ABSTRACTS
The following is a list of the abstracts for papers which will be presented in THE 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.)
** National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi-110012, India
Effect of Doping on the Thermal Stability and Electrical Conductivity of Polyaniline
The field of conducting polymers has surfaced as a viable option to replace existing conventional polymers for various technological applications due to their inherent ab!ility of control over a wide range of conductivity from insulating, semi-conducting and conducting regimes by a simple process of doping. In this regard, polyanilline (PAN) family of polymers offer renewed interest due to their excellent environmental stabi!lity, low cost monomer and high yield of polymerization, however, a complete characterization of their thermal, electrical, dielectric and structural properties is lacking thereby prohibiting their use in a variety of applications. The present report is a c!omprehensive study of polyaniline doped with sulphuric acid as a function of doping level. Dc conductivity and dielectric constant data have been measured as a function of doping level. The dc conductivity data show an i!ncrease in conductivity as the doping level is increased. The thermal behavior of undoped and doped PAN samples has been analyzed using thermal gravimetric analysis and differential scanning calorimetry techniques in order to understand the effect of dopant! on the thermal characteristics of PAN.
* Address for correspondence : Department of Physics, Gargi College, Siri Fort Road, New Delhi 110049, India.
(MUST PRESENT ON MONDAY NOV. 29)
Development of Some Metal-Containing Polyimides For Optoelectronic Applications
The chemistry, electrochemical properties, and photophysics of bis(2,2':6'2"-terpyridine) ruthenium (II) [Ru(tpy)2]2+ complex and its derivatives have been studied extensively owing to their interesting excited states properties. The [Ru(tpy)2]2+-typed complexes exhibit a characteristic spin allowed d- * metal-to-ligand charge transfer (MLCT) transitions and are well known photosensitizers. They are widely used as the key components in the studies of photoinduced electron transfer processes. We have been exploring the feasibility of incorporating different types of ruthenium bipyridyl or terpyridyl complexes into different polymer systems. One of our main objectives is to study the effect of transition metal complexes to the optoelectronic properties of polymers.
Here, we describe the synthesis and properties of a new series of novel aromatic polyimides functionalized with the bis(2,2':6',2"-terpyridine) ruthenium (II) complex. Different physical properties such as thermal stability, photoconductivity, luminescence, and charge transport properties were investigated. The absorption of the polymers at 500 nm was strongly enhanced by the ruthenium complex. As a result, the photosensitivity of the polymers in the visible region is increased, as can be seen from the increase in photoconductivity. The electron and hole carrier mobilities of polyimides are of the order of 10-4 cm2 V-1 s-1, which suggests that the electron-withdrawing diimide moieties play a role in the charge transport process. Emission from the metal complexes and charge transfer states were observed in these polymers. The polyimides also exhibited electroluminescent behavior when the polymer films were fabricated into single layered light emitting diodes. The external quantum efficiency and maximum luminance of the devices were found to be 0.1 % and 120 cd/m2, respectively.
i. Sauvage, J. P.; Collin, J. P.; Chambron, J. C.; Guillerez, S.; Coudret, C.; Balzani, V.; Barigelletti, F.; De Cola, L.; Flamigni, L. Chem. Rev., 94, 993 (1994)
ii. Ng, W. Y.; Gong, X.; Chan, W. K. Chem. Mater. 11, 1165 (1999)
Development of Bisitaconimide Psuedothermoplastic Resin
Bisitaconimide resins for making laminates have been developed and studied in detail by Rao et al (1989). They have reported the reaction of itaconic anhydride (IA) and methylene dianiline (MDA) giving bisitaconamic acid (BIA). During the imidization of BIA in dimethyl formamide (DMF) solvent at 125-130oC, they observed that polymerisation occurs simultaneously.
With this background information, in the present work, the polymerisation was allowed to increase significantly, which was monitored by measuring the acid value and inherent viscosity of the resin. When the inherent viscosity increased to desired level, chain extender (MDA) was added. This resulted in a very viscous mass. This viscous mass was washed thoroughly with water and the powder dried. This resin is referred to as ABRON-MP 45. ABRON-MP 45 was then characterised by IR and DSC.
ABRON-MP 45 was used for compression molding in a conventional hydraulic press. Application of heat and pressure in steps gave compression-molded billets. The effect of various fillers on the properties of the billets was studied. Some properties such as compressive strength, bulk density and hardness were determined.
Reference:
Rao, K.V.C., Vijayan, T.N., Bisht, M.M.S. and Nema, S.K., Polymers and composites - Recent Trends, Oxford and IBH Publishing Co., 156, 1989.
# Author to whom correspondence may be addressed
1 DuPont Company, Experimental Station E302/126C, PO Box 80302, Wilmington, DE 19880
2 GE Company, GE Plastics, 1 LEXAN Lane, Mt.Vernon, IN 47620
3 University of Massachusetts Amherst, Polymer Science and Engineering Department, Amherst, MA 01003
Determination of Orthotropic Elasticity Coefficients and Coefficients of Thermal Expansion for Polyimide Coatings
Polyimide coatings are commonly found as dielectric interlayers in high density multi-chip module packages. Orthotropic linear elasticity theory has been applied as the basis to characterize several thin polyimides including novel fluorinated polyimides. Using a combination of techniques which include vibrational holographic interferometry, high pressure gas dilatometry, tensile testing, thermomechanical analysis, pressure-volume-temperature apparatus, and torsional pendulum, the in-plane and out-of-plane elasticity coefficients and coefficients of thermal expansion were determined. Complete knowledge of these properties can be important for proper material selection and reliability prediction of complex microelectronic devices using finite element analysis.
Demitrios S. Papadopoulos, DeNise Hardy-Green, University of Akron, Akron, OH 44325
Synthesis and Characterization of a High Tg Polyimide (DMBZ-15)
A high Tg thermosetting polyimide (DMBZ-15) was developed by replacing methylene dianline (MDA) in PMR-15 with 2,2'-dimethylbenzidine (DMBZ). DMBZ-15 Polyimide neat resin and carbon fiber (T650-35) composites were fabricated from a formulation of 3,3', 4,4'-benzophenone tetracarboxylic acid, dimethyl ester (BTDE) and 2,2'-dimethylbenzidine (DMBZ) with nadic ester (NE) as the endcap. DMBZ-15 displays a higher glass transition temperature (Tg = 414 C) than that of PMR-15 (Tg = 345 C), and thus retaining better mechanical properties for brief exposure above the glass transition temperature. The thermal and physical properties of the DMBZ-15 polyimide will be compared to that of PMR-15. Furthermore, the thermo-oxidative degradation products and profile of DMBZ-15 will also be discussed.
The Photochemistry and Photophysics of Polyimides. The State of the Art?
Polyimides and related model compounds undergo a number of photochemical reactions that are of intrinsic interest to photochemists and photophysicists. The photochemistry of polyimides is also of significant technological interest because polymer photoreactivity sometimes should be minimized, for example, in environments where a polyimide used as a protective coating is exposed to light, and sometimes needs to be maximized, in applications, such as in photoresists, where a high sensitivity to light is desirable! There is an increasing degree of complexity in photochemical and photophysical behavior as one moves from simple model compounds such as phthalimides, to 'isolated' polyimide chains in solution, to the pure polymers. In the latter case, the full range of possible processes from reaction or decay of an isolated excited chromophore, to interactions between chromophores on the same or different polymer chains, must be considered. In this paper, I will review our current understanding of the photochemistry and photophysics of polyimides and related model compounds and discuss our recent studies of the role of charge transfer states and triplet state self-quenching in phthalimide and polyimide photochemistry and photophysics.
A New Family of High-Temperature Aromatic Copolyester Thermosets
Early work on the aromatic copolyesters is briefly reviewed. This includes comments on the emergence of the field of liquid crystalline (LC) polyesters as well as the more recent elucidation of the sequence ordering in the (LC) copolyesters.
Recent progress on the development of a new family of thermosetting copolyesters which grew out of the original LC polyester work is described. This new system solves many of the shortcomings of the commercially available thermosets by providing a system which is stable in air at 350 C. One unique feature is that it represents the only thermosetting resin which can be recycled back to a reactive oligomer by using a high temperature interchain transersterification reaction (ITR) with controlled amounts of acetic acid. Another unusual characteristic is that coatings can be first cured and then the coatings consolidated at 300C to form a very strong adhesive bond through solid state ITR at the interface.
One important area of use for this new family of thermosetting polyesters is in the design of advanced Multi-chip Module Laminates as well as MEMs structures. In the first case approaches to improving performances, reliability and reducing cost are described. In the second case methods for modifying the polyester to either planarize or conform to surfaces are described. In addition use of this new resin to form extremely thin adhesive bonds at the submicron level are presented.
Tetracarboxylic Bisimide-lactam Ring-contraction; a Route to Polylactamimides - Novel Class of Polymers with Intramolecular Charge Transfer.
Six-membered ring dicarboxyimides were found to undergo unusual ring contraction followed by decarboxylation under mild basic conditions to produce lactamimides. In all cases only one imide ring is transformed leaving the second one unchanged 1). This novel reaction was studied theoretically, modified and adopted to the synthesis of polylactamimide-containing polymers.
First polylactamimide were synthesized by two different methods: 1. polycondensation of lactaimide-containing monomers2,3) and 2. bisimide-lactam ring contraction of six-membered polyimides 4) to produce amorphous polymers with strong luminescence (quantum yield>80%) and large Stokes shifts due to intramolecular charge transfer from lactam to imide moiety rendering them promising compounds for dye lasers. All-aromatic polylactamimides exhibited T10 up to 510 oC and third order non-linear optical susceptibility up to 10-10 esu.
REFERENCES
1.H. Langhals, P. Unold, Angew. Chem., Int. Ed. Engl. 34, 2234 (1995)
2 S. Fomine, L. Fomina, V. Garcia, and R. Gaviño Polymer, 39, 6415-6421 (1998)
3. L. Fomina, S. Fomine, P. Ponce Peña, T. Ogawa, L. Alexandrova and R. Gaviño. Macromolecular Chemistry and Physics 200, 239-245 (1999)
4. S. Fomine, L. Fomina, R. Arreola and J. Carlos Alonso Polymer 40 2051-2058 (1998).
# Centre for Polymer Science and Engineering (CPSE), Indian Institute of Technology, Delhi, New Delhi 110 016. India.
Cryotreatment- An Effective Technique for Enhancement of Abrasive Wear Performance of High Temperature Engineering Polymers
The increasing demands for high performance materials for operating in harsh operating conditions such as high speeds, loads and temperatures with superior properties call for either new materials or new formulations. Engineering polymers and composites are extensively used in wear situations dominated by various types of abrasive mechanisms. Various surface or bulk modification techniques have been successfully employed to enhance wear behavior of metals as well as nonmetals. In the case of metals, cryo-treatment is an emerging technique for improving wear resistance. The group has recently reported that the technique has potential to enhance the wear performance of various polymers and composites also. In this paper investigations on the influence of cryo-treatment on wear performance of a series of high performance engineering polymers such as Polyetheretherketone (PEEK) and its glass fibre (GF) and mineral filled composites, Polyphenylenesulphide (PPS), Polyethersulphone (PES), Polyvinylendifluoride (PVDF) and Polysulfone (PS) have been carried out. Ultrahighmolecular weight polyethylene (UHMWPE), the most abrasive wear resistant material was selected for reference. The selected materials were cryogenically treated at liquid nitrogen temperature for 24 hours and then brought back to room temperature at controlled heating rate. Abrasive wear performance was evaluated at ambient temperature on a pin-on-disc machine using Silicon Carbide (SiC) paper as a counterface in a single pass condition. Comparison of wear rates of treated and untreated samples under various loads revealed that this technique has potential to increase the wear resistance of the selected polymers and composites. The extent of improvement due to cryo-treatment on wear resistance depended on the type of the polymer. Changes in crystallinity and hardness were studied and correlated with observed wear behavior. SEM was used to examine the changes in morphology due to cryo-treatment.
Key words: Engineering polymers, Short fiber reinforcement, Abrasive wear resistance, Cryogenic treatment
Dynamic Mechanical Properties of Carbon-fiber-pmr-15 Polyimide Composites Containing Thermoplastic Polyimide Interphases
Carbon fibers were successfully coated with thermoplastic polyimide, TPI, interphases by an electrochemical process and subsequently impregnated with PMR-15 polyimide resin. The storage modulus of the composites increased with decreased thickness of the TPI interphase. However, the control composite showed lower storage modulus than the composites containing TPI interphases.
A plot of the tangent of the phase angle of the composites as a function of the test temperature, revealed that the control composites have two damping peaks at 230 and 488ûC, respectively. The low temperature damping peak was completely eliminated while maintaining a high glass transition temperature of about 388ûC, in composites containing thin TPI interphase, indicating that the thermomechanical stability of the composites can be improved.
(MUST BE IN JAPAN DEC. 2 - SCHEDULE EARLY)
Electrostatic Phenomena of Polyimide Langmuir-blodgett Films: Spacial Charge Distribution and Electronic Density of States at the Nanometric Interface
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 conventional 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 has been found. This result was 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 were determined, and we discovered the presence of electron acceptor-states at the interface. The model well supports our experimental results. Further we could explain theI-V characteristic of PI lB films sandwiched between metal electrodes, taking into account the interfacial electrostatic phenomena we discovered.
Synthesis of Hyperbranched Aromatic Polyamides and Polyimides from Abx Monomers
Dendritic macromolecules, such as dendrimers and hyperbranched polymers, deserve much attention for their unique physical and chemical properties. It is reported that both of them, usually amorphous, show good solubility in organic solvent, and low melt and solution viscosity. Hyperbranched polymers are generally prepared by self-polycondensation of ABx type monomers. Most of hyperbranched polymers have been prepared from AB2 type monomers due to its easy preparation of the monomer. In the beginning, AB2, AB4 and AB8 type monomers having the same repeating units were allowed to polymerize to form hyperbranched aromatic polyamides. Copolymerization of AB2 and AB type monomers were also carried out to investigate the influence of the incorporation of the branching unit on the property of the copolymer. Hyperbranched polyimides were prepared starting from an AB2 type monomer, isomeric mixture of 3,5-bis(4-aminophenoxy)diphenyl ether-3 $B!G (B,4 $B!G (B-dicarboxylic acid monomethyl ester via hyperbranched polyamic acid ester. Although hyperbranched polyimide with the amine terminal did not show good solubility in organic solvents, acetylation of the amine functional group afforded polyimide soluble in DMF, NMP, and DMSO. The acetamide terminal hyperbranched polyimide had Tg of 193 degree C and 10 % weight loss temperature of 470 degree C.
Thiazole Ring Based Poly(Ether imide)s
novel thiazole ring based poly(ether imide)s were synthesized by reacting the difluoro monomer viz. 1,1'-bis[4''-(p-fluorophenyl)-2''-thiazole]-4,4'-carbonyl diphthalimide with bisphenol monomers as hydroquinone, resourcinol, Bisphenol A, Bisphenol AF, 4,4'-dihydroxybiphenyl and 2,7-napthalenediol in NMP/Toluene solvent mixture in the presence of potassium carbonate. The difluoro monomer was synthesized by reacting 2-amino-4-(4'-fluorophenyl)thiazole (II) with benzene tetracarboxylic dianhydride (BTDA). II was synthesized by reacting fluroacetophenone (I) with Iodine in the presence of thiourea. (I) was obtained by reacting fluorobenzene with acetylchloride in the presence of AlCl3. The monomers were characterized by inherent viscosity which were in the range of 0.25-0.49dl/g. The thermal properties of polymers were studied by DSC and TGA measurement.
Synthesis of Flurorinated Polyimides
Fluorine containing moities register low electricalloss and high thermal stability. Incorporation of fluorine moities in polyimide structure was done to enhance thermal and electrical properties of this class of polymers.
4,4'-hexafluoro isopropylidine diphthalic dianhydride has been condensed ith 4,4-diamine diphenyl ether, 4,4'-diamino diphenylmethane & 4,4'-hexafluoro-isopropylidene using two different methods of synthesis. The first method is a one step process using DPS as solvent and imidazole as imidization reagent. The method gives polymer with inherent viscosity in the range of 0.3-0.4 dl/g. Another method using a two step process in which polyamic acid id formed in first step and imidization takes place in the second step. The amic aid formation takes place at 50 C and imidization at 100 C using NEt3 and Ac2O. The inherent viscosities are greater than 1.5 dl/g.
Strong bonds due to imide group have been observed in all the cases at 1726 and 718 cm-1. These polyimides are stable up to 500 C.
The Surface Properties of Polyimide Alignment Layers of Liquid Crystal Display
The surface properties of alignment layer of LCD was investigated on the perpendicularly rubbed LB film and spin-coated film by optical retardation, surface energy and FT-IR measurements. The population of polymer chains is dominantly oriented to the dipping and rubbing direction and estimated by optical retardation and FT-IR measurement at the number of layers. When 7 layers at 30 mN/m, a highly oriented polymer LB layer and the better alignment state of liquid crystal in cells were achieved. Polyimide LB films were rubbed in order to estimate the depth profile of rubbing, and the rubbing direction is perpendicular to the dipping direction. After rubbing, the orientation of polymer was measured by optical retardation and FT-IR method. It is observed that there exist a limiting number of layers where the influence of surfaces extends. The substrate surface freezes the polymer chains persistent to the rubbing force up to 7-9 layers, while the rubbing strength applied on the alignment polymer layers penetrates into about 30 layers. Th effect of surface treatments on the polymerized film will be also discussed.
Alexander A.Kuznetsov*, Sergei V. Lavrov**, Vladimir I.Berendyaev**, Boris V.Kotov** ; Institute of Synthetic Polymer Materials RAS*, Karpov Institute of Physical Chemistry, Moscow, Russia**
Molten Aromatic Carboxylic Acids : New Catalytic Media For One-pot Synthesis Of Thermoplastic Polyimides
Carboxylic acids are known as efficient catalists of cyclodehydratation (CD) reaction of polyamic acids. Resently, we have discovered that the melts of aromatic carboxylic acids at 130-1600C can be used as exellent media for synthesis of different structure high molecular weight fully cyclizied polyimides from corresponding diamines and tetracarboxylic acids dianhydrides [1,2]. The pecularity of the process is that the rate of CD of transient polyamic acid is very high under the conditions chosen, and chain growth proceeds via coupling reaction of fully cyclized oligomers with amino- and anhydride end group. So, the equlibrium of polycondensation is shifted continuously to the side of polymer. In a typical exeriment, the reaction of m-phenylene diamine (m-PDA) with bis-phenol A diphtalic anhydride (BPADA) takes about 1 hour to give fully-cyclized product (control by FTIR) with the logarithmic viscosity of 0,78 dl/g (DP=80-100). The reaction stops after consumption of all the reaction groups; it is sensitive to the exess of any functional groups. The molecular weight can be controlled efficiently by adding definite quantities of monofunctional components such as phtalic anhydride or anisidine in the reaction medium.
In addition we have found that the melts of aromatic carbxylic acids can be successfully used in direct polycondensation process from starting diamines and tetracarboxylic acids (instead of dianhyrides) to give high molecular weight fully cyclizied products too. The latter process proceeds with lower rate (fig.1, curve 2) via formation of corresponding dianhydrides in situ. The method offered showed high efficiency in a case of low reactive monomers such as 4,4-diaminodiphenylsulfone (DADPS), 2,6- diaminopiridine (DAP) . Moreover, a well-determined "smoothing" effect of the amine reactivity was observed, that is the difference in reactivity between
high and low reactive diamines in new polyimide synthesis is not so large as the same in the synthesis in amic solvents. This effect is probably connected with known effect of "equal basicity" of strong and weak bases in acid media.The method offered can be used for obtaining new statistical and block-copolymers.
1. Russian patent N 1809612 (1995)
2. Kuznetsov A.A., et al. , Macromol. Symposia. 1998. V.128. P. 203.
*) e-mail address: kuznets@ispm.ru
Chemical Compatibilization in Polyimide-polyimide Blends
Two-component polyetherimide-polyetherimide blends (PEI-1/PEI-2) possessing only one glass transition temperature Tg were obtained by consequent 2-step-1-pot catalytic synthesis of PEI-1 and PEI-2 in situ in the melt of benzoic acid at 140oC. (formulation 1, chemically-made). The monomer pairs were 1,6-hexa-methylenediamine and bisphenol A diphtalic anhydride (BPADA) for PEI-1 and m-phenylenediamine-BPADA for PEI-2. On cooling BA crystallized out in a separate phase and was easily evacuated by repeated washing with acetone. Polymer residue was dried in vacuo; then the samples were hot pressed at 2500C to give a polymer tablet. The thermal characteristics were measured by DSC at the temperature increase rate of 160C per minute. The mechanically blended PEI-1/PEI-2 formulations were also prepared by dissolution of separately synthezied PEI-1 and PEI-2 (each in presence of phtalic anhydryde as end capping agent) in a common solvent (melted BA) and by mixing for two hours at 1400C followed by evacuation and treatment of the polymer in a manner pointed above (formulation 2). The phase diagrams were constructed for all the formulations on the basis of DSC data. It is seen that in a case of mechanically- made formulation 2 (fig.1) a clear microphase separation occurs in a wide interval of PEI-1/PEI-2 ratios from 80:20 to 10 to 90, the Tg values for each phase being equal to 140 and 2100C. The phase diagram does not change for mechanically-made formulation using CHCl3 as common solvent. In a contrary, the experimental Tg points for chemically "in situ"-made formulations are placed just inside the region of phase separation of the mechanically-made mixtures and depend on the content. One Tg retained after 5 scans or after 2 hour annealing at 1700C. The Tg value for "in situ"-made 50:50 formulation (1600C) is equal to that of statistical 50:50 copolymer (synthesized in melted BA), though the length of glass transfer interval was much higher in a former case than in a latter (400C vs.200C) . By means of turbidimetry method, "in situ"-made formulation was shown to be rather diblock,
*) Institute of Synthetic Polymeric Matrials, RAS, Moscow
**) Karpov Institute of Physical Chemistry Moscow
***) Institute of Problem of Chemical Physics, RAS,Chernogolovka.
Self-catalysis in Cyclization Reaction of Model O-carboxyamides in Concentrated Solutions and in Solid Phase
The kinetics of cyclodehydratation (CD) reaction has been studied of two model o-carboxyamide compounds I and II in presence of N-methylpyrrolidone (N-MP) at 140-1500C in a region of I(II)/ N-MP weight ratios from 5:95 to 90:10. Compound I was N-phenylphtalamic acid in a form of higly crystalline powder with the Tm=1900C. Compound II was oligomeric polyamic acid (log =0,13 dl/g) obtained by polycondensation of on m-phenylenediamine (m-PDA) and 2,2-bis[(3,4-dicarboxyphenoxy) phenyl] propane dianhydride (BPADA) in CHCl3. II was evacuated as solvent-free amorphous powder possessing the glass transition at 1700C.A strongly expressed extremal dependence of relative CD rate (V0, conversion per cents per min.) on the I(II) content was found in both the systems, I and II. In a case of compound I, the V0 value was found to be as large as 16% conv.per min. at the I/ N-MP weight ratio of 80:20. This value is more than an order of magnitude higher than that for the diluted solutions or for solid-state CD process (0,4-0,6 per cents per min.). Analogous results were obtained in a case of compound II. These data are the evidence of self-catalytic regime of CD reaction in high concentrated solutions, the carboxydiamide playing the role of catalyst itself. Indeed, the model compounds I and II as well as high molecular polyamic acids can be considered as derivatives of benzoic acid which is a well-known catalyst of CD reaction. The most interesting fact is unusual role of the solvent in this process. In a region of I(II)/N-MP ratios between 100:0 and 80:20 the V0 increases with N-MP content. So, N-MP behaves as co-catalist in CD reaction. The position of the V0 maximum at the ratio of 80:20-weight corresponds to approximately 1:1 molar ratio of carboxyamide/N-MP. Appropriate kinetic scheme is offered to describe CD process in all the concentraion range from diluted solution to the solid state. It is based on the assumption that the ionic dissociation products of the o-carboxyamide/solvent 1:1 complex, but not o-caroxyamide itself, are the real catalytic species.
Analogeous strong CD acceleration effect was observed induced by addition of small quantity (1-3%) of water, dimethylacetamide or other polar solvents to solid model compounds I and II placed into the sealed glass ampoule, at 1500C. When the solid-state CD reaction of I was carried out in a sealed ampoule in the absence of any additive, the S-shaped CD kinetic curve was observed caused by the water released in situ in a course of CD reaction. Such behaviour and the presence of the induction period (till 20%conversion) are the typical features of autocatalysis by the reaction product. In an open ampoule acceleration effect does not occur due to vaporization of water. So, the small quantity of water in a system can induce the shift of CD process of PAA to the self-catalytic regime.
*) e-mail address: kuznets@ispm.ru
Acid-catalyzed Reactions In Polyimide Synthesis
Carboxylic acids are known as efficient catalists of cyclodehydratation (CD) reaction of polyamic acids. Resently, we have discovered that the melts of aromatic carboxylic acids at 130-1600C can be used as exellent media for synthesis of different structure high molecular weight fully cyclizied polyimides from corresponding diamines and tetracarboxylic acids dianhydrides The pecularity of the process is that the rate of CD of transient polyamic acid is very high under the conditions chosen, and chain growth proceeds via coupling reaction of fully cyclized oligomers with amino- and anhydride end group. So, the equlibrium of polycondensation is shifted continuously to the side of polymer. Aromatic carbxylic acids were successfully used also in "direct polycondensation" process from starting diamines and tetracarboxylic acids (instead of dianhyrides) to give high molecular weight fully cyclizied products too. Some unusual reactivity effects as well as effects of introducing co-solvent are discussed.
Examples of use of new synthesis in obtaining the different structure polyimides, copolyimides and block-copolyimides are given. Interesting application of new method is obtaining polyimide-polyimide blends with one glass transition temperature via consequent polyimide synthesis of two incompatible polyimides in situ.
New effect of self-catalysed CD reaction of olygomeric polyamic acids and model low molecular weight o-carboxyamides in high concentrated solutions in amic solvents is discovered. It is established that N-MP behaves as co-catalist in CD reaction. The position of the V0 maximum at the ratio of 80:20-weight corresponds to approximately 1:1 molar ratio of carboxyamide/N-MP. Appropriate kinetic scheme is offered to describe CD process in all the concentraion range from diluted solution to the solid state. It is based on the assumption that the ionic dissociation products of the o-carboxyamide/solvent 1:1 complex, but not o-caroxyamide itself, are the real catalytic species.
Analogeous strong CD acceleration effect was observed induced by addition of small quantity (1-3%) of water, dimethylacetamide or other polar solvents to solid model N-phenylphtalamic acid (PPA) placed into the sealed glass ampoule, at 1500C. When the solid-state CD reaction of PPA was carried out in a sealed ampoule in the absence of any additive, the S-shaped CD kinetic curve was observed caused by the water released in situ in a course of CD reaction. Such behaviour and the presence of the induction period (till 20%conversion) are the typical features of autocatalysis by the reaction product. In an open ampoule acceleration effect does not occur due to vaporization of water. So, the small quantity of water in a system can induce the shift of CD process of PAA to the self-catalytic regime.
*) e-mail address: kuznets@ispm.ru
Enikolopov Institute of Synthetic Polymeric Matrials RAS, Moscow,Russia
Karpov Institute of Physical Chemistry, Moscow,Russia
Novel Multiblock Copolyetherimides Containing Crystallizable Blocks
Marina Yu.Yablokova / Alexander A. Kuznetsov / Sergey N.Chvalun.
Enikolopov Institute of Synthetic Polymeric Matrials RAS, Moscow,Russia
Karpov Institute of Physical Chemistry, Moscow,Russia
By means of step-by-step chain growth in a course of consequent catalytic polycyclization in situ a series of novel multiblock-copolyeterimides (CPEI) were synthesized. They consist of two polyetherimide blocks A and B, block A being amorphous and soluble whereas B is crystallizable and non-soluble one. The degree of polymerization in block A was equal n= 5. The length of B block and the total B/A blocks ratio were variable, the latter was varied in interval from 0,1:0,9 to 0,8:0,2. At the B/A ratio 0,2 and lower CPEI obtained are soluble in CHCl3 and N-methylpyrrolidone. At B/A ratio 0,3 and more they are soluble only in 2SO4. The logarithmic viscosity of the samples in N-MP was equal to 0,3-0,35 dl/g. The structure of CPEI was studied by means of DSC and WAXS. Only one glass temperature was found in the region of B/A ratios from 0 to 0,2 which depended on the content of B block and increased from 220 to 2400C correspondingly. In a region of B/A ratios 0,3-0,4 a microphase segregation takes plase to give rise of two amorphous phases. The symptoms of formation crystall phase were not found. In a contrary, at the B/A ratio 0,5-0,8 clear reflexes corresponding to crystal structure of block B were observed on the WAXS pictures. The CPEI synthesized are of interest as thermostable laminates.
The work was partially supported by RFBR(Grant n 97-03-32740)
Chemistry and Properties of o-Hydroxy- and o-Amino-Substituted Polyimides
Ortho substituted polypyromellitimides were prepared from ortho bisaminophenols or tetraamines by means of either high temperature thermal treatment or low temperature catalytic imidization of poly(amic acid)s, PAAs. Cyclodehydration of the precursors with ortho OH or NH2 groups in the diamine moieties, in the presence of aliphatic anhydrides and tertiary amines, was accompanied by the formation of pendant acetate or acetamide groups, respectively. The substitutes had a notable effect on the thermal and chemical stability of the studied polyimides, and their mechanical properties and solubility. Above 350C o-hydroxy polyimides underwent a rearrangement to benzoxazoles. The temperature of this rearrangement decreased and a deeper conversion was attained when hydroxyl groups were replaced by acetates.
The model reaction of phthalic anhydride with 2-aminophenol or 1,2-phenylenediamine was used to elucidate the chemistry of the ortho substituted polyimides. It was found that N-(2-hydroxyphenyl)- and N-(2-aminophenyl)phthalamic acids cyclodehydrated spontaneously to form the corresponding imides at room temperature in aqueous media in the absence of any dehydration agent. A similar effect was observed for the o-hydroxy- and o-amino- polyimides. Treatment of N-(2-aminophenyl)phthalamic acid with trifluoroacetic anhydride led to the isoimide with an ortho trifluoacetate group in the diamine moiety. This thermodynamically unstable compound easily underwent secondary cyclization to yield a ladder 1,2-benzoylenebenzimidazole structure. This approach may lead to the further development of a novel low temperature route to ladder poly(aroylenebenzimidazole)s.
1 Instituto de Investigaciones en Materiales, UNAM, Apdo. Postal 70-360, Coyoacan, 04510, México D.F., E-mail: likhach@servidor.unam.mx
2 Karpov Institute of Physical Chemistry, Voronstsovo Pole, 10, Moscow, Russia, 103064, E-mail: chvalun@cc.nifhi.ac.ru
Poly(4,4'-diphenylene)pyromellitimide in Highly Oriented State
Highly oriented films of poly(4,4'-diphenylene)pyromellitimide were obtained via cold drawing of precursor poly(amic acid), PAA, followed by either thermal or chemical cyclodehydration, or drawing of the final polyimide that resulted from the low temperature catalytic imidization of the isotropic precursor. A drawing ratio as high as 80-100% was attained for all of these orientation techniques. The obtained samples were compared in terms of their mechanical properties, chemical and supramolecular structure. It was found that the cyclodehydration of the drawn PAA occurs at a significantly lower rate than the imidization of the isotropic samples. This may be due to the lower mobility of the macrochains in the highly oriented state. The WAXD study revealed notable differences in the identity periods calculated from various (00l) reflections. This has been explained by a heterophase model of the polymer structure comprised of highly ordered crystalline domains and a less ordered phase containing chemical defects. The volume fractions of these phases have been quantitatively estimated from the azimuthal distribution of intensity I(1/2) of different reflections (00l). The obtained values correlated well with the microscopic density and mechanical properties of the films.
Novel Approaches to Solubilizing Polyimides Without Sacrificing Thermal Properties
Polyimides with enhanced solubility have been synthesized from sterically hindered diamines having one or more methyl groups ortho to the imide nitrogen. Medium to high molecular weight polyimides with high Tg's ranged from 252 to 398 C and thermal stability up to 400 C in both air and N2 were obtained. Extended diamines with substitution ortho to the internal ether linkages were successfully synthesized: 1,4-bis(4-aminophenoxy)trimethylbenzene (TMBDA) and 1,4-bis(4-aminophenoxy)-2,5-di-t-butylbenzene (DTBDA). Soluble polyamides with high Tg's (237-305 °C), good thermal stability and moderate to high molecular weights were synthesized from these diamines. Polyimides were synthesized from TMBDA with good thermal-oxidative stability and high Tg values (235-300 °C) from flexible dianhydrides and with no detectable Tg's with rigid dianhydrides. No significant enhancement in solubility was observed. Aromatic polyimides with aliphatic cardo unit were synthesized from novel diamine 4,4-bis(p-aminophenoxymethyl)-1-cyclohexene (CHEDA). Most CHEDA polyimides were soluble with relatively high molecular weights. Tg's were in the range of 190 to 250 °C with no significant weight losses below 450 °C in N2. Utilization of pendant double bond for post-polymerization modifications was investigated through epoxidation and reaction with bromine. New aromatic poly(amide-imide)s (PAI) were prepared from commercially available materials in one-pot by the triphenyl phosphite-activated polymerization of diimine-dicarboxylic acids and aromatic diamines. All of the PAIs showed good thermal stability and moderate solubility in organic solvents and could be cast into tough, transparent films.
School of Polymer Science and Engineering, Polymers and High Performance Materials, University of Southern Mississippi, Hattiesburg, Mississippi 39406-0076
Thermal Conversion of Hydroxy-containing Imides to Benzoxazoles: Polymer and Model Compound Study
A series of hydroxy-containing polyimides, containing pendent hydroxyl groups ortho to the heterocyclic imide nitrogen, were prepared via the solution condensation of aromatic dianhydrides with bisaminophenols. The polyimides were found to undergo thermal conversion to polybenzoxazoles upon heating between 350 and 500 oC under nitrogen or vacuum. The thermal conversion was accompanied by loss of carbon dioxide. No other volatile by-products were detected by IR or NMR. Structures were confirmed by IR, solid-state NMR and elemental analysis. Polybenzoxazole films, obtained by the thermolysis of solvent cast poly(amic acid) or polyimide solutions, displayed excellent solvent resistance and good thermal stability. Insolubility of the polybenzoxazoles in all solvents tested indicates possible crosslinking. No crystallinity was observed by x-ray diffraction. Due to the insolubility of the resulting polybenzoxazoles, model compound reactions were also investigated. In the vapor phase at 400 °C, N-(2-hydroxyphenyl)phthalimide underwent intramolecular thermal conversion to 2-phenyl-benzoxazole in 83% yield, emulating the polyimide reactions. Thermal conversion of N-(2-hydroxyphenyl)-phthalimide in the melt at 400 °C resulted in the formation of intermolecular reaction products. The intermolecular reactions may be a source of possible crosslinks, which would explain the insolubility of the polybenzoxazoles.
Diels-Alder Trapping of Photochemically Generated Bisdienes with Bismaleimides - A New Approach to UV Curable Polyimides
(Abstract not yet available)
ArF Laser and Xe2* Excimer Lamp Induced Photochemical Fluorination of Polyimide Film
(BEFORE NOON ON 29TH)
The polyimide film has far superior in heat resistance, mechanical strength and chemical stability, and is widely used as aerospace materials and flexible printed circuit board. These excellent properties, on the other hand, make surface modification difficult. We have modified to hydrophilication photochemically onto polyimide film surface by using Xe2* excimer lamp and ArF excimer laser. But polyimide film is inferior to teflon in insulation and water repellency. Therefore, we tried fluorination of polyimide surface, by photochemical surface modification method. In this method, both of the water repellency and electrical insulation of the polyimide film were improved. Polyimide has imide group and benzene ring in molecules. C-H bond energy is 80.6kcal/mol. To modify polyimide surface photo-chemically, the C-H bond of polyimide was cut by UV photon(ArF excimer laser). As a substituent, to irradiate Xe2* excimer lamp, CF4 gases were photodissociated, and formed Cfn radicals. They are substituted to the C's dangling bonds of polyimide surface. By this treatment, the photo-exposed area of polyimide surface is selectively modified to be fluorination, whose affinity for water repellency improves. Experimentally, the polyimide film was placed in a reaction chamber, which was evacuated, purged of the residual gases by He and filled with CF4 gas. The gas pressure was changed from 0 to 200 Torr. By irradiating with the Xe2* excimer lamp (172nm, 165kcal) horizonally to photo-dissociate the CF4 gas. Simultaneously, Xe2* excimer lamp (193nm, 147kcal) vertically irradiated to the polyimide film surface. The contact angle with the water of a non-treatment polyimide with pure water was about 55 degrees. In this case of the CF4 gas of 100 Torr, Xe2* excimer lamp and 20mJ/cm2 ArF excimer laser of 3000 shots, the contact angle was 130 degrees.
Hydrophilic Treatment of Inner Porous PTFE Implant Devices for Intractable Glaucoma
*Department of Electrical Engineering Tokai University 1117 Kitakaname Hiratsuka Kanagawa 259-1292 JAPAN
** Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, University of Miami School of Medicine, 900 NW 17th Street, Miami, FL.
PTFE has several excellent characteristics such as environmental resistance, acid and alkali resistance, and repels water and oil. Porous PTFE is gas-permeable but not water permeable under normal atmospheric pressure. Because of these advanced characteristics, this material is used as a waterproof film. If the inside surface of the porous PTFE could be modified to possess hydrophilic properties, this material may be used as an aqueous separation film. As porous fluorocarbon polymer repels oil, fat and proteins in water solution cannot penetrate and only the water will separate. As porous PTFE has chemical resistance, it can be used as a film to separate vapor. Therefore, if we could substitute (O-H) on the inner surface of the porous PTFE, water osmotic pressure may be controlled. Intractable glaucoma results from hindrances in the eyeball aqueous humor circulation that allow the intraocular pressure to raise above normal physiological levels (>20mmHg). Pressure above 22mmHg may progressively damage the neuroretinal tissues resulting in a loss of visual field. If we could implant a suitable hydrophilic treated porous PTFE device between the inside and the outside of the eyeball, aqueous humor may drained automatically. By optimizing the implant shape, the intraocular pressure could be reduced to an acceptable physiological level (10-14mmHg). As fat and protein will not stick to the hydrophilic treated porous PTFE biomembrane, clogging of the device in situ will be minimized. In this study, the porous PTFE surfaces were made hydrophilic using a photochemical method. A fused silica glass window was placed on the porous PTFE surface and an alcohol aqueous solution was infiltrated into the thin gap between the glass window and porous PTFE surfaces. UV light was then projected onto the porous PTFE. The UV photons photodissociate the alcohol producing OH radicals. Simultaneously, the surfaces of the porous PTFE are also photodissociated producing carbon dangling bonds and F radical. The photodissociated OH radical is substituted to the C's dangling bond and therefore, the inner surface of the pores became hydrophilic. To render both outer surfaces hydrophilic, the film is turned around and the UV process is repeated.
Synthesis of Novel Allcyclic Polylmides and Application for
Liquid Crystal Alignment Layers
Alicyclic polyimides have recently attracted considerable attention because of many viewpoints, such as optical materials, low materials and so on. So far, we have developed novel type of alicyclic tetracarboxylic dianhydride (NDA), and attempted it to apply polyimide monomer. Ahcyclic polyimides were prepared by the two-step polymerization method, involving polyaddition forming poly(amic acid) and cyclodehydration. Polyimides with high molecular weights were obtained and was easily spin-coated into thin-film. Using spin-coated film, we prepared LCD cells, and we characterized the electrical properties. As a result, we have found that alicyclic polyimides containing NDA structure exhibit excellent high voltage holding ratio as liquid crystal alignment layers in LCID cells.
Siloxane- Poly Pyromellitimide Blends: synthesis and characterization
The incorporation of siloxane moiety in polyimide backbone has been attempted to derive mutual benefit of both polyimide and siloxane polymers. Unique characteristics in respect to permselectivity, resistance towards active oxygen and hydrolytic stability could be accomplished either by introducing suitable siloxane segments into the polyimide backbones and preparing their blends. As the part of the the studies being conducted at the Macromolecular Research Centre, Jabalpur, India, a new class of polyimide blends.alloys are synthesized using micromodification thechnques and appropriate characterization. Anovel blend of polyimide-siloxane are synthesized adopting the same concept and they are prepared first by reactng in common solvent, the polypyromellitamic acid with telomere of silanol terminated polydimethylsiloxane and folloed by thermal imidization. In order to establish the reaction mechanism, very high silanol telomer content was ~0.5% (i.e. Critical Crosslinker Concentration). The incorporation of covalently bonded siloxane moiety in polyimide was confirmed by FTIR and other physicochemical characterization. The degree of imidization, extent of the solvent embaded, the water sorption and the thermal properties of polyimide siloxane blends were determined. The structure-property correlation established from the preliminary data generated so far ae presented and further comprehensive characterization and evaluation of polyimide-siloxane blends having both high as well as microconcentration of silanol are under way.
Physico-chemical Characterisation of Polypyromellitimide/polybisitaconimide Blends
A high temperature resistant polyinaide resin matrix PBIT (Polybisitaconimide - an addition type polyimide) has bean blended by dispersing relatively high molecular weight polyimide polymer PPMD On. polypyromillitimide - a serniflexible condensation product) in the concentration range from 0. 5 to 3. 0% w/w). The improved[ mechanical properties were observed in carbon and kevlar fibre composites using this blended matrix and nevertheless, there was deterioration in mechanical properties of glass fibre composite. The values of TGA parameters of blended matrix has shown enhanced thermal properties in comparison to neat matrix. In this communication the two phase blend has been chosen due to its high glass transition temperature of over 300 C and favorable solubility of its precursor in common solvent. The PPMD component vitrifies much earlier than the main matrix. This results in the uniform dispersion of polyamic acid in PBIT prepolymer during the prepreg preparation stage and the product resulting after curing may be an isotropic blend wherein flexible polyimide macromolecules are dispersed at molecular level in a crosslinked polyimide matrix. The kinetics and physico-chemical characterisation. of the matrix are established by FTIR Spectroscopic and SEM analysis. The mechanism of interfacial interaction is predicted from the spectroscopic and microscopic data and the synergism in certain properties exhibited by these blends are explained.
Effects of Thermal Curing of Solvent Outdiffused PAAa Solution/gel on The Physico-chemical Properties of The Resultant Polyimide Film
Polyimides - the polymer containing heterocylic imide structure in the main macromolecular chain have emerged as potential high temperature resistant materials finding myriads of applications for frontier technologies like aerospace, microelectronics and advanced composites. The most notable use of polyimides is in microelectronic industry, primarily in applications such as films or coatings. The cure conditions used to convert polyamic acid precursor solution into films or coatings perform important function in the development of the morphology and the properties of resultant the polyimide films. The cure conditions for concurrent or stepwise removal of solvent and imidization were considered important as they influence the ultimate macroscopic properties. A new approach has been visualized to prepare polyimide films wherein the major quantity of solvent could be removed in first: step by outdiffusion into coagulating nonsolvent and finally solvent depleted polyamic acid precursor solution or gel is imidized thermally. Two process parameters during the outdiffusion stages viz; (i) time of coagulation and (ii) use of different coagulating agents have been varied and the resultant was subjected to fixed thermal curing conditions. The degree of imidization achieved, profile of solid-solvent content and the TGA derived paramters for the polyimide film prepared by various cure conditions are determined and the results are presented to establish the relationship between the curing parameters and the physico- chemical properties.
Residual Stress Evaluation of Aromatic Polyimide by X-ray Diffraction
Aromatic polyimides (PI) have excellent thermal stability, good mechanical properties and low electric constant, so they are widely used as microelectronics devices. When PI films are used as flexible printed circuitry boards and interlayer dielectrics, a thermal expansion mismatch between the film and the metal wiring causes residual stress at the interface through cooling down from the curing temperature to room temperature. Processing of PI from precursor polyamic acid (PAA) solution involves simultaneous imidization, evaporation of solvent and crystallization, so imidization process influences the final properties of PI. The residual stress at the interface between the most popular PI(PMDA-ODA) and the aluminum substrate was measured by X-ray diffraction method and the relationship between the microstructure and the mechanical properties was investigated for PI with different imidization processes. X-ray diffraction method was found to be powerful method to detect the residual stress non-destructively.
Dual Phase, Low Frequency Plasma Etching of Polyimide Films.
Etching large area (>12"X12") polyimide (Kapton) films using traditional 13.56 MHz plasma equipment is not a simple process. Being a good insulator, this material tends to build up a surface charge during plasma processing which can have a great effect on etch uniformity and overall results. Our experimental results have shown that there are synergistic effects between plasma frequency, electrode design and adsorbed water vapor on Kapton that all influence the plasma process. After a brief introduction to typical plasma etch problems encountered with typical plasma systems, some work will be presented using MetroLine's new dual phase 40 KHz etch system which is showing great promise for use in multi-layer flex circuit manufacturing.
Electrodeposition of Polypyrrole under the Magnetic Field
Intensive interest has been focused on the applications of polypyrrole (PPy) on microdevice components, due mainly to its excellent conductivity and high physical and chemical stability properties would not change even after boiling several days. However, the insolubility or intractability of polymer before melting prevents the use of conventional polymer-processing techniques in shaping the material into desired structures. In this paper, we investigated the influence of external magnetic field and the electrolytic cell structure on the growth patterns of PPy, in order to control the process of polymerization.
In the electrolytic cell with needle working electrode and circle or plate counter electrode, PPy was synthesized; the electrolytic solution consists of 0.1M monomer pyrrole, 0.1M sodium dodecyl benzene sulfonate (DBS) as electrolyte and acetonitrile as solvent.
When the polymerization was performed in the needle-circle electrode system, without applying magnetic field, the radical diffusion-limited-aggregation (DLA)-like pattern at 18V were got, reported in our previous paper. Once the magnetic field perpendicular to the current was applied, macroscopic convection of solution around the working electrode was observed clearly. When the magnetic filed is 0.1T, with direction from the top pointing to the bottom of the cell, the morphology at 18V showed anticlockwize spiral trend at tails of the main branches. The Lorentz force, which the magnetic field acts on the motional ions, induced lateral drifts in the motion of ions and brought about the anticlockwize convection. As a result, the polymer particles electrodeposited with a diverted direction and the spiral pattern presented. While the direction of magnetic is reversed, the convection is changed as well and the clockwize-winding pattern of PPy was got. When the magnetic field is 0.4T, the polymer electrodeposits were asymmetric winding branches. The winding trend of long branches was more obvious, with few short side branches on the long ones. The convection reduces the gradient of concentration and the diffusion layer becomes thinner. With thinner diffusion layer, the screening effect is reduced, so the distance between the branches is shortened and the
morphologies of PPy are denser.
In the asymmetric system: a square electric cell with the copperplate electrode set at the opposite sides, the morphology change of PPy was further studied. At 0T, the branches of PPy extended to the place where the copper plate set, reflecting the distribution of asymmetric electrical field. Under the magnetic field, the morphologies not similar to the above case, however, grow extending to almost every direction from the center and become denser. It may because the convection brings about the same diffusion possibility at every direction, which makes the asymmetric diffusion of ions under the asymmetric electrical field disappear. So the asymmetric morphology changed into symmetric one because of the effect of magnetic field. On the other hand, the morphology of PPy in the asymmetric electrical field under magnetic field becomes denser. The convection increases the velocity of diffusion, so the diffusion layer is thinner. With thinner diffusion layer, the screening effect is reduced, so the distance between branches is decreased and the morphology is denser.
In summary, the electrodeposits of PPy is dependent on the intensity and direction of Lorentz force, which the magnetic field acts on the motion of ions. In asymmetric system, the effects of magnetic field compensate the asymmetric electrical field distribution, resulting in the symmetric PPy patterns.
References
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Neville V. Richardson; School of Chemistry, University of St. Andrews, St. Andrews, Fife, KY16 9ST, Scotland
Controlled Coupling of Polyimide Precursors on Copper and Silicon Surfaces
The reaction of polyimide precursors with metal and semiconductor surfaces can be followed by surface sensitive techniques such as FTIR, EELS and NEXAFS. These can identify the chemical nature of the adsorbed species and its orientation. In the case of copper surfaces, pre-adsorption of oxygen has a marked influence on the chemical identity of the adspecies following exposure to anhydrides. The orientation of the molecular backbone is also affected and this has a strong influence on the subsequent coupling reactions. In the case of copper, the first molecular layer is preferred to be the anhydride species whereas on silicon surfaces, initiation with an amine is preferable. Amine adsorption on silicon occurs by N-H bond cleavage and formation of a strong covalent Si-N bond. Multilayers of alternating dianhydride and diamine can be grown on either surface with growth being monitored by vibrational spectroscopies.
1-Depto. de Química- Universidade Estadual de Marimgá- Maringá, PR-Brazil
2-Department of Chemistry- Virginia Tech-Blacksburg-VA , USA
Polyimides Doped With Copper Sulfide: Surface Conductive Films.
The surface of polymers can be previously modified to obtain a better interaction between organic polymers and inorganic materials. The objective of this work was the obtention and characterization of electrically conductable polymers/CuS composites, with emphasis on commercial Kaptonpolyimide In the previous treatment of the polyimide films with base, the presence of polyamic acid from the imid ring hydrolysis, was observed by FTIR-ATR spectroscopy. Studies of the influence of variables on the incorporation of copper sulfide in the commercial Kapton polyimide showed that without the treatment with base, there was practically no adherence of the copper sulfide to the polymeric matrix. Electric resistance as low as 1,0 ohm was measured in Kapton/CuS composites prepared in pH 1,4 at 80oC for 3,67 h. These conditions of preparation were optimazed by Response Surface Methodology. Electric resistance with an equal magnitude order was measured in composites of copper sulfide incorporated in polyimides films, synthesized in laboratory.
The composition of the surface was analyzed by photoelectron spectroscopy (XPