ABSTRACTS
The following is a list of the abstracts for papers which will be presented in THE SECOND INTERNATIONAL SYMPOSIUM ON POLYIMIDES AND OTHER HIGH TEMPERATURE POLYMERS: SYNTHESIS, CHARACTERIZATION AND APPLICATIONS. The listing is alphabetical by presenting author. This list is updated continually to add abstracts as they become available and make appropriate corrections. This list may be conveniently searched by using the editor provided with most popular browsers (e.g. Microsoft Explorer, Netscape, ... etc.)
Vanda Yu. Voytekunas2 and Marc J.m. Abadie2
1) Institute of Chemical Sciences, Academy of Science Kazakh, 4800100 Alma-Ata - Kazakhstan
2) Laboratory of Polymer Science & Advance Organic Materials - LEMP/MAO - CC 021, Université Montpellier 2, S.T.L., 34095 Montpellier Cedex 05 - FRANCE
Metallized Polyimide Films with High Reflectivity
Polyimide films (Kapton, Upilex) were metallized by heterogenous chemical modification.
The process consists of three steps :
-- hydrolysis in alkali solutions,
-- chelation by metal cations (Ag+, Co2+, Ni2+, Cu2+)
-- followed by reduction in solution of sodium borohydrate.
Surface modification of polyimide films resulted in the formulation of strong metal coatings.
Thus obtained, metallized films are characterized by high reflectivity in the VIS-IR region, which was measured by IFS 66v/s Brucker spectrometer at normal angle of incident light. Reflectivity coefficients at the most intensive wave band of solar irradiation ( = 531 nm) are for :
-- Ag = 95%,
-- Co = 55%,
-- Ni = 60%.
The films have also been studied and analyzed by X-ray diffractometry, Raman, XPS, Auger spectroscopies, SEM and TEM analysis.
High reflectivity of the films is due to the formation of unique homogenous layer which consists of metal grains of 0.4 - 0.5 m in size.
Polymers for encapsulation of flexible Organic Light Emitting Displays
(Abstract not yet available)
1) Institut fur Neue Materialien, D-66123 Saarbrucken, Germany
2) Department of Chemistry, Quaid -i-Azam University, Islamabad-45320, PAKISTAN
Mechanical and Thermal Properties of Compatibilized Polyimide-Silica Nano-Composites
A new class of organic-inorganic hybrids based upon the polyimide and silica nanoparticles have been prepared. Polyamic acid using pyromellitic dianhydride and 4,4-oxydianiline and 2,2-Bis(3- amino-4-hydroxyphenyl)hexafluoropropane was prepared. The use of the monomer 2,2-Bis(3-amino-4-hydroxyphenyl)hexafluoropropane provided hydroxyl groups along the polymer chain which were used as connecting points to bind silica particles. 3- isocyanatopropyltriethoxysilane coated silica nano-particles were prepared and combined with the polyamic acid. Thin films obtained by the solvent elution technique were cured at 100oC, 200oC and 300 C. These polyimide-silica hybrid films were found to be transparent till 35 wt % of silica. The structure and physical properties of the resulting hybrids were studied by FTIR, TGA, DMTA, TMA, micro-indentation and stress-strain analysis. Universal hardness and reduced modulus increased while coefficient of thermal expansion decreased with increasing silica content. Tensile strength increased initially and then plateau was found with further increase in the silica content. Storage modulus increased both below and above glass transition temperatures. A considerable increase in -relaxation temperature relative to pure matrix was observed for the hybrids containing hydroxyl groups in the matrix while no such shift was observed in case of hybrids from the matrix having no OH groups. Decomposition temperatures taken as 5 wt.% loss as determined from TGA was in the range of 490-540 C and the residue at 900 C was found proportional to the silica contents in the composite.
Tokoro1, Hiroshi Nakagawa1 and Hiroshi Itatani2
1) National Institute of Advanced Industrial Science and Technology (AIST)
Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568 JAPAN
2) PI Research and Development Co., Ltd.
Electrical Properties of Photosensitive Polyimide Thin Films for Integrated Circuit Application
Photosensitive polyimide is expected as a future interlayer dielectric in LSI circuits. Fine contact holes are realized without an etching process. But the ordinary photosensitive polyimide dose not have sufficient pattern resolution and heat resistance for fabrication of LSI circuits. PI R&D Co. and AIST have already developed a fine-resolution positive photosensitive polyimide synthesized by block-copolymerization. In this paper, we report the electrical properties of the photosensitive polyimide thin films used in integrated citcuits. The dielectric constant was measured by cavity resonance method and thin film capacitor method for a wide frequency range from 100 KHz to 20 GHz. The effect of photosensitive materials on the dielectric contant was investigated. The break down voltage and the leackage current were also discussed.
Machine Dynamics and Maintenance Engineering Centre (ITMMEC)
* Centre for Polymer Science and Engineering (CPSE), Indian Institute of
Technology, Delhi, Hauz Khas, New Delhi 110016, INDIA.
Influence of Aramid Fabric on Fretting Wear Performance of Polyetherimide Composite
Polyetherimide (PEI) is, a high temperature engineering thermoplastic polymer (Tg 218C and m. pt. 380C) with very good combination of mechanical and electrical properties along with easy injection mouldability. Its fibre reinforced and solid lubricated composites have shown excellent tribological potential in adhesive wear mode. In fretting wear mode, however, very little is reported in the literature on short fibre reinforced and solid lubricated composites of PEI but not on fabric reinforced composites. Authors have reported in their earlier papers on the significant potential of carbon fabric for improving fretting wear performance of PEI. In this paper efforts have been devoted to explore the tribo-potential of aramid (Kevlar 29) fabric for improving fretting wear performance of PEI. It was observed that aramid fabric (lighter and less expensive than the carbon fabric) improved the fretting and wear behavior of PEI significantly. The friction coefficient of PEI (0.4) was independent on operating conditions while that of aramid composite (CAF) very much depended on load and temperature. Overall, fabric inclusion reduced the friction coefficient of PEI from 0.4 to 0.3 and specific wear rate by 3 times which is very significant improvement. The tribo- performance improvement capability of AF, however, slightly deteriorated at high operating temperature (150-200C). The studies on worn surface by SEM proved to be very helpful in understanding wear mechanisms. It was observed that high temperature (200C) is more damaging to the fabric and hence to the performance of composite rather than the higher load (200 N).
Industrial Tribology, Machine Dynamics and Maintenance Engineering Centre
(ITMMEC)
* Centre for Polymer Science and Engineering (CPSE)
Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110 016.
#Indian Institute of Technology, Mumbai, Powai, Mumbai 400 076.
Gharda Chemical Ltd., Mumbai.
