Characterization of alicyclic polyimides based on cyclobutane ring dianhydride and aromatic diamine

Films of alicyclic polyamic acid and polyimide containing cyclobutane ring in dianhydride moiety and aromatic ring with p- or m-linkages in diamine moiety were characterized by infrared (IR) spectroscopy, dynamic viscoelasticity, differential-scanning calorimetry (DSC), density, and wide-angle X-ray diffraction analyses. Partially and fully imidized polyimides were obtained by varying the imidization temperature, e.g., 150°C, 250°C, and 350°C. It was found from the results of IR spectra, dynamic viscoelasticity, and DSC measurements that the imidization of alicyclic polyamic acid was reduced at about 150°C and needed a higher imidization temperature than aromatic polyamic acid. Alicyclic polyimide with m-linkage in the diamine moiety had a higher density and a much more ordered structure than with p-linkage. © 1994 John Wiley & Sons, Inc.     

Studies of polyimide/copper interface and its improvement by a two-component primer

The inhibition of the imidization of polyamic acid, a precursor of polyimide, in the presence of Cu, was confirmed by the incorporation of Cu²⁺ ions in polyamic acid films. It was found that the imidization reaction was incomplete below 300°C but decomposition took place when heating above 300°C. Pretreating the Cu surface with a two-component primer solution containing polybenzimidazole and 2-mercaptobenzimidazole can make the imidization proceed without retardation and avoid the decomposition above 300°C. By choosing appropriate surface treatment systems, one can achieve the improvement of adhesion between PI and Cu substrate.     

Polyimide foams with ultralow dielectric constants

To explore ultralow dielectric constant polyimide, the crosslinked polyimide foams (PIFs) were prepared from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA), and 2,4,6‐triaminopyrimidine (TAP) via a poly(ester–amine salt) (PEAS) process. FTIR measurements indicated that TAP did not yield a negative effect on imidization of PEAS precursors. SEM measurement revealed the homogeneous cell structure. Through using TAP as a crosslinking monomer, the mechanical properties of PIFs could be improved in comparison with uncrosslinked BTDA/ODA based PIF. The crosslinked PIFs still exhibited excellent thermal stability with 5% weight loss temperatures higher than 520°C. In the field with frequency higher than 100 Hz, the dielectric constants of the obtained PIFs ranged from 1.77 to 2.4, and the dielectric losses were smaller than 3 × 10^?2 at 25–150°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1734–1740, 2006     

Study on structure-property relationship of polyimide blends

Summary Three pairs of polyimide/polyimide blends (50/50 wt%) with different molecular structures were prepared by two ways, i.e. mixing of the polyamic acid precursors with subsequent imidization, and direct solution mixing of the polyimides. The blends were studied with DMA technique. The results obtained show that all the blends prepared with these two different ways are miscible, as there existed only one glass transition temperature (Tg) for all the blends. It is suggested that the miscibility of these polyimide/polyimide blends is a result of the strong inter-molecular charge-transfer interaction between the chains of their components.     

Solvent effect on the curing of polyimide resins

The effect of the solvent 1-methyl-2-pyrrolidinone (NMP) on the curing of polyimide resins synthesized from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) has been investigated. Three polyimide precursors, i.e., the polyamic acid (PAA), with controlled amount of NMP were prepared. The study was aimed first to independently investigate the decomplexation process, which involved the evolution of hydrogen-bonded NMP from PAA, without interference from imidization. This was accomplished by TGA at varying heating rates using different solvent content in PAA. The observed one-stage decomplexation process suggested that the complex formation of NMP and PAA was not the same as the model compound studied by others. An average value of 150 kJ/mol for the activation energy of the decomplexation process was obtained. The study then sought to identify the effect of the decomplexation on the imidization kinetics by employing DSC at several drying temperatures and also varying heating rates. This allowed one to control the extent of plasticization that occurred to facilitate the imidization process. Our DSC data showed that over-drying PAA resulted in prolonged imidization due mainly to the lack of plasticization by decomplexed NMP. The estimated enthalpy of imidization and that of decomplexation were 114 KJ/mol and 53 kJ/mol NMP, respectively. Finally, the imidization kinetics was independently investigated using FTIR, without the interference from decomplexation process. The results indicated that there were four stages during the entire imidization process. Up to a temperature of 150°C, less than 20% of amide groups had reacted to give imide groups and the reaction was slow. Most of the imidization took place between 150 and 180°C with conversion as high as 90%. The imidization process was completed after the temperature was further raised to 250°C. Above 250°C, the reverse reaction became more significant (due probably to configurational and packing preference) and resulted in a lowering of final conversion back to 80%. © 1992 John Wiley & Sons, Inc.     

