing the initial imidization temperature caused a decrease in the rate of swelling but did not alter the equilibrium swelling concentration. This swelling behavior resembles Case II diffusion typically seen in glassy polymers with some noteworthy exceptions. In cases, where PMDA-ODA was imidized in a free-standing state, no swelling was observed. However, deformation of these isotropic specimens was found to induce substantial swelling.     

Effects of humidity,imidization history,and thickness on water sorption behavior of poly(p-phenylene biphenyltetracarboximide) films

Poly(p-phenylene biphenyltetracarboximide) films with various thicknesses were prepared from the poly(amic acid) precursor by thermal imidization at 230–400°C for 1–10 h under a nitrogen atmosphere. The water sorption in the films was measured at 25°C over 22–100% relative humidity using a Cahn microbalance as a function of film thickness and thermal imidization history. The water diffusion in all the films followed nearly Fickian process despite the morphological heterogeneity due to the ordered and less ordered phases. The diffusion coefficient and water uptake varied in 0.85 × 10^?10 ? 7.50 × 10^?10 cm²/s and 0.12–2.4 wt %, respectively, depending upon humidity, film thickness, and imidization history. Both diffusion coefficient and water uptake increased with increasing humidity, but decreased as imidization temperature and time increased. With increasing film thickness, the diffusion coefficient increased whereas the water uptake decreased. The water sorption behavior was interpreted with the consideration of morphological variations, such as polymer chain order, in-plane orientation, and intermolecular packing order due to the film thickness and imidization history. © 1995 John Wiley & Sons, Inc.     

Relationship between the functional group concentrations and the infrared reflection–absorbance of polyacrylonitrile films

The optical constants n and k of polyacrylonitrile (PAN) were determined in the infrared region 3100–700 cm^?1 by using theoretical calculations and experimental reflectance spectra. Tests of the validity of the results obtained showed excellent agreement between the measured and the predicted k values. One k value was determined experimentally (k = 0.6155 at V = 2285 cm^?1) and showed excellent agreement with that calculated theoretically (k = 0.6153). The p-polarized light was found to be more sensitive than the s-polarized light to the absorbance of PAN films at 77° incidence angle. This sensitivity increased rapidly with p-polarized light for film less than 0.5 μm thick. From the optical constants obtained for p-polarized light at 77° angle of incidence, the sensitivity of the infrared reflection-absorbance (IR-RA) measurements to changes in the functional group concentrations in PAN films was determined for film thicknesses in the region 0.01-10.0 μm. The IR-RA measurements of the ? C?N group and the skeletal mode were for a PAN film thickness of about 0.1 μm.     

Synthesis and Characterization of a Highly Soluble Aromatic Polyimide from 4,4′‐Methylenebis(2‐tert‐butylaniline)

4,4′‐Methylenebis(2‐tert‐butylaniline) was synthesized and reacted with pyromellitic dianhydride to produce a polyimide that showed excellent solubility in conventional organic solvents. Solutions of this polyimide could be cast into transparent, flexible and tough films. The number‐average molecular weight, as determined by means of gel permeation chromatography, was 8.9×10⁴ g/mol and the polydispersity index was 1.97. The glass transition temperature was found to be 217°C. The polyimide did not show appreciable decomposition up to 500°C under a nitrogen atmosphere.     

Polyimide containing internal acetylene units linked para to the aromatic ring

4,4′-Diaminodiphenylacetylene (p-intA) was reacted with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) in N-methyl-2-pyrrolidone (NMP) to give poly(amic acid) solution of moderate to high viscosity. Thermal imidization gave polyimide having acetylene units that are linked para to the aromatic connecting unit. Polyimide having acetylene units that are linked meta to the aromatic connecting unit also was prepared utilizing 3,3′-diaminodiphenylacetylene (m-intA) for comparison. The crosslinking behavior of the acetylene units was observed with DSC. Exotherm due to the crosslinking of the para-linked acetylene units appeared at ca. 340 to 380°C depending on the structure of polyimide, whereas meta-linked acetylene units appeared at lower temperature as 340–350°C. After thermal treatment at high temperature such as 350 or 400°C, the amount of the exotherm became smaller and finally disappeared on DSC, confirming the progress of crosslinking. Dynamic mechanical properties of the polyimide films show that glass transition temperature increased with higher heat treatment, also confirming the progress of crosslinking. Tensile properties of the polyimide films showed that rigid polyimide films consisting of p-intA with BPDA or PMDA have considerably higher modulus than those consisting of m-intA. Cold-drawing of the poly(amic acid) followed by imidization gave much higher modulus in the case of rigid polyimide. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2395–2402, 1997     

Polycarbazole Copolymers from 3-(4-Fluorobenzoyl)carbazole and 4,4′-Biphenol via Combined C-N and C-O Coupling Reactions with Activated Difluorides

3-(4-Fluorobenzoyl)carbazole was synthesized by a Friedel-Crafts reaction of carbazole with 4-fluorobenzoylchloride. ¹H-NMR and MALDI-TOF MS confirmed the structure and the purity. Copolymers of these NH/OH-containing monomers were prepared with 4, 4′-biphenol and bis(4-fluorophenyl)sulfone as comonomers by combined C-O and C-N coupling reactions with activated difluorides. These copolymers were soluble in N-methylpyrrolidinone (NMP), dimethylsulfoxide (DMSO), N,N-dimethylacetamide (DMAc) and dimethylformamide (DMF). The inherent viscosities of the copolymers in NMP solutions at 30°C were all around 0.8 dL/g. They could be easily cast into tough films from NMP solutions. The copolymers exhibited T_gs ranging from 238°C to 282°C. Thermal stabilities by TGA showed no weight loss below 400°C and the temperatures of 5% weight loss ranged from 535°C to 558°C. The homopolymer of 3-(4-fluorobenzoyl)carbazole was insoluble in common solvents and had a T_g of 332°C, and temperature of 5% weight loss of 560°C. UV-VIS absorption and fluorescence of the polymers are also presented.     

Diffusion energies of oxygen diffusing into polystyrene (PS)/poly (N‐isopropylacrylamide) composites

Diffusion coefficient of oxygen penetrating into polystyrene (PS) latex/poly (N‐isopropylacrylamide) (PNIPAM) microgel composite films were measured using Fluorescence technique. Three different (5, 15, and 40 wt%) PS content films were prepared from PS/PNIPAM mixtures. Diffusivity of PS/PNIPAM composite films were studied by diffusion measurements which were performed over the temperature range of 24–70°C. Pyrene was used as the fluorescent probe. The diffusion coefficients (D) of oxygen were determined using the Stern–Volmer fluorescence quenching method combined with Fickian transport and were computed as a function of temperature for each PS content film. The results showed that D values were strongly dependent on both temperature and PS content in the film. Diffusion energies were measured and found to be dependent on the composition of the composite films. Copyright © 2011 John Wiley & Sons, Ltd.     

Oxygen Diffusion into Polymer-Clay Composite Films as a Function of Clay Content and Temperature

Summary: A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene-clay composite films as a function of clay content and temperature. The composite films were prepared from a mixture of surfactant-free pyrene-labeled polystyrene latexes and modified Na-montmorillonite clay of various compositions at room temperature. Diffusion measurements were performed with films at room temperature for seven different clay contents (0, 5, 10, 20, 30, 50 and 60 wt.%). The diffusion coefficients of oxygen increased from 7.4 × 10⁻¹⁰ to 26.9 × 10⁻¹⁰ cm²s⁻¹ with increasing clay content. On the other hand, diffusion measurements were performed over a temperature range of 25–70 °C for 0, 5 and 20 wt.% clay content films. The calculated diffusion activation energies decreased from 2.44 to 0.44 kcal/mol with increasing clay content. No clay content and temperature effects were observed on quenching rate constant and mutual diffusion coefficient values. The results showed that the diffusion coefficients are strongly dependent on both the temperature and clay content in the film.     

Electrical,Mechanical, and Thermal Properties of Poly(4,4′-Cyclohexylidene Diphenylene-m-Benzene/Toluene-2,4-Disulfonate)

