A low dielectric constant polyimide/polyoxometalate composite

A silane‐modified mono‐lacunary Keggin‐type polyoxometalate (POM), (Bu₄N)₄[SiW₁₁O₃₉{(CH₂?CH? Si)₂O}] (SiW₁₁? CH?CH₂), was obtained by reaction of vinyltrimethoxysilane with K₈(SiW₁₁O₃₉) in acidic MeCN/H₂O mixed solutions. Then, the modified polyoxometalate was physically blended with the pyromellitic dianhydride (PMDA)‐4,4′‐oxydianiline (ODA) poly(amic acid) and the blends were thermally imidized to form polyimide/ polyoxometalate composites. The X‐ray diffraction (XRD) analysis indicates that the polyoxometalate clusters cannot form crystalline structures in the composite, suggesting that the blending leads to improved compatibility between the polymer matrix and the modified polyoxometalate. The EDS (W‐mapping) studies on the composite films reveal that the polyoxometalate clusters are well dispersed in the polyimide matrix. The physical incorporation of modified POM into polyimide remarkably reduced the dielectric constant of the latter from 3.29 to 2.05 when 20 wt% of SiW₁₁? CH?CH₂ was used. Besides, the addition of the modified POM into polyimide increased the storage modulus of polyimide without severely affecting its thermal properties. Copyright © 2009 John Wiley & Sons, Ltd.     

Controllable porous fluorinated polyimide thin films for ultralow dielectric constant interlayer dielectric applications

In this paper, silica microspheres were used as template to prepare porous fluorinated polyimide (FPI) thin films from polyamic acid (PAA, precursor of FPI) and silica colloid solution. The strong hydrogen-bonding interaction between silica microspheres and PAA chains have improved the dispersion of silica microspheres in N,N-Dimethylformamide (DMF) solution, resulting in the high weight content of silica template in PAA/silica colloid solution, and thus giving rise to the formation of porous FPI films with maximum porosity of 35%. The interior microstructures of the resultant porous FPI thin films were investigated. It is found that the porous FPI thin films have interconnected “ink-bottle-type” porous structure, and the pore size, porosity could be precisely controlled by the diameter and weight content of silica microspheres, respectively. Although both the tensile strength and young modules declined with the increasing porosity, the high level void of the porous FPI films endowed the FPI ultralow dielectric constant of 1.84 when the porosity increased to 35%. Furthermore, the mechanical and dielectric properties of the porous FPI films were closely related to the microstructures and porosity, indicating the desired properties could be controlled to meet the application in the microelectronics.     

Cell processing on polyimide surface patterned by rubbing

In this study, we prepared a novel rubbed fluorinated polyimide film using a rubbing machine with a rubbing cloth and determined the surface properties of the rubbed film using an atomic force microscope and contact angle measurements. In addition, we evaluated the cell adhesion behavior on the rubbed polyimide film using a phase contrast microscope. Interestingly, a rubbed polyimide surface having a micrometer‐scale grooved pattern was prepared by the rubbing method, and the morphologies of rat primary hepatocytes and human liver cell lines attached to the rubbed surface were three‐dimensional multicellular spheroids, while the cells on an unrubbed surface showed two‐dimensional monolayers. This initial study indicates that the rubbing method without any chemical modification is simple and can easily produce large surface areas, suggesting that the rubbing may become a novel cell culture method. Copyright © 2008 John Wiley & Sons, Ltd.     