High temperature shape memory polyimide ionomer

In this work, a high temperature shape memory polymer based on polyimide (PI) ionomer is prepared by introducing ionic crosslinked interaction. The ionic crosslinked points are introduced to polymer networks through the reaction between polyamic acid and calcium hydroxide before thermal imidization. The crosslinked reaction, microtopography, mechanical, thermal, and shape memory properties of PI ionomers are systematically investigated. The results show the introduction of ionic crosslinked interaction could enhance the glass transition temperature, mechanical, and shape recovery performance of ODA‐ODPA, a PI. The prepared ionomers exhibit good high temperature shape memory properties around 270 °C. The shape fixation and shape recovery ratio are over 99% and 90%, respectively. This method provided a new sight of preparing high temperature shape memory polymer, which could be used in severe conditions, like aerospace industry field. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43630.     

Comparison of one-pot and two-step polymerization of polyimide from BPDA/ODA

The one-pot method polymerization of polyimide was carried out from 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA) by the use of p-chloro-phenol as the solvent. The behavior of the polymerization was compared with that of the two-step method. The imidization reaction in the one-pot method proceeds completely in this system at even a low temperature such as 100°C. In the course of the film preparation from the solution, the embrittlement occurs when the film is prepared from polyamic acid solution, while it does not occur in the case of that from the solution of the one-pot method. A molecular weight of polyimide film is almost the same as that of precursor polyimide in the solution. In the same way, that of polyimide film is almost the same as that of precursor polyamic acid. The mechanical properties of the polyimide film prepared by the one-pot method are similar to those by the two-step method. © 1996 John Wiley & Sons, Inc.     

Morphology and size control of inorganic particles in polyimide hybrids by using SiO2-TiO2 mixed oxide

Polyimide/inorganic hybrids were prepared by sol-gel reaction starting from tetraethoxysilane (TEOS), and tetrabutyl titanate (TBT) in the solution of polyamic acid in N,N-dimethylformamide. The hybrid films were obtained by the hydrolysis-polycondensation of TEOS and TBT in polyamic acid solution, followed by the elimination of solvents and imidization process. Binary polyimide/SiO₂ and polyimide/TiO₂ hybrids, as well as ternary polyimide/SiO₂-TiO₂ hybrids (with varied ratio of SiO₂ to TiO₂) were prepared to study the effects of the recipes and inorganic components on the morphologies of the polyimide hybrids. Transparent films with much higher inorganic content can be obtained in ternary polyimide hybrids, while lower inorganic content in binary hybrids. The results also indicate that the inorganic particles are much smaller in the ternary systems than in the binary systems, the shape of the inorganic particles and the compatibility for polyimide and inorganic moieties are varied with the ratio of the inorganic moieties in the hybrids. The completely imidization temperature of the polyamic acid was delayed, and furthermore, the thermal stability of polyimide was enhanced through the incorporation of the inorganic moieties in the hybrid materials.     

Characterization of the imidization of the aromatic polyimide LARC-160

The polyimide resin LARC-160 was prepared from diethyl-3,3′,4,4′-benzophenone tetracarboxylate (BTDE), ethyl-5-norbornene-2,3-dicarboxylate (NE), and Jeffamine AP-22. The imidization reactions of NE and BTDE were studied by HPLC, ¹³C-NMR, and IR. NE imidizes slowly at 12°C; BTDE imidizes when the resin is heated above 100°C. Both imidization reactions proceed directly to the imide. Neither amic acid is present in significant quantities at any stage of the imidization reactions. The monomer mixture has been stored at 12°C for periods up to 14 months. The effects of resin aging at this temperature on the chemical composition of the resin monomer mixture and the imidized polymer formed on curing were investigated. Aging the resin monomer mixture has the effect of partially advancing the imidization reaction. Aging also results in the formation of slightly higher-molecular-weight polyimide chains after curing of the resin at 140 and 180°C. Bisnadimide (BNI) is observed as a major reaction product, regardless of resin age.     