Abstract

The films of poly(4,4′-cyclohexylidene diphenylene-m-benzene disulfonate) (PSBB, 0.610 mm thick) and poly(4,4′-cyclohexylidene diphenylene-toluene-2,4-disulfonate) (PSBT, 0.537 mm thick) showed 8.23 ± 0.25 and 9.6 ± 0.245 kV, respectively, as the dielectric breakdown voltage (ac) in air at room temperature. The same films have 8.8 × 10¹¹ and 7.2 × 10¹⁴ ω°Cm volume resistivity. PSBB (40 μm thick) and PSBT (50 μm thick) films have tensile strengths of 1971 and 1677 kg/cm² and percent elongations of 1.3 and 1.2, respectively. The static hardnesses of PSBB (0.178 mm thick) and PSBT (0.190 mm thick) at three different loads (15–60 g) are 12.8–15.5 and 14.5–16.5 kg/mm², respectively. PSBB and PSBT are thermally stable up to about 355°C in an N₂ atmosphere and involve two-step degradation. DSC and DTA showed T _g at about 125–127 and 138–142°C, respectively, for PSBB and PSBT in N₂. PSBB and PSBT have comparable breakdown voltages and volume resistivity with some useful plastics whereas they have superior T _g and thermal stability with retention of excellent solubility in common solvents over polysulfonates without a cardo group. Thus, the cardo (cyclo-hexyl) group has enhanced thermal and mechanical properties with excellent solubility and easy processing.     

Preparation and characterization of branched and linear sulfonated poly(ether ketone sulfone) proton exchange membranes for fuel cell applications

Branched sulfonated poly(ether ketone sulfone)s (Br‐SPEKS) were prepared with bisphenol A, bis(4‐fluorophenyl)sulfone, 3,3′‐disodiumsulfonyl‐4,4′‐difluorobenzophenone, and THPE (1,1,1‐tris‐p‐hydroxyphenylethane), respectively, at 180 °C using potassium carbonate in NMP (N‐methylpyrrolidinone). THPE, as a branching agent, was used with 0.4 mol % of bisphenol A to synthesize branched copolymers. Copolymers containing 10–50 mol % disulfonated units were cast from dimethylsulfoxide solutions to form films. Linear sulfonated poly(ether ketone sulfone)s (SPEKS) were also synthesized without THPE. The films were converted from the salt to acid forms with dilute hydrochloric acid. A series of copolymers were studied by Fourier transform infrared, ¹H‐NMR spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. The ion‐exchange capacity (IEC), a measure of proton conductivity, was evaluated. The synthesized Br‐SPEKS and SPEKS membranes exhibit conductivities (25 °C) from 1.04 × 10^?3 to 4.32 × 10^?3 S/cm, water swell from 20.18 to 62.35%, IEC from 0.24 to 0.83 mequiv/g, and methanol diffusion coefficients from 3.2 × 10^?7 to 4.7 × 10^?7 cm²/S at 25 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1792–1799, 2008     

Free radical initiated low temperature crosslinking of phenylethynyl (PE) end‐capped oligomides

A relatively low‐temperature crosslinking method for phenylethynyl (PE) end‐capped oligomides was developed. PE end‐capped oligomides are typically cured into crosslinked polyimides at 370 °C for about 1 h. The addition of a low viscosity mixed‐solvent of N‐methylpyrrolidinone (NMP)/dimethyl ether of polyethylene glycol (M = 250 g/mol), NMP/DM‐PEG‐250, or NMP/polyethylene glycol (M = 400 g/mol), NMP/PEG‐400, as film forming medium for PE‐end‐capped oligomides was investigated. Fourier transform infrared spectroscopy and ¹³C NMR showed that the mixed solvent addition was effective for achieving low‐temperature crosslinking of the ethynyl end‐caps over the temperature range 200–250 °C. The low temperature crosslinking process was explained by thermolysis of the PEG molecules over this temperature range forming free radical species such as ～CH₂CH₂O· or ～CH₂CH₂^· which initiate cure of the ethynyl groups resulting in a cross linked polyimide membrane. The PEG solvents also provide a radical source for the degradation polymerization of the solvents to a water and NMP insoluble polymer, which formed a miscible blend with the crosslinked membrane. Glass transition temperature (differential scanning calorimetry) data and thermo gravimetric analysis data provide evidence for the miscible blend. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3950–3963, 2010.     