Wear Behavior of PEEK- PTFE Blends
Polyetheretherketone and PTFE are high temperature and high performance tribo- polymers. PEEK is known for its excellent combination of thermal and mechanical properties. Composites of PEEK (filled with solid lubricants and reinforced with short fibres or both) form one of the best class of tribo- materials. Neat PEEK, however, is not a good tribo-material inspite of its very good mechanical properties and resistance to wear and chemicals, since it shows stic- slip behavior under even moderate sliding conditions. PTFE, on the other hand, exhibits best friction behavior, but poor wear performance. The blends of PEEK and PTFE hence, are expected to exhibit better combination of friction and wear behavior rather than the individual. In the case of adhesive wear mode, it has been reported in the literature. No studies, however, have been reported on such blends in fretting wear mode. Hence the paper focus on the fretting wear aspects and related mechanisms of such blends. Five blends of PEEK containing PTFE in 0, 7.5, 15, 22.5 and 30% were prepared and characterized for their various properties such as compositional, thermal and mechanical. The fretting wear studies on the pin on disc configuration (polymer pin against mild steel disc) under various loads were performed keeping amplitude, frequency and operating temperature constant. Neat PTFE was also studied in the identical conditions for comparison. It was observed that inclusion of PTFE in PEEK resulted in significant enhancement in fretting wear performance. The PV limit at which stick-slip behaviour was shown, increased considerably for a blend with 7.5 % PTFE. For further inclusion, the stic-slip behavior was not observed. With increase in percentage of PTFE, friction coefficient decreased very significantly (0.43 to 0.05). Moreover, specific wear rate also decreased very substantially (more than 40 times).
The blend containing 30% PTFE showed the lowest friction coefficient and specific wear rate among the PEEK based materials. The mechanical properties except impact, however, showed exactly opposite behaivour. All other properties deteriorated with inclusion of PTFE upto 30%. Thus the blend 30% was the best in tribological properties but poorest in mechanical properties. SEM studies were done on the samples to understand wear mechanisms.
Polyimides Based on Rhenium(i) Diimine Complexes
The incorporation of diimine complexes of d6 transition metals into organic polymeric matrices is of significant practical interest because of their potential applications in catalysis and solar energy conversion. We have been continuously exploring different polyimides that contain different transition metals. The synthesis of some rhenium containing polyimides is reported. They were prepared by the polymerization between a diamino substituted rhenium tricarbonyl diimine complex with various aromatic dianhydrides. Electronic absorption spectra of the polymers showed a very strong intramolecular charge transfer transition that obscures the transfer transition band due to the rhenium, complex in the visible region. The potential of using the rhenium complex as photosensitizer is studied. The polyimides were fabricated into simple devices to which visible light was irradiated. A large photocurrent response was observed when the polyimide was irradiated at 514 nm.
Synthesis of Aromatic Benzoxazole Polymers For High Tg,Low Dielectric Properties
Next generation microelectronic packaging requirements are driving the need to produce increasingly lower dielectric constant materials while maintaining high thermal stability and ease of processing. Important material requirements for these applications include low dielectric constants, high thermal, thermooxidative as well as dimensional stabilities, Tg's above 350°C, low thermal expansion coefficients and low moisture uptake. Required dielectric constant at the beginning of the 21st century will be between 2.0- 2.4, with a progressive need for a figure of merit below 2.0. Our research efforts have focused on the synthesis and characterization of new polymer compositions with a view to meeting the objectives of imparting high thermal stability (degradation temperature higher than 350°C), low moisture uptake (less than 1 %), solubility for processing in common organic solvents as well as obtaining dielectric constants less than 2.5 and low thermal expansion coefficients; the logical extension of such an approach, recently, has also resulted in some unique post-polymerization chemistry to provide solvent resistance to microelectronic packaging polymer candidate materials after processing.
Surface Modification of Polyimide to Improve the Adhesion Properties of Polyimide-Copper Composites
Flexible polyimide-copper composites with improved stability under rapidly changing thermal and mechanical conditions have been obtained by a pre-treatment of the polyimide surface consisting of a heavy-ion irradiation of the polyimide foil and subsequent etching of the latent ion tracks. During the etching step a special surface-depth relief is created on the surface of the polyimide. Metallizing this polyimide ion-track foil by chemical deposition and electrodeposition of copper leads to a polyimide-copper composite showing improved peel strength and high resistance to thermal and mechanical stress.
Synthesis and Optical Properties of Polyimide-Silica Hybrid Materials
In this study, PMDA-ODA/SiO2 and 6FDA-ODA/SiO2 hybrid optical thin films were synthesized and characterized by using the in-situ sol-gel reaction combined with spin coating and multi-step baking. The hybrid thin films were prepared by an aminoalkoxysilane capped poly(amic acid) and tetramethoxysilane (TMOS) as the precursors. Highly transparent hybrid thin films were obtained at the silica content of 0-55 wt%, and the optical properties can be controlled by the silica content. The FE-SEM study suggests the nano-size domain of the silica moieties in the hybrid materials. AFM results show an excellent planarity in the prepared hybrid thin films. The refractive indices of the prepared PMDA-ODA/SiO2 and 6FDA-ODA/ SiO2 films at 633 nm decrease linearly from 1.659 to 1.532 and 1.568 to 1.517 with increasing the silica content, respectively. The abbe numbers show the opposite trend with the refractive indices. The birefringence of the hybrid films between TE and TM mode refractive indices are decrease from 0.044 to 0.023 for PMDA-ODA/SiO2 hybrid films and from 0.011 to 0.006 for 6FDA-ODA/SiO2 hybrid films, respectively. The results show that the optical dispersion and anisotropy are resulted from the polyimide moieties. The superior optical properties of the 6FDA-ODA/silica films than those of the PMDA-ODA/silica films are due to the fluorine content and the orientation of the polyimide structures. The optical loss of the prepared hybrid thin films can be less than 1dB/cm as the silica moiety added. The prepared hybrid thin films show excellent thermal stability. They have thermal decomposition temperatures higher than 540oC. These results suggest that the prepared hybrid films have potential applications for optical devices, such as waveguides.
Structure Development During Streching and Annealing of Oriented Amorphous Isotactic Polystyrene and Poly(phenylene Oxide) Blends
(Abstract not yet available)
.
Synthesis and polymerization of Macrocyclic Lactamimides: Experimental and Theoretical Study
The ring-opening polymerization of various lactamimide containing macrocycles has been modeled using quantum chemistry tools. It has been established that the ring opening polymerisation of these macrocycles is an enthalpy driven process with ceiling polymerization temperature. Anionic polymerization leads to undesirable side reactions, while the cationic process was found to be more adequate for this type of macrocyclic monomers.