Electrical and structural analysis of conductive polyaniline/polyimide blends

Conducting films of dodecylbenzenesulfonic (DBSA)‐doped polyaniline/polyimide (PANI/PI) blends with various compositions were prepared by solvent casting followed by a thermal imidization process. Electrical and physical properties of the blends were characterized by infrared spectroscopy, an X‐ray diffraction technique, thermal analysis, a UV‐vis spectrophotometer, a dielectrometer, and conductivity measurements. The blends exhibited a relatively low percolation threshold of electrical conductivity at 5 wt % PANI content and showed higher conductivity than that of pure DBSA‐doped PANI when the PANI content exceeded 20 wt %. A lower percolation threshold and a lower compatibility was shown between the two components in the blends than those of PANI–camphorsulfonic acid/polyamic acid (PANI–CSA/PAA). A well‐defined layered structure due to the alignment of the long alkyl chain dopant perpendicular to the PANI main chain was evidenced by WAXD spectra. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2169–2178, 1999     

Inkjet printing of polyimide insulators for the 3D printing of dielectric materials for microelectronic applications

In this article, we report the first continuous fabrication of inkjet‐printed polyimide films, which were used as insulating layers for the production of capacitors. The polyimide ink was prepared from its precursor poly(amic) acid, and directly printed on to a hot substrate (at around 160 °C) to initialize a rapid thermal imidization. By carefully adjusting the substrate temperature, droplet spacing, droplet velocity, and other printing parameters, polyimide films with good surface morphologies were printed between two conducting layers to fabricate capacitors. In this work, the highest capacitance value, 2.82 ± 0.64 nF, was achieved by capacitors (10 mm × 10 mm) with polyimide insulating layers thinner than 1 μm, suggesting that the polyimide inkjet printing approach is an efficient way for producing dielectric components of microelectronic devices. © 2016 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43361.     

Simulation of dry‐spinning process of polyimide fibers

As one type of high‐performance fibers, the polyimide fibers can be prepared from the precursor polyamic acid via dry‐spinning technology. Unlike the dry‐spinning process of cellulose acetate fiber or polyurethane fiber, thermal cyclization reaction of the precursor in spinline with high temperature results in the relative complex in the dry‐spinning process. However, the spinning process is considered as a steady state due to a slight degree of the imidization reaction from polyamic acid to polyimide, and therefore a one‐dimensional model based on White‐Metzer viscoelastic constitutive equation is adopted to simulate the formation of the fibers. The changes of solvent mass fraction, temperature, axial velocity, tensile stress, imidization degree, and glass transition temperature of the filament along the spinline were predicted. The effects of spinning parameters on glass transition temperature and imidization degree were thus discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical Properties and Morphology of Nitrile Rubber Toughened Polystyrene

Mechanical properties and morphology of blends of polystyrene and finely powdered (uncrosslinked and crosslinked) nitrile rubber were studied with special reference to the effect of blend ratio. Blends were prepared by melt mixing polystyrene and nitrile rubber in an internal mixer at 180°C in the composition range of 0–20 wt% nitrile rubber. The tensile stress/strain properties and impact strength of the polystyrene/nitrile rubber blends were determined using injection molded test specimens. In comparison to the blends with uncrosslinked nitrile rubber, blends with crosslinked nitrile rubber showed higher tensile strength, elongation at break, Young's modulus, impact strength, flexural strength, and flexural modulus. The enhanced adhesion between the dispersed nitrile rubber phase and the polystyrene matrix results in an increase in mechanical properties. Scanning electron micrographs of the fractured surfaces confirm the enhancement in mechanical properties.     