NLO‐active maleimide copolymers with ­high glass transition temperatures

We synthesized some novel rigid NLO‐active maleimide copolymers bearing DR‐1 moieties ( PMPD , PHSD and PHND ). All copolymers exhibited high T_g's (190～197 °C), good solubilities for common solvents and excellent film‐forming properties. Dependence of film thickness on the d₃₃ value for the poled copolymer films induced by corona poling was investigated and it was demonstrated that in less than thickness of 0.3 µm decrease of the thickness gives rise to remarkable increase in the d₃₃ value. The poled copolymer films exhibited large d₃₃ values (270 × 10^?9 esu (film thickness 0.13 µm) for PMPD , 290 × 10^?9 esu (0.12 µm) for PHSD and 350 × 10^?9 esu (0.08 µm) for PHND ) as well as large r₃₃ values (51.0 pmV^?1 for PMPD and 60.4 pmV^?1 for PHND ) which are significantly large compared to the value of LiNbO₃ (31 pmV^?1) as a typical EO material. The d₃₃ values of the poled copolymers were kept constant even after standing 1000h at 80 °C, although a small decrease was observed at an initial stage. Further, the d₃₃ values did not change up to ca. 123 °C upon heating at the rate of 10 °C/min in all cases. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis and properties of aliphatic-aromatic poly(amide-imide)s from sulfonyldianilines and N,N′-bis(ω-carboxyalkyl)pyromellitimides

Seven imide-containing dicarboxylic acids IIa-g were synthesized from pyromellitic dianhydride and amino acids of the formula HOOC—(CH₂)_m—NH₂, with m—1,2,3,4,5,10,11. These diacids were condensed directly with 3,3′- or 4,4′-sulfonyldianiline using triphenyl phosphite in N-methyl-2-pyrrolidone (NMP)-pyridine solution containing calcium chloride and lithium chloride. The resulting poly(amide-imide)s have moderate to high inherent viscosities ranging from 0.47 to 2.02 dL/g in dimethylacetamide. These polymers showed excellent solubility in polar solvents such as NMP, and most of them could be cast into transparent and tough films. Glass transition temperatures (T_gs) of these poly(amide-imide)s were recorded in the range 116–258°C and increased with decreasing number of methylene groups in the repeated unit. The polymers with longer aliphatic chains (e.g., m = 10 and 11) exhibited higher crystallinity, higher initial decomposition temperature, and lower solubility in polar solvents.     

Alkali‐treated semiconducting polypyrrole for infrared detection

A simple treatment of a polypyrrole (PPy) film with sodium hydroxide (NaOH) solutions reduces the conductivity (i.e., increased the resistance) and makes the film heat sensitive in the infrared (IR) spectrum with wavelength from 2.5 to 15.4 μm. The IR sensitivity increases with increasing treatment time in NaOH solutions and increasing exposed area to the radiation. The temperature coefficient of resistance, α, quantifying the sensitivity to IR, of the NaOH‐treated PPy is comparable with that of silicon and other conventional materials. The reduction and recovery of resistance due to IR on/off exposure exhibit a t^β dependence, where t is the time and β is determined to be around 0.5. This implies that the response of the material is controlled by diffusion of heat flux into and out of the sample. It is also observed that thermal ageing of the NaOH‐treated PPy film enhances the IR sensitivity. The sensing response of the treated films is observed beyond the thermal IR region to ultraviolet–visible wavelengths. Thus, the NaOH‐treated PPy appears to be a broadband sensing material. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Synthesis and properties of thermoplastic polyimides with ether and ketone moieties

A series of polyimides containing ether and ketone moieties were synthesized from 1,3‐bis(4‐fluorobenzoyl) benzene and several commercially available dianhydrides via a conventional two‐step polymerization. The inherent viscosities of Polyamide acids ranged from 0.46 to 0.73 dL/g. Thermal properties, mechanical properties, and thermalplasticity of the obtained polimide films were investigated by focusing on the chemical structures of their repeat units. These films were amorphous, flexible, and transparent. All films displayed low T_gs (184–225 °C) but also excellent thermal stability, the 5% weight loss temperature was up to 542 °C under nitrogen. The films showed outstanding mechanical properties with the modulus up to 3.0 GPa and the elongation at break in the range of 8–160%. The uniaxial stretching of PI‐a at high temperature was studied owing to its excellent flexibility. The PI‐a had an elongation at break up to 1600% at 245 °C and the uniaxially stretched film exhibited a much higher modulus (3.9 GPa) and strength (240 MPa) than undrawn film. The results indicated that PI‐a can potentially be used to prepare materials such as fiber, ultra‐thin film or ultra‐high modulus film. All the obtained films also demonstrated excellent thermoplasticity (drop of E′ at T_g > 10³) which made the polyimides more suitable for melt processing. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2878–2884, 2010