On the base of the molecular modeling results a series of novel macrocyclic lactamimides has been synthesized by pseudo high dilution technique and polymerized cationically in melt to give polylactamimides.
Thin-film Transistor Technology on Thin Polyimide Substrates
Novel display applications, such as electronic paper, smart labels, and displays for vehicular applications, require flexible TFT backplanes. Future sensor skins and electrotextiles will be based on flexible circuits. Therefore, the traditional glass substrate of thin-film transistor technology has to be replaced with foils of plastic or metal. For this reason we have developed amorphous silicon (a-Si:H) thin-film transistor (TFT) technology on thin foils of polyimide.
Among the polyimides we have chosen Kapton® E. It has a relatively high glass transition temperature, a surface roughness that can be tolerated by the 1-mm thick TFTs, and its coefficient of thermal expansion is closer to that of amorphous silicon (a-Si:H) and silicon nitride (SiNx) than most polymers. Kapton E is chemically stable and does not require any pre-shrinking procedures. Nevertheless, our TFT technology is optimized for the maximum process temperature of 150ºC for eventual use on other polymer film substrates. A key aspect of using organic polymers as substrates for TFT electronics is the initial surface passivation. In effect the passivation layer converts the chemistry of the polymer foil to the chemistry of the passivating material. The passivation layer also serves as a mechanical bond.
We fabricated arrays of a-Si:H TFTs on 51 mm thick polyimide at the
temperature of 150°C. First, the polyimide substrate was coated on both
sides with a 0.5 µm thick passivation layer of SiNx. All TFTs had the bottom-gate structure consisting of: ~ 100 nm thick Ti/Cr layer as gate electrode, ~
360 nm of gate SiNx, ~ 100 nm of undoped a-Si:H, 180 nm of passivating
SiNx, ~ 50 nm of (n+) a-Si:H, and ~ 100 nm thick Al for the source-drain
contacts. The typical parameters of these devices are: off-current is
~ 3x10-12 A, the on-off current ratio > 106, the threshold voltage ~ 3 V, the
subthreshold slope ~ 0.5 V/decade, and the electron mobility in the
saturation regime is ~ 0.7 cm2/Vs. This confirms that the performance of
our flexible TFTs is comparable to that of standard a-Si:H TFTs fabricated at
temperatures of 250ºC-350ºC on glass. (This work is supported by DARPA,
NSF, and NJCST)
Semicrystalline Polyimide DABP-BTDA Modified by Fullerenes for Wear Protection
1) Institute of Macromolecular Compounds, Russian Academy of Sciences,
St.Petersburg 199004, V.O.Bolshoy pr. 31, Russia.
2) Institute of Problems of Mechanical Engineering, Russian Academy of Sciences, St.Petersburg 199178, V.O.Bolshoy pr. 61, Russia.
This work investigates some tribological properties of melt processable semicrystalline polyimide (Tg=250oC, Tm=290oC) based on 3,3'- diaminobenzophenone and 3,3',4,4'- benzophenonteracarboxylic dianhydride (DABP-BTDA) and doped by fullerenes. The mechanical properties of this polyimide molding parts are as follows at: flexural strength is 120 MPa, flexural modulus is 2.2 GPa, and elongation at break is 5.5 %. As it was shown earlier [1], polyimide crystalline content depends mainly on the synthesis procedure (chemical or thermal imidization) and kind of the solvent. Fullerene extract (60 - 78%, 70 - 22%) in the amount of 0.1 wt.% was added to polyimide at different stage of its chemical imidization. DSC analysis did not show sufficient influence of fullerene adding on polyimide melting temperature and heat flow.
Some tribological characteristics were investigated under dry friction condition for different polyimide/fullerene molding parts depending on their synthesis procedure. The main parameters were a sliding friction coefficient for steel rod on polymer samples and weight wear for 10 min of work at each nominal pressure in tribocontact. It was found that optimal tribological properties are possible to obtain for polyimide/fullerene samples when fullerene was introduced into the diamine solution at the stage of chemical imidization. The sliding friction coefficient of these samples has increased from 0.18 to 2.0 at the investigated pressure range (the maximum pressure attained was 8 MPa). These samples have shown also minimal weight wear under experimental conditions as compared with polyimide samples without adding of fullerenes. Wear particles and moldings contact surfaces were analyzed with the aid of optical microscope. The analysis has detailed the influence of sliding velocity and pressure in tribocontact on surface damage.
1.Kalbin A.G., MeleschkoT.K., Kudruavtsev V.V., Bogorad N.N., Lukasov S.V., BaklaginaYu.G. Effect of imidization condition on the supermolecular structure of polyimide based on 3,3' - diaminobenzophenone and 3,3',4,4'- benzophenonteracarboxylic dianhydride (BTDA-DABP) .//Int. Symposium "New Approach in polymer synthesis and macromolecular formation", June 16-20, 1997, St.-Petersburg, P-027
Deposition of Copper Thin Film on Chemically Modified Polyimide Surface
The polyimide (PI) has been widely used in microelectronics packaging due to its low dielectric constant, good thermal and mechanical stability, and excellent chemical resistance, for example, its use as an insulator in the multi-chip module (MCM) is being investigated. However, the adhesion of the polyimide with metals is normally rather poor. To enhance the adhesion strength between PI films and metals, surface modifications on PI side is a logical choice. Recently, wet treatment method has received special attention since it relies on the nucleophilic ring-opening reaction by a base, which is a cost effective approach. If the concentration of base, the temperature and the time of treatment are carefully controlled, the reaction can be restricted to the surface of a PI film. In our recent study, Upilex-S® [poly(biphenyldianhydride-p-phenylenediamine)] sheet was employed to perform the wet treatment by using ethylenediamine and hydrazine, respectively, as the base. The results of treatment was evaluated according to the elemental analysis (atomic ratio of O/N) by using XPS as well as the surface morphologies by using AFM and SEM. Furthermore, a copper layer was deposited onto the modified surface via the chemical plating. The adhesion strength between two moieties was assessed by the tape-peeling test. A large adhesion enhancement has been achieved when copper is plated on the modified surface of PI sheet. An added benefit of surface modification is that a uniform copper layer can be realized.
Polyimide Gels: a Novel Thermostable Polymer Network
(Abstract not yet available)
Development And Optimization of a Laser Carbonized Polyimide Film as a Sensor Substrate for an all Polymer Humidity Sensor
Kapton* and Upilex* polyimide films were studied as viable sensor substrates using a capacitive type humidity sensor design. An argon ion laser was used to pyrolize the Kapton* and Upilex* films to form raised, carbonized filaments. Using a graphics program and a set of computer controlled servo mirrors, an interdigitated circuit was formed on the surface of the polymer. This circuit was coated with a hygrosensitive polymer, HMPTAC (2-hydroxy-3-methacryloxypropyl trimethylammonium chloride), to form an all polymer humidity sensor. The sensor substrate was optimized for sensitivity by varying pyrolysis wavelength and energy density. Results show the polyimide based sensor performed as well as the most commonly used silica/gold and alumina/gold sensor substrates.
1 .Material Science Laboratory, Mitsui Chemicals, Inc.
2.Functional Materials Laboratory, Mitsui Chemicals, Inc.
3.Mitsui Chemical Analysis and Consulting Service, Inc.
Dry Etching of Polyimide Film with NF3-O2 Plasma
Oxygen mixed with nitrogen trifluoride (NF3) was used for the gas source of the plasma etching as one of the methods to increase the etching rate of the polyimide (PI) film. In order to investigate the effects of NF3 addition, surfaces of the etched PI films were analyzed with various methods. The roughness of the etched PI surface with 30% NF3 / 70% O2 plasma was lower than that of surface etched using 100% O2 plasma. From the results of x-ray photoelectron spectroscopy (XPS), chemical bonding state of the etched PI surface with 30% NF3 / 70% O2 plasma was similar to that of the surface prepared using 100% O2 plasma rather than that of 30% NF3 / 70% O2 plasma. The results of FT-IR analyses showed that the part of deposition materials on the etched PI film is soluble in chloroform and it contains carbonyl and ether compounds. Furthermore, the etching products were analyzed using quadrupole mass spectroscopy (QMS) and gas chromatography. Main products were assumed to be H2O, HF, CO and CO2. In addition, CO/CO2 ratio seemed to be related to the etching rate which depends on the NF3 concentration.
Electrostatic Properties of Polyimide Langmuir-Blodgett Films in Electronic Tunneling Devices
Surface potential of polyimide Langmuir-Blodgett films deposited on various kinds of metal electrodes has been examined as a function of the number of deposited layers at a temperature between -100C to 150 C by means of the Kelvin-probe method. It was found that the surface potentials clearly depend on the number of deposited layers and kinds of metal electrodes, indicating the displacement of excess electronic charges from metal electrodes. A linear relationship between the saturated surface potentials and the number of deposited PI LB layers was obtained. These results were explained by assuming that the surface Fermi level of PI LB films and the Fermi level of metals coincident at the interface due to the displacement of electronic charges. In this paper, the spatial charge distribution and electronic density of states in various kinds of LB films were determined, and the electrostatic properties of PI LB films in electronic tunneling devices were discussed in conjunction of the current-voltage (I-V) and capacitance-voltage
Center for Advanced Functional Polymers/Polymer Research Institute, Department of Materials Science & Engineering, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang, 790-784 Korea
*Department of Chemistry
Synthesis of Novel Polyimides from Dianhydrides with Flexible Side Chains
In the last two decades a large number of aromatic polyimides have been prepared and commercialized in part. But most of them have been derived from various diamines with complex structures and relatively simple dianhydrides such as pyromellitic dianhydride and oxy-, carbonyl- or methylenedi(phthalic anhydride). Such results are understandable in that structure modification of a diamine is generally easier than that of a dianhydride. The structure modification of pyromellitic dianhydride is particularly difficult because its four positions on benzene ring are already occupied by four carbonyl groups. In the present work we will discuss the synthesis of poly(pyromellitimide)s and poly(octahydroanthracenetetracarboxdiimide)s with flexible n-alkyloxy or bis[4-(n-alkyloxy)phenyloxy] side substituents and their applications as liquid crystal aligning films which are highly interesting in TFT(thin film transistor)-LCD(liquid crystal display) technology.
1) Buryat State University, Ulan-Ude 670000, Smolina Str. 24a, RUSSIA.
2) Baikal Institute of Natural Management, Siberian Branch of the Russian Academy of Sciences, Ulan-Ude 670047, Sahyanovoy Str. 6, RUSSIA.
3) Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Lavrentyeva Pr. 9, RUSSIA.
Novel Pyrimidine Containing Polyaminobisitaconimides
The Michael addition reaction is known to produce both high molecular polymers and oligoimides. Bismaleimide resins based on the Michael addition reaction of bismaleimides and diamines are widely used as matrix resins for composites. However bisitaconimides, which are more reactive, then bismaleimides, have not been investigated concerning with Michael addition reaction. On the other hand pyrimidine ring included to the polymer chain is suggested to increase thermal stability of polyimides.
In this paper the synthesis and characterization of novel pyrimidine containing polyaminobisitaconimides would be reported. The model compound was prepared via reaction of N-phenylitaconimide with aniline and was characterized by conventional measurements. The polymers were prepared from the reaction of pyrimidine containing bisitaconimides with various aromatic diamines. The effect of the temperature, catalysts and reaction time on the inherent viscosity and thermal stability of resulted polymers would be discussed.
Fullerene-doped P-conjugate Organic Materials Based on Polyimide: Nonlinear Optical Properties
Among photosensitive materials, fullerene-doped p-conjugate organic systems based on polyimide, 2-cyclooctylamino-5-nitropyridine, etc occupy a special place due to their large optical nonlinearities. In the present paper the fullerene sensitisation was made to reveal the nonlinear optical properties of polyimide materials. The 2-3 µm thick structures were doped with fullerenes C60 and C70. It was established, when fullerenes were introduced in the organic matrix, the diffraction efficiency increased drastically. The sensitisation resulted in a larger increase in the optical absorption at the laser wavelength of 532 nm, in a conformation transformation of organic chain and in a laser-induced photorefractive effect in them. Using dynamic hologram technique, the drastic change of refractive index Dni was observed and the nonlinear coefficients n2 and c(3) were estimated. The results were compared with those for silicon. The fullerene-doped systems could be applied for optical limiting at the incident laser energy density of more than 3 J cm-2. The reverse saturable absorption mechanism, the Förster mechanism, reinforcement of the donor-acceptor interaction due to the charge transfer complex formation, as well as an enhancement in the laser induced refractive index should be included to consider the optical limiting peculiarities in the fullerene-doped polyimide.
Fullerene-doped PDLC for Nonlinear Optical Application
Optical limiting and holographic recording peculiarities in the p-conjugated organic fullerene-doped PDLC systems based on the polyimide 6B, 2-cyclooctylamino-5-nitropyridine, and N-(4-nitrophenyl)-(L)-prolinol have been investigated in the nano-, pico-, and femtosecond regions. It has been established that fullerene-doped PDLC systems could be applied for optical limiting at the incident laser energy density of more than 0.3-0.4 J cm-2. It has been mentioned that the reverse saturable absorption mechanism, free-carrier absorption, LC reorientation effect, and scattering have been discussed to explain the OL in the fullerene-doped PDLC structures. Moreover, the spectral features, the reinforcement of donor-acceptor interaction, as well as the Förster mechanism should be included in this consideration.
It has been established that fullerene-doped PDLC structures can be used for hologram recording. The laser-induced refractive index has been estimated in the systems studied. The large laser-induced change in refractive index influences the OL effect in PDLCs based on these systems and predicts the large increase in nonlinear coefficient n2. Therefore, it gives an opportunity to apply these systems for conversion and modulation of laser radiation.
Polybenzobisthiazoles- Critical Issues in its Performance & Properties
Since late 1970s the Air Force Materials Laboratory Wright Patterson Air Force has had a energetic program in liquid crystalline rigid-rod polymers. As part of continuing efforts many academic and industrial organizations throughout the world are actively engaged in structural modification of rigid-rod benzazole polymers (PBX), specifically poly (benzobisthiazole-1, 4-phenylene) (PBZT), poly (benzobisimidazole-1, 4-phenylene) (PBZI), and poly (benzobisoxazole-1, 4-phenylene) (PBZO) with a view toward new multifunctional materials. The compressive strength of high performance polymeric fibres is much lower than their tensile strength values. To date reported compressive strength of M -5 fibre is highest among all polymeric materials (bulk or fibre). For comparison, the compressive strength of Kevlar and PBZT fibres is 400 MPa and 200 MPa, respectively.
The purpose here is not only to present a review but also rather to describe the relatively recent research advances with regard to the synthetic methods and approaches that have been utilized to enhance the compressive properties of PBZT fibres. In doing this some of the synthetic modifications and properties of the polymers so derived has been described and new physico-chemical approaches have been discussed.
Synthesis and Investigation of Poly(benzotriazolimides)
Heterocyclic nitrogen-containing, thermostable polymers prepared by the migrational copolymerization of bis(imides) of unsaturated acids and bis(phenols), bis(mercaptans), diamines and other bisnucleophilic agents are of great interest due to their higt performance characteristics. The aim of this work was to study the synthesis of oligo- and poly(benzotriazoles) by the migrational copolymerization of bis(bezotriazoles) and bis(maleimides). To model the process of polymer formation, we studied the addition of 1,2,3-benzotriazole to N-phenylmaleimide. The results obtained in the synthesis of the model compound allowed us to realize the process of polymer formation, starting from 5,5-bis(benzotriazolemethane) and 4,4-diphenylmethanebis(maleimide). Linear poly(benzotriazoles) were synthesized by the migrational copolymerization of equimolar amounts monomers, while three-dimensional crosslinked polymers formed when bis(maleimide) was in excess. The effect of temperature, the duration of synthesis, and the initial concentration of monomerson the viscosity reduced values of polymer solutions in N-methylpyrrolidone were studied, and the optimal conditions for the synthesis of polymers were established. Molding materials with good mechanical properties were obtained from oligomers synthesized with excess bis(maleimide). As evidenced by dynamic TGA, the temperature corresponding to the onset of degradation of linear and crosslinked polymers lies in the intervals between 360-380 and 400-410 C, respectively.
The Thermal Stabilities of Polyamidobenzimidazoles
The purpose of the current investigation is to analyze dependence of polyamidobenzimidazoles thermostability on the structure of the chemical units inthe macromolecular chain. Polyamidobenzimidazoles obtained on the basis of aromatetraamines, diphenyl ethers of aroma dicarbonic acids and caprolactum at a differetn mole ratio of initial monomers have been synthesized by a well-known method [1]. Common patters of the destruction processes of polyamidobenzimidazoles have been considered, using methods of thermal analysis along with IR spectroscopy and gas chromatography. Kinetic and physical chemical investigations of polyamidobenzimidazoles carried out reveal high thermal characteristics, depending upon the structure of the elementary unit and molar share of the initial monomers.
1. F.F.Izineev, V.V.Korshak, Z.P.Mazurevskaya. High molecular
compounds, 1986. V. 28, p. 489.
Instituto de Investigaciones en Materiales, UNAM, Circuito Exterior s/n, C.U. Apdo. Postal 70-360 Delegación Coyoacan, 04510 México, D.F.
Polymer Proton Exchange Membranes for Fuel Cell Application
Rapid advances of fuel cell technologies for power generation and transportation have created an increasing demand for novel high-performance polymeric materials for proton-exchange membranes (PEM). Fuel cells of this type have been considered as a promising alternative energy source because of their high efficiency at low temperatures, ease of construction, and low environmental impact. However, further progress in this area has been restricted by the insufficient performance of the conventional PEM's based on the perfluorosulphonic polymers such as NafionÒ, FlemionÒ, etc. These resins still remain the only commercially available polymeric electrolytes for PEMFC. Their service parameters maintain on an acceptable level up to 75-80ºC but above this temperature dehumidification of the hydrophobic perfluorinated matrix causes a dramatic decrease in the proton conductivity. Another important drawback is related to the inability of these membranes for the use in the direct methanol fuel cell (DMFC), considered as an attractive option for the automotive industry, due to their high permeability for methanol and water. The above are the major reasons stimulating intensive research and development of novel polymer electrolytes with operating temperatures in the range 80-200ºC and barrier properties adequate for DMFC. Different approaches have been used to meet these requirements, including: graft-modification and controlled crosslinking of the perfluorosulphonate polyolefins to improve their water retention and chemical resistance; synthesis and characterization of novel proton conducting heteroaromatic polymers such as polyimides, polybenzimidazoles, polysulfones, PEEK, etc; and the development of hybrid organic/inorganic electrolytes. The present paper reviews recent advances and discusses comparatively the potential of these and other techniques for the development of novel high-performance proton exchange membranes for fuel cell application.
3255 S. Dearborn Street, Illinois Institute of Technology, Chicago, IL 60616
Synthesis and Properties of Polyimides and Related Polymers Containing [5]Helicene Moieties
(Abstract not yet available)
Synthesis and Characterisation Aspects of Innovative Polyimide Nanocomposites
(Abstract not yet available)
Amine-Quinone Polyimides -- High Temperature Polymers that Protect Metals Against Corrosion
(Abstract not yet available)
Small Molecules Sorption and Transport in Polyimides and Other High Tg Polymers
(Abstract not yet available)
Hidetoshi Kita, and Ken-ichi Okamoto; Faculty of Engineering, Yamaguchi University, Ube, Yamaguchi, 755-8611, JAPAN
Synthesis of Polyimides from Novel Sulfonated Diamines and Their Proton Conductivity
Sulfonated aromatic polymer membranes have been attracted much attention because of applications to polymer electrolyte fuel cells (PEFCs). Sulfonated copolyimides derived from 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTDA) with a commercially available sulfonated diamine such as 2,2'-benzidine disulfonic acid (BDSA) and non-sulfonated diamines have been developed as proton-conducting materials for PEFCs. However, they have not the high hydrolysis stability enough to be used at high temperatures and humidified state. In this presentation, various novel sulfonic-groups containing polyimides were synthesized from NTDA and novel sulfonated diamines, and their hydrolysis-stability and proton conductivity were investigated. Some of these polyimide membranes displayed excellent hydrolysis-stability and proton conductivity, and their PEFC properties are under study.
1) Institute for Problems in Mechanical Engineering, Saint-Petersbourg, Russia
2) Institute for Composite Materials, Erwin Schroedinger Str. 58, D-67663 Kaiserslautern, GERMANY
3) Institute of Macromolecular Compounds, Saint-Petersbourg, Russia
Structure and Tribology of Polyimide-Fullerene Composite Coatings
Polyimide-fullerene (PI-Fu) composites have been obtained by three synthetic routes: Fu introduction into PI precursors a) amine, b) anhydride (prior to acylation of amine with anhydride) and c) into initially synthesized polyamic acid (PAA). After formation of PAA-Fu solution the systems were imidized to form PI-Fu composite. The composite PI-Fu material was investigated in a form of thin films and coatings prepared by pouring PAA-Fu solution onto steel substrates with subsequent drying and imidization. The PI-Fu composite was found to have a heterogeneous structure with a size of heterogenieties ranging from nanometers to micron length scale. Infra-red spectrometry, scanning electron microscopy, wide angle X-Ray analysis, thermal desorbtion spectrometry and other structural methods were used to characterize the nature of the heterogeneous PI-Fu system and its responce to temperature conditions at the late stages of imidization reaction. The correlations between structural data and tribological properties of the PI-Fu composite coatings are discussed.
Synthesis of Phenolformaldehyde Containing Pendant Itaconamic Acid, Itaconimide and Poly [ N -Substituted ) Itaconimides ]
Ortho and meta aminophenols were allowed to react with itaconic anhydride forming N- ortho and N- meta hydroxyphenylitaconamic acid in good yields . The above substituted itaconamic acids Were allowed to react with formaldehyde in conditions similar to that of Novolac preparation ,and novol phenol formaldehyde resins were obtained having pendant itaconamicacids. Similarly, formaldehyde was allowed to react with N-ortho and N- meta hydroxyphenylitaconimides producing novol resins.Furthermore, theitacon vinyls of the pendant groups of itaconamic acids as well as their corresponding imides were polymerized free radically using AIBN as initiator,and crosslinked tough resins were obtained .
New Photoalignable Polyimides and Their Ability to Control Liquid-crystal Alignment
A series of new photoreactive moieties were synthesized, and incorporated into a high performance polymer as side chains. The polymers were soluble in common organic solvents, producing a good quality of thin films in spin- and bar-coating and subsequent drying process. Their photoreactivity to UV light was investigated by UV-exposure and UV-visible spectroscopy. A preferential photoalignment of polymer chains was achieved with a relatively low exposure dose of 0.25-0.5 J/cm2. The preferential alignment of polymer chains was confirmed by optical retardation measurement. With the polymer films, liquid-crystal cells were prepared and examined. A wide range of pretilt angle was achieved, depending on the side chain length of polymer as well as the exposure technique and exposure dose. In addition, structure and basic properties of the polymers were characterized in detail. [This work was supported in part by the Ministry of Industry & Energy and the Ministry of Science & Technology (G7 Project) and by the Center for Integrated Molecular Systems (KOSEF).]
1) A.N.Nesmeyanov Institute of Organo-Element Compounds, Russian Academy of Sciences, 28, Vavilov Str., Moscow, 117813, RUSSIA.
2) University of Akron, Akron, OH 44325-3909 USA
New Highly Phenylated Bis(phthalic) and Bis(naphthalic) Anhydrides and Polyimides Therefrom
New highly phenylated bis(phthalic) and bis(naphthalic) anhydrides containing carbonyl central group, were prepared by the interaction of 4,4'-bis(phenylglyoxalyl)-benzophenone with two-fold molar amount of 1,3-diphenylacetone bollowed with treatmebt of 4,4'-bis(2,3,5-triphenylcyclopentadien-1-on-4-yl)-benzophenone thus obtained with 4-(phenylethynyl-)naphthalic anhydride or maleic anhydride. New highly phenylated bis(phthalic) and bis(naphthalic) anhydrides thus obtained were interacted with different aromatic diamines under conditions of high temperature solution polycyclocondensation in phenolic solvents. Highly phenylated polyimides and polynaphthylimides prepared combined outstanding solubility in organic solvents and high thermal stability with high molecular weights and good film-forming properties. Mechannical, electrical and optical properties of the polyimides prepared were investigated.
Synthesis of Skeleton-linear Polyimides with Specified Spatial Structure
The results of synthesis of skeleton-linear polyimides by polymerization on Diels-Alder of bis-imides of 2,3,4,5-tetrachlorobicyclo [4,4,0]deca-2,4-diene-7,8-dicarboxylic acid with bis-maleicimides are discussed. It has been shown that by variation of configurations of articulated cycles of monomeric polycyclic anhydride and imide groups and conformations of six-membered rings it is possible to create stereoisomeric skeleton-linear polymeric structures. It has been established that the synthesized polyimides possess higher fire-resistance and better solubility and have maximum degree of imidization.
Investigation of Thermo-Mechanical Properties of Polyimide-Silica Endlinked Nano-composite System Prepared by In-situ Polymerization
(Abstract not yet available)
Highly-oriented Poly(p-phenylenepyromellitimide) Film by Novel Gel Drawing Technique.
Poly(p-phenylenepyromellitimide)(PPPI), is the simplest form of aromatic polyimide with completely rigid backbone structure. From this rigidity there has been enormous efforts on fabrication of PPPI film with expecting ultra-high modulus. However, all of trials ended up identifying PPPI as too brittle a material to apply any practical usages. One of the origins of brittleness of PPPI is in hydrolytic instability of precursor polyamic acid that is easily degraded by ambient moisture and water generated on imidization. Another one is in a coarse grained structure spontaneously developed by intrinsic high-crystallinity of PPPI, that may induce stress concentration by applied force. To break through these problems we propose new concept of fabrication technique; gel drawing. In this technique the highly swollen polyisoimide gel is used as precursor and subjected biaxial orientation by using gel drawing with keeping the swollen state. The oriented polyisoimide gel film is converted to tough polyimide film by heat treatment at above 350C. Finally obtained gel-drawn PPPI film has 20 Gpa of Young's Modulus with balanced orientation, exceeding any of currently commercialized plastic film.
Synthesis and Properties of Novel Fluorinated Polyimides
The synthesis and properties of phenylethynyl end-capped and non-endcapped polyimides derived from 4,4'-(2,2,2-trifluoro-1-phenylethylidene)diphthalic anhydride (3FDA) and various diamines will be addressed. The influence of molecular structure on complex viscosity, thermal properties, and dielectric constant will be discussed. In addition, molecular weight effects and structural changes of a NASA developed phenylethynyl end-capped imide oligomer, PETI-5, on viscosity and thermal properties will also be presented.
New Trends in High Performance Thermosetting Resins
(Abstract not yet available)
Polynadimides Obtained by Diels-alder Reactions
(Abstract not yet available)
1) Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg 199004, RUSSIA
2) Casali Institute of Applied Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, ISRAEL
Crystallization Morphology and Liquid Crystalline Textures in Aromatic Imide Oligomers and Their Blends withThermoplastic Semicrystalline Polyimide
There is a strong recent interest in obtaining of a new type of high-performance composites based on semicrystalline thermoplastic polyimides (PI). The physical and mechanical properties of such composites depend crucially on the crystallinity and morphology of the PI matrix. This study demonstrates the novel crystallization behaviour of a new semicrystalline PI (Tg = 198°C, Tm = 324°C) which can recrystallize from the melt by adding the low molecular weight oligoimides (OI). Morphology, phase transitions and mesomorphic liquid crystalline (LC) textures in different OI, PI and blends PI/OI under the variation of the processing conditions have been studied using scanning electron microscopy, wide angle X-ray diffraction, thermal analysis and polarized light microscopy of hot-stage controlled crystallization. It is found that in the process of thermal or chemical imidization, some OI undergo crystallization with the formation of one, two or three various crystalline modifications while only a semicrystalline structure can form in the pure PI. During cooling from their isotropic melts, OI and its blends of PI/OI underwent a monotropic LC transition to form a nematic-like phase or smectic A-like phase, followed by a transition to a more ordered structure. The pronounced acceleration of the crystallization was observed whenever this was preceded by LC formation, an effect pertaining within a wide temperature range. Changes in the LC textures and character of morphology, which affect on the mechanical properties of blends PI/OI in composites have been observed.
Humid Aging of Polyimide
The aim of this work is to study the behaviour of amorphous polyetherimide(PEI) at short and long term in a humid environment.
The study of humid aging of PEI in aqueous environment (neutral or acid solution, pH2) at 100, 170, 180°C shows the very good hydrolytic stability of this material, despite the presence of imide groups, sensitive to hydrolysis.
The detailed study of the physical interaction between the polyetherimide and water leads us to establish the characteristics of sorption : solubility and diffusivity. The water equilibrium concentration increases slightly with temperature from 1,39% (by weight) at 20°C to 1,50% at 100°C. The solubility coefficient,S , calculated from these data and the water vapor pressure, decreases with temperature. The calculated heat of dissolution Hs is close to -43 kJ mol-1 . The diffusion coefficient,D, varies from 1.10-12 m2.s-1 at 20°C to 16.10-12 m2.s-1 at 100°C. The apparent activation energy of diffusion ED and the heat of dissolution Hs of water in the polymer have opposite values(respectively, +43 and -42 kJ.mol-1). From this observation and a comparison of these data with water diffusion characteristics in other glassy polar polymers, it is hypothesized that the transport rate of water is kinetically controlled by the dissociation of water-polymer complexes.
The consequences of water absorption on the physical and mechanical properties are studied. Despite a slight decrease of the yield stress linked to plasticization, the ductility decreases indicating that water absorption favors a new, presumably localized, yielding process
Application of Polyimides for the Development of Thin Film Solar Cells
There is a recent interest to develop lightweight and flexible solar cells for space and terrestrial applications. Polycrystalline thin film solar cells of CdTe and Cu(In,Ga)Se2 (called CIGS) semiconductors are potentially important because of their low cost, high efficiency and stable performance.
CIGS and CdTe thin film solar cells are developed by deposition of multilayer stacks on the polyimide substrates. Commercially available Kapton and Upilex sheets, as well as spin coated polyimide films are used as substrates. Thin layers of different thermal expansion coefficient are deposited by sputtering or thermal evaporation methods at temperatures of up to 450 °C. The thermo-mechanical, chemical and optical properties of the polyimide substrates are important for the growth and performance of solar cells. Lightweight and flexible solar cells with record conversion efficiencies of 11% and 12.8% have been obtained for CdTe and CIGS, respectively. Various applications of flexible solar cells and the requirement of the high temperature polyimides in solar cells will be discussed
Effect of Structure on Thermal Behaviour of Bisitaconimide Resins
Many addition polyimides such as bismaleimides, bisnadimides have been extensively investigated in the past. These resins are currently being used as
matrix resins for advanced fibre reinforced composite materials which find applications in the aerospace, defence and electronics industries. As one of the thermoset materials, these polymers offer superior thermal oxidative stability and better retention of properties in hot wet environments than the
conventional epoxy resins.
The potential of bisitaconimide resins, which cure at lower temperatures than bismaleimide or bisnadimide resins and yield a cross-linked network with thermal stability comparable to other types of addition polyimides has not been fully explored. In this paper, recent studieson synthesis and characterisation of novel itaconimide resins would be described . The effect of structure on thermal behaviour would be discussed.
Devlopment of Polyimide Blends and Study of Electrical Properties of Plastics on their Composition.
Investigations of relationship of polyamide acides with different electromagnetic fields showed the process of polyamide acids imidizaton occurs faster under the influence of rather powerful super high frequency electromagnite field than under thermical or chemical imidation. This fact provides new opportunities of obtaining multicomponent thin disperse polyimide blends.
Polyimide press powders of super thin dispersion are produced with the help of super high frequency electromagnite fields. It is impossible to produce them using traditional methods. Optimum regimes of irradiation of polyamide acids have been determined. This forepolymer of definite degree of imidation containig certain quantity of reaction groups can be produced. As a result of the imidation reaction partly imidate polyamide acid turns unsoluble in organic solutions. Sediment of power of great dispersion is formed. IR-spectroscopy is used to control the depth of polyamide acid transformation into polyimide. No chemical reagents able to produce any byprocess are used for the powder segmentation.
Polyamide acid solution was mixed with the solution of other polymers in the same solvent to produce double or multiple component polyimide blends.
Polyamide acid transfers to polyimide. Macromolecules turninig unsoluble
roll up into globules capsulating fragments of macromolecules of other polymers.
Multicomponent composition powder of thin dispersion on polyimide basis with high degree of uniform of polymer components has been produced. The investigation of electric properties of the samples produced by hot pressing of the composed powders proved the obtained plastics to be not only inferior to film materials but not obtain a number of advantages of volume samples.
Polyamic Acids and its Ionic Salt Solution: Synthesis, Characterization and its Storage Stability Study
Two series of co-polyamic acids containing various mole percent of ortho-Tolidine (o-TD) and 1,3-bis(3-aminopropyl) tetramethyl disiloxane (Si-Dam) were prepared by reacting with 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA) or 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) in N-Methyl Pyrrolidinone (NMP) solvent at room temperature. Subsequently, using these Co-PAAs, two series each of ionic bond type photodefinable co-polyamic acid (Co-PDPAA), ie. ionic salts, were made from N,N-diethyl ethyl methacrylate (DEEM) and N,N-dimethyl ethyl methacrylate (DMEM) respectively.
Storage stability of these solutions at room temperature was monitored for a period of one month by GPC, Potentiometry and Viscometry. Bulk viscosity, inherent viscosity, acid number and molecular weight decreased drastically as the storage time increased.
Rheological behaviour of Co-PAA and Co-PDPAA in solution was also investigated as a function of Shear rate and temperature. At room temperature, all co-polymer solutions, showed shear thinning behaviour in the shear rate range of 3.07 to 38.4 s-1. The temperature dependence of bulk viscosity followed the Arrhenius equation. Activation energy of viscous flow of BTDA based Co-PAA and Co-PDPAA are in the range of 25 - 27 and 22 - 26 kJ/mol respectively, where as BPDA based Co-PAA and Co-PDPAA are in the range of 12-28 and 19-33 kJ/mol respectively. Both activation energy of viscous flow and ln [A] decreased with increase in Si-Dam content in Co-PAA and Co-PDPAA series. For a given composition, activation energy of viscous flow is comparable for DMEM and DEEM based Co-PDPAA.
Thermal stability of precipitated solids of Co-PAA and Co-PDPAA were investigated using thermogravimetric analyzer (TGA). They showed two-step weight loss in air atmosphere. First step was due to imidization and second step was due to degradation. Activation energy for thermal degradation was determined using Coats-Redfern and Chang methods. The activation energy determined by both methods is comparable.
Polyimide/Polystyrene Nanocomposite Films as Membranes for Gas Separation and Precursors for Polyimide Nanofoams*
A method for the preparation of polyimide nanofoams with high thermal stability, which can be used as dielectric layers in microelectronics, has been presented in this paper. Polystyrene (PS) and poly[styrene-co-(4-vinyl-pyridine)] (PSVP) nano-particles were prepared by emulsion polymerization. The dimension of these particles is 60 to 80nm. PMDA-ODA nanocomposite films with various contents of PS and PSVP were obtained by in-situ condensation polymerization in the presence of the nanoparticles, casting of polyamic acid solution containing the nanoparticles, and imidization. The distribution of the nanoparticles in the films and the morphology of the composite films were characterized by TEM. Relative homogenous distributions were observed for the polyimide/PSVP nanocomposites, which can be ascribed to the formation of polyamic acid amine salts between pyridinyl and carboxyl. The gas transport properties of CO2, O2, N2, and CH4 for these nanocomposite films were investigated. It was found that the film containing 10% PS nanoparticles show both high gas permeability and high permselectivity. Upon a thermal treatment, the thermally unstable nanoparticles undergo thermolysis, leaving pores where the size and shape are dictated by the initial nanoparticle morphology. The resultant foams were characterized by TEM, DSC, TG, density measurements and dielectric constant measurements respectively. The results showed that nanofoams with high thermal stability and low dielectric constant approaching 2.0 could be prepared using polyimide nanocomposite approach.
*: This work was supported by the National Natural Science Foundation of China (Grant Nos. 59703005)
Fluorinated Polyimides for Microelectronic Applications
Soluble fluorinated polyimides have been prepared derived from fluorine containing aromatic diamines, 1,4-bis (4-amino-2-tritluoromethylphenoxy) benzene (p-6FAPB), 1,3-bis (4-amino-2-trifluoromethyl phenoxy) benzene (m-6FAPB), 1,4 (4'-aminophenoxy)-2-(3'-trifluoro-methylphenyl) benzene (TFPPA), 2,4-diamino-3'trifluoromethylazobenzene (TFDA), 2,4-diamnno-1-(4'- trifluoro methyl) phenoxy aniline (TFPA), 3,5-diamino-l-(4'-trifluoromethyl)-phenoxy benzamide (TFPB) with various aromatic tctracarboxylic dianhydrides, including 4, 4'-oxydiphthalic anhydride (QDPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) and 4,4'-hexafluoro-isopropylidenc diphthalic anhydride (6FDA) by the procedure of onestep high temperature solution polycondensation, for microelectronics applications. The polyimides could easily dissolve in common organic solvents to afford homogeneous and stable solution with solid content of as high as 15-20%. Strong, tough and flexible polymer films (or coatings) could be fabricated by casting the polyimide solutions followed by thermally baking at temperature of X200 C to remove the free solvents. The polyimide materials show exceptional thermal and thermal-oxidative stability with onset decomposition temperature of >550'C for aromatic polyimides and >430'C for send-aromatic polyimides in N2. Low dielectric constant and disspation factor were observed due to the presence of fluorinecontaining substituents. The excellent combined features of the polyimides ensure them great potential candidates for microelectronics applications.
1) Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg 199004, RUSSIA
2) Casali Institute of Applied Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, ISRAEL
Semicrystalline Polyimides for Advanced Composites
New semicrystalline polyimides, designated for matrices in carbon fiber reinforced composites (CFRC) were developed. A specific advantage of the proposed polyimides is their ability to crystallization from the melt, therein retaining their crystallinity through the manufacturing process. The use of semicrystalline polyimides for a CFRP favors an increase in its thermal stability by about 100° over that of completely amorphous polyimides. The generation of crystallinity after melting, referred to as recrystallization, is investigated here as affected by blending of the polyimides with 5-10% by weight oligoimides of similar chemical structure. Based on thermal analysis and enthalpy measurements, comparative X-ray diffraction analyses and polarized light microscopy of hot-stage controlled crystallization the recrystallization ability is determined for different oligoimides. It is found that in some cases the addition of oligoimides, both amorphous and crystalline, results in complete recrystallization. It is suggested that the main contribution of the oligoimides is through plasticization, allowing segmental chain mobility during crystallization, and not via nucleation. A similar effect is obtained by lowering the molecular weight of the polyimide; this, however, generates mechanical property reduction, rendering the polyimide irrelevant to composite materials. It is shown that crystallization is also enhanced by carbon fibers, serving as a nucleating agent and generating trans crystallization.