Preparation and properties of polyimide solvent‐resistant nanofiltration membrane obtained by a two‐step method

This study investigated the preparation of polyimide solvent‐resistant nanofiltration membranes by a two‐step method (casting the membrane first and then crosslinking by the thermal imidization method). The influences of polymer concentration, thickness of membranes, temperature of the imidization, phase inversion time and thermal imidization procedure were studied. The membranes with the highest rejection rate of Fast Green FCF (molecular weight 808.86 g mol^?1) were prepared in the following conditions: polymer concentration 13 wt%, phase inversion time 1 h, membrane thickness 150 µm and thermal imidization procedure 200 °C for 2.5 h, 250 °C for 2 h and 300 °C for 2 h in a vacuum environment; the heating rate was 5 °C min^?1. The membrane was stable in most of the solvents tested and the fluxes of some common solvents were equal to or higher than a number of commercial solvent‐resistant nanofiltration membranes. A much higher rejection of dyes in water than in methanol was observed in the filtration experiments and a new way to explain it was developed. Copyright © 2011 Society of Chemical Industry     

Forced torsional properties of PMR composites with varying nadic ester concentrations and processing histories

PMR polyimide resin was prepared from 4,4′-methylenedianiline (MDA), the dimethyl ester of 3,3′,4,4′- benzophenonetetracarboxylic acid (BTDE) and the monomethyl ester of 5-norbornene-2,3-dicarboxylic acid (NE). The NE group serves as a chain terminator and crosslinking site. PMR/Celion 6000 composites were fabricated from resins having varying NE concentrations using two molding processes, and the laminates characterized in forced torsion. Glass transition temperatures (T_g) of 360–390°C were observed in the crosslinked resins, as compared with the literature value of 284°C reported for the uncrosslinked systemT_g did not decrease with decreasing NE concentrations over the range from 2.0 to 1.25 moles. Stoichiometry, within the range studied, showed little influence on shear properties; however, a 25% variation in matrix shear modulus with processing was observed. The G₁₂ values determined in forced torsion were in excellent agreement with those reported from tensile tests of ±45° laminates. A branching and possible secondary crosslink mechanism is proposed based on dynamic mechanical behavior and infrared spectra of the composites.     

Adhesion and interface studies between copper and polyimide

The adhesion and interface structure between copper and polyimide have been studied. Polyimide films were prepared by spinning a polyamic acid solution (Du Pont PMDA-ODA) in an NMP solvent onto a Cu foil, followed by thermal curing up to 400°C. The adhesion strength was measured by a 90° peel test. The peel strength of 25 μm thick Cu foil to 25 μm thick polyimide substrate was about 73 g/mm with the peel strength decreasing with increasing polyimide thickness. Cross-sectional TEM observation revealed very fine Cu-rich particles distributed in the polyimide. Particles were not found closer than 80-200 nm from Cu boundary. These Cu-rich particles were formed as a result of reaction of polyamic acid with Cu during thermal curing. We attribute the high peel strength to interfacial chemical bonding between Cu and polyimide. This behavior is in contrast to vacuum-deposited Cu onto fully cured polyimide.     

Simulation of polyimide fibers with trilobal cross section produced by dry‐spinning technology

As one type of high performance fibers, polyimide fibers can be prepared from polyamic acid (PAA) solution by dry‐spinning technology. The transformation from the precursor of polyamic acid to polyimides via thermal cyclization reaction in the dry‐spinning process is a main distinguishing feature, which is very different from other fibers produced by dry‐spinning such as cellulose acetate fiber and polyurethane fiber. In this report, the dry‐spinning formation of polyimide fibers with trilobal cross section from PAA solution in N,N‐dimethylacetamide is simulated via a one‐dimensional model based on a viscoelastic constitutive equation, combined with profile degree equation of cross section and imidization kinetics equation. The glass transition temperature, imidization degree and profile degree of the filament along the spinline are predicted by the model, as well as relative parameters such as solvent mass fraction and temperature. As a simulated result, solidification of polyimide fibers take place about 150 cm from the spinneret which is farther than for cellulose acetate fiber (70 cm). Moreover, the final profile degree of fiber is affected by many spinning parameters, such as spinning temperature, surface tension, spinning solution concentration, major, and minor axis length of the spinneret hole. POLYM. ENG. SCI., 55:2148–2155, 2015. © 2015 Society of Plastics Engineers     