Fluorinated polyimide nanocomposites for CO2/CH4 separation

The purpose of this project was to synthesize fluorinated polyimide (PI) nanocomposite membranes in order to study the gas permeation rates and selectivity of carbon dioxide and methane. PIs were synthesized from 2,2‐bis(3,4‐anhydrodicarboxyphenyl)hexafluoropropane (6F dianhydride, 6FDA) and 4,4′‐diaminodiphenyl ether (oxydianiline, ODA) into which were incorporated nanoparticulate additives as follows: in situ TiO_2, both plain and treated with dodecyl sulfate surfactant, and organo‐clay (Cloisite®‐10 Å) at loads of 1, 3, and 5 wt% to the polyamic acid. Polyamic acid films were solvent cast, cured at 200°C then post‐cured at 300°C and measured for permeation data and for thermal properties. Glass transition temperatures ranged from 124 to 140°C for the cured PIs and from 142 to 147°C for the post‐cured materials, the nano‐inclusions having little discernable effect on this property. Thermogravimetric analysis (TGA) data show that the inclusion of Cloisite® or TiO₂ caused a small decrease of thermal stability from 555°C to about 532 to 541°C. The inclusion of clay causes a decreased permeation rate while the addition of TiO₂ improves the rate and selectivity. Treating the nanofillers with surfactant decreases selectivity and marginally increases rate of permeation of CO₂. Post‐curing caused a darkening of the composites, but not the neat PI. This heat treatment also resulted in a significantly decreased permeation rate, but a significantly increased selectivity. The resulting material shows superior gas separation properties to the commercially available PI, Matrimid® produced by Ciba‐Geigy. Copyright © 2008 John Wiley & Sons, Ltd.     

Fibers from a low dielectric constant fluorinated polyimide: Solution spinning and morphology control

Control of the internal morphology of wet-spun fibers from a fluorinated polyimide has been achieved by varying the rate of polymer coagulation through adjustments in nonsolvent/solvent miscibility and precipitation strength of the coagulation bath. Filament internal morphologies ranged from very porous or sponge-like to fully solid. Intermediate structures included fibers containing a spongy core with a nonporous skin, sponge-like fibers containing large voids, and a relatively solid material containing randomly spaced small voids. The cross-sectional shape of the fiber is dependent upon the coagulation process as well as the volume contraction of the initial extrudate. Drawn fibers (3×) retained the original asspun cross-sectional shape and also lost porosity. Mechanical properties of poly(6FDA-4BDAF) fibers have an inverse relationship to filament porosity. Maximum modulus and break strength for drawn fibers is approximately 6 CPa and 200 MPa, respectively. Asspun mechanical properties were dependent upon the processing conditions and have moduli between 0.4–3.0 Gpa and break strengths of 10–160 MPa. A dielectric constant of 2.50 for nonporous films was measured over a frequency range between 1.0 MHz to 1.8 GHz, showing little dispersion. © 1997 John Wiley & Sons, Inc.     

Photoreactive fluorinated polyimide protected by tetrahydropyranyl (THP) group based on chemical amplification: Acid generation in polyimide film and lithographic properties

The photochemistry of photoacid generator (PAG), diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS) and diphenyliodonium 8-anilinonaphthalene-1-sulfonate (DIANS) was investigated in both alkalinesoluble polyimide (6FDA-AHHFP) and novolak films. The quantum yields of photodissociation of DIAS and DIANS in both 6FDA-AHHFP and novolak films. The quantum yields of photodissociation of DIAS and DIANS in both 6FDA-AHHFP and novolak films were determined as 0.11, 0.21, 0.12 and 0.26, respectively. On the other hand, the quantum yields for acid generation from DIAS and DIANS in both of these films were 0.07, 0.18, 0.09 and 0.22, respectively, in the presence of an acid indicator. These results indicate that the values of the quantum yields of photodissociation and photoacid formation for DIAS and DIANS in 6FDA-AHHFP film are lower than those in novolak film. In order to elucidate the lowering of the quantum yields in 6FDA-AHHFP film, fluorescence quenchings of sodium 9,10-dimethoxy-anthracene-2-sulfonate and ammonium 8-anilinonaphthalene-1-sulfonate by a model compound of polyimide was carried out in acetonitrile. The fluorescences of these two salts were efficiently quenched by the model compound with the diffusion-controlled rate constant in acetonitrile, suggesting that a strong electron-accepting capability of the imide carbonyl group may hinder the electron transfer process within PAG molecules in 6FDA-AHHFP film. Although a polyimide (6F-THP) protected by tetrahydropyranyl group is insoluble in aqueous base, 6F-THP film containing PAG became soluble in a 2:1 mixture of 2.0 wt% tetramethylammonium hydroxide (TMAH) and methanol by exposure to 365 nm light and successive post-exposure baking (PEB) at 120°C for 10 min. The sensitivity and contrast of 6F-THP with DIANS after the PEB conditions mentioned above were 110 mJ/cm² and 3.7, respectively. A high-resolution pattern with a good profile was transferred into the 3 μm thickness of the 6F-THP film.     