Effect of zone drawing accompanied with crosslinking on the structure and properties of ultrahigh molecular weight polyethylene gel film

To enhance the thermal properties of ultrahigh molecular weight (UHMW) (viscosity-average molecular weight of 6 × 10⁶) polyethylene (PE) gel film, this was crosslinked by dicumyl peroxide (DCP) during a high-temperature zone drawing, which is effective to orient film. Through a series of experiments, it turned out that crosslinking actualized by an optimum amount of DCP and high-temperature zone drawing technique caused significant changes in the structure and properties of UHMW PE gel film. That is, crosslinking increased storage modulus of UHMW PE gel film at 25°C, resulting in improving thermal properties of the film. On the contrary, the crosslinking effect played a hindering role in raising the draw ratio of UHMW PE gel film. Maximum storage modulus of 165 GPa at 25°C could be obtained at the draw ratio of 324 of uncrosslinked homo-PE gel film. In the case of crosslinked PE gel film, the highest storage modulus at 25°C reached 65 GPa at maximum draw ratio of 150. Crosslinked film exhibited high modulus, even at 190°C, to some extent, while uncrosslinked homo-PE gel film was molten completely at 150°C. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1583–1590, 1997     

Influence of chemical structure of polyimide prepolymer on rheo‐mechanical properties of polyimide foam composites

A study is reported of the effect of varying chemical composition of foam polyimide prepolymers (H‐complex) on the structure and properties of foam polyimide resins and their composites with aromatic polyimide fiber felt. The melt rheological behavior of the H‐complex was found to be strongly dependent on its chemical composition and structure reorganization in the melt which is akin to mesophasic structural transition states in liquid crystal polymers. Changing the diamine part of the H‐complex from 4,4‐methylene dianiline to 1,3‐diaminobenzene led to decreased steady shear viscosity at temperatures and shear rates ranging between 95° and 105°C and 0.01 and 1 s⁻¹, respectively. Additionally, changing the dialkyl moiety from dimethyl to diethyl in 3,3′,4,4′‐benzophenonetetracarboxylic dialkyl ester (precursor to the H‐complex) increased gelation time of the H‐complex, enhancing processibility of the foam polyimide composites. The results indicate that novel, lightweight foam polyimide composites with enhanced thermomechanical properties for beneficial uses can be prepared through chemical modification of the H‐complex prior to its thermal imidization in the presence of the aromatic polyimide fiber felt.     

Synthesis and characterization of a positive‐working,aqueous‐base‐developable photosensitive polyimide precursor

A positive‐working, aqueous‐base‐developable photosensitive polyimide precursor based on poly(amic ester)‐bearing phenolic hydroxyl groups and a diazonaphthoquinone photosensitive compound was developed. The poly(amic ester) was prepared from a direct polymerization of 2,2′‐bis‐(3‐amino‐4‐hydroxyphenyl)hexafluoropropane and bis(n‐butyl)ester of pyromellitic acid in the presence of phenylphosphonic dichloride as an activator. Subsequently, the thermal imidization of the poly(amic ester) precursor at 300°C produced the corresponding polyimide. The inherent viscosity of the precursor polymer was 0.23 dL/g. The cyclized polyimide showed a glass‐transition temperature at 356°C and a 5% weight loss at 474°C in nitrogen. The structures of the precursor polymer and the fully cyclized polymer were characterized by Fourier transform infrared spectroscopy and ¹H‐NMR. The photosensitive polyimide precursor containing 25 wt % diazonaphthoquinone photoactive compound showed a sensitivity of 150 mJ/cm² and a contrast of 1.65 in a 3 μm film with 1.25 wt % tetramethylammonium hydroxide developer. A pattern with a resolution of 10 μm was obtained from this composition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 352–358, 2002