Low dielectric materials from fluorinated polybenzoxazines

Fluorinated monomers containing a benzoxazine moiety have been synthesized successfully by preparing the benzoxazines from fluorinated amines (4‐fluoroaniline, 2,4‐difluoroaniline, and 2,3,4‐trifluoroaniline). These monomers were polymerized by step curing process following a cure cycle of 100, 150, 200 and 250°C for 1 h at each temperature. The molecular structure of the monomers and their polymers was characterized by Fourier transform infrared and nuclear magnetic resonance techniques. The synthesized fluorinated polybenzoxazines were able to reduce the dielectric constant to 2.0 for polybenzoxazine from 2,3,4 trifluoroaniline (PTF)‐Bzo at a frequency of 1 MHz. Moreover, they possess high thermal stability and low moisture absorption, which makes it suitable for high‐temperature process of interlayer dielectrics. Copyright © 2014 John Wiley & Sons, Ltd.     

静电纺丝法制备MgO纳米纤维

以聚乙烯醇(PVA)作为络合剂与醋酸镁反应制得前驱体，采用静电纺丝法制得聚乙烯醇(PVA)／醋酸镁复合纤维，经焙烧后得到分布均匀、具有较高比表面积和多孔结构的。MgO纳米纤维．对所制得的纳米纤维的结晶度、纯度和表面形貌，分别采用X射线粉末衍射、差热一热重分析(TG-DTA)、红外光谱(IR)、扫描电镜(SEM)等分析测试手段进行了表征．结果表明，煅烧温度对纳米纤维的结晶度和形貌有很大影响．     

Fabrication of well‐aligned electrospun nanofibrous membrane based on fluorinated polyimide

We have fabricated novel nanofibrous fluorinated polyimide membranes on a specially designed collector, which is composed of conductive aluminum plates and glass insulator materials and can be removed from the apparatus, using an electrospinning method. We describe the structure and water flux properties of the nanofibrous fluorinated polyimide membranes. The electrospun nanofibers were deposited across the plates and uniaxially aligned to the collector. In addition, the multi‐layer stacked nanofibrous membranes, consisting of three‐dimensionally ordered nanopores, were produced. The pure water fluxes for the stacked membranes were measured, using a stirred dead‐end filtration cell, and were linearly decreased with an increasing deposition time, indicating that the nanopores formed in the nanofibrous membrane were further narrowed due to the regularly accumulated nanofibers. Copyright © 2009 John Wiley & Sons, Ltd.     

New fluorinated thermoplastic elastomers. III. Novel method of synthesis and characterization of alternating fluorinated polyimide/fluorinated polyhybridsiloxane block copolymers via polycondensation

The synthesis of fluorinated polyimide/fluorinated polyhybridsiloxane (FPI–FPHSX) block copolymers was achieved through the polycondensation of α,ω‐dichlorosilane fluorinated polyimides and α,ω‐disilanol fluorinated polyhybridsiloxanes. Three FPI–FPHSX block copolymers with 41, 50, and 76 wt % polyimide were synthesized and characterized by the tuning of the number‐average molecular weight of the soft polyhybridsiloxane segments. The influence of the soft‐segment length on the behavior of the thermoplastic elastomer material was studied, including the surface tension and thermal properties. The thermomechanical properties of the FPI–FPHSX block copolymers were also examined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2237–2247, 2005     

Lowering the dielectric constant of polyimide thin films by swelling with supercritical carbon dioxide

The swelling with supercritical carbon dioxide (sc‐CO₂) of thin films of polyimides having various structures was investigated. It was shown that the degree of swelling is significantly influenced by the solvent which was used for the synthesis of those polyimides, by the solvent which was used for the preparation of thin films and by the conformational rigidity of the polymers. The presence of hexafluoroisopropylidene groups in the main chain of a polymer prevents its swelling with sc‐CO₂. The best results were obtained for polyimide film ULTEM, based on m‐phenylene‐diamine and isopropylidene‐diphenoxy‐bis(phthalic anhydride), synthesized in benzoic acid, whose free volume increased twice and its dielectric constant decreased from 3.15 to 2.45 by swelling with sc‐CO₂. Copyright © 2013 John Wiley & Sons, Ltd.     

A positive-working photosensitive alkaline-developable polyimide with a highly dimensional stability and low dielectric constant based on poly(amic acid) as a polyimide precursor and diazonaphthoquinone as a photosensitive compound

A positive-working photosensitive polyimide precursor based on fluorinated poly(amic acid) (FPAA) and 2,3,4-tris(1-oxo-2-diazonaphthoquinon-4-ylsulfonyloxy)benzophenone (D4SB) as a photosensitive compound has been developed. FPAA was prepared by ring-opening polyaddition of dianhydrides, pyromellitic dianhydride and biphenyltetracarboxylic dianhydride, with diamine, 2,2′-bis(trifluoromethyl)benzidine, in methanol. The FPAA film showed excellent transparency to UV light and good solubility in a wide range of organic solvents. The dissolution behavior of FPAA containing 30 wt % D4SB after exposure was studied, and it was found that the difference of dissolution rate between exposed and unexposed parts was enough to get high contrast due to the photochemical reaction of D4SB in the polymer film. The photosensitive fluorinated polyimide (FPI) precursor containing 30 wt % D4SB showed a sensitivity of 80 mJ cm⁻² and a contrast of 7.8 with 365 nm light when it was developed with 0.3% aqueous tetramethyl ammonium hydroxide solution at room temperature. The FPI film cured up to 360°C had a low coefficient of thermal expansion of 10.3 ppm °C⁻¹ and a low dielectric constant of 3.04. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2261–2267, 1998     

Preparation and characterization of nanoporous polyimide membrane by the template method as low‐k dielectric material

In order to decrease the resistance–capacitance delay and signal crosstalk in ultra large‐scale integrated circuits (ULSIC), dielectric materials with ultra low dielectric constants are developed to be the replacement of silicon dioxide. Introduction of air on the matrix material is an important method to reduce the dielectric constant, and polyimide (PI) is the most promising polymer to prepare porous matrix material for its distinct advantages. PI membrane with nanopores was prepared by the method of template method (i.e. thermolysis of polystyrene nanospheres in the matrix) following the synthesis of template. The nanoporous membrane was characterized by Fourier transformer infrared, scanning electron microscopy, thermogravimetric analysis, and the dielectric constant of which was measured. Results showed that uniform nanopores about 100–200 nm were formed in the PI membrane, and dielectric constant of which was decreased to 2.08 from 3.34. The nanoporous membrane can be applied as potential low‐k dielectric material in ULSIC. Copyright © 2015 John Wiley & Sons, Ltd.     

Interface hydrogen-bonded core-shell nanofibers by coaxial electrospinning

Core-shell nanofibers were prepared by coaxial electrospinning technology,with poly(ethylene oxide) (PEO) as the core while poly(acrylic acid) (PAA) as the shell.PEO and PAA can form polymer complexes based on hydrogen bonding.In order to avoid forming strong hydrogen bonding complexes at nozzle and blocking spinning process,a polar aprotic solvent,N,N-dimethylformamide (DMF),was selected to dissolve PEO and PAA respectively.SEM,TEM and DSC were utilized to characterize the morphology and structure of PEO-PAA core-shell nanofibers.FTIR spectra demonstrated that hydrogen bonding was formed at the core-shell interface.In addition,the PAA shell of the nanofibers can be cross-linked by ethylene glycol (EG) under heat treatment,which increases the stability and extends the potential applications in aqueous environment.     

Emulsion electrospinning: composite fibers from drop breakup during electrospinning

We evaluate the feasibility of electrospinning oil‐in‐water type emulsions. The emulsions had an aqueous solution of polyethylene oxide (PEO) as the continuous phase, and either mineral oil or a polystyrene (PS) in toluene solution as the drop phase. The Taylor cones and electrified liquid jets were stable even when the emulsion drops were as large as a few‐ten microns in diameter. The resulting electrospun PEO fibers incorporated the dispersed phase of the emulsion in the form of drops (in case of mineral oil), or in the form of solid particles (in case of PS). Mineral oil drops appear to be completely encapsulated in the PEO fibers, whereas the PS particles are either incompletely encapsulated, or covered by only a very thin layer of PEO. Calculations show that in both cases, the initially large emulsion drops are broken during the electrospinning process. Copyright © 2007 John Wiley & Sons, Ltd.     

Reactive lyotropic polyimide oligomers

Amine-terminated and maleimide-terminated oligomers of molecular weight 1200–1800 based on 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl and 3,3′,4,4′-biphenylenetetracarboxylic dianhydride were synthesized and characterized for lyotropic liquid crystalline behavior. Several different synthetic procedures were evaluated and a one-step procedure in m-cresol was found to be the most effective for producing fully imidized materials. Lyotropic behavior was observed only for the as-prepared solutions in m-cresol and in dilutions of this solution. Oligomer thermal stability was excellent, onsets of decomposition were in excess of 550°C. © 1996 John Wiley & Sons, Inc.     

Preparation of polyimide/BaTiO3‐nanocrystal hybrid thin films and their dielectric property

High dielectric constant is highly desirable in capacitors and memory devices. In this work, oleic acid (OA)‐capped BaTiO₃ nanocrystals were synthesized by a two‐phase approach. Polyimide (PI)/BaTiO₃‐nanocrystal composite thin films with high dielectric constant have been successfully fabricated. The morphologies and dielectric properties of the hybrid films were exploited. The results showed that BaTiO₃ nanocrystals can be uniformly dispersed in the PI thin films owing to the surface modification of OA‐capped BaTiO₃ nanocrystals. It was found that the dielectric constant of composite film varies with the volume fraction of BaTiO₃ nanocrystals and sintering temperatures and reaches a maximum value of 44.1, which is around 13 times higher than that of pristine PI thin film (3.2). These results demonstrated that PI/BaTiO₃‐nanocrystal composite films have considerable application potential in microelectronic fields.     

Preparation of three‐dimensional structure controllable nanofibers by electrospinning

The size of “bowl‐like” structures woven by nanofibers could be controlled by adjusting the distance from the nozzle to a modified collector and the voltage applied to the electrospinning device. More interestingly, the nanofibers in the side wall of the “bowl” could vibrate up and down with the changing of the voltage. This voltage‐induced vibration might have potential applications for bio‐mimic process and micro‐motor devices. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of mesoporous functional hematite nanofibrous photoanodes by electrospinning

Iron(III) oxide (hematite, Fe₂O₃) nanofibers, as visible light‐induced photoanode for water oxidation reaction of a water splitting process, were fabricated through electrospinning method followed by calcination treatment. The prepared samples were characterized with scanning electron microscopy, and three‐electrode galvanostat/potentiostat for evaluating their photoelectrochemical (PEC) properties. The diameter of the as‐spun fibers is about 300 nm, and calcinated fibers have diameter less than 110 nm with mesoporous structure. Optimized multilayered electrospun α‐Fe₂O₃ nanostructure mats showed photocurrent density of 0.53 mA/cm² under dark and visible illumination conditions at voltage 1.23 V and constant intensity (900 mW/cm²). This photovoltaic performance of nanostructure mats makes it suitable choice for using in the PEC water splitting application as an efficient photoanode. This method, if combined with appropriate flexible conductive substrate, has the potential for producing flexible hematite solar fuel generators. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and properties of ultralow dielectric porous polyimide films containing adamantane

A series of novel ultralow dielectric porous polyimide (PI) films containing adamantane groups was prepared via the thermolysis of polyethylene glycol (PEG) oligomers mixed into PI matrix. Scanning electron microscopy results indicated that the porous PI films showed closed pores with an average diameter of 120 ± 10 nm. Good thermal properties with 5% weight loss temperature of 499 °C in air atmosphere and glass transition temperature in excess of 310 °C were shown for porous PI films. Notably, the ultralow dielectric constant of porous PI films with 1.85 at 1 MHz was obtained and revealed via broadband dielectric spectroscopy. The effects of the chemical structure of the PI matrix and PEG content on the decomposition behavior of PEG and the performance of porous films were investigated. Wide‐angle X‐ray diffraction results indicated that the PI matrix with large d‐spacing generated weaker interactions between the PEG and PI backbone than those of PI matrix with small d‐spacing. As a result, the PEG for the PI matrix with large d‐spacing was completely decomposed. As indicated by the broadband dielectric spectroscopy results, lower dielectric porous PI films were prepared when the PEG contents in the PI matrix increased from 0 to 20 wt %. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 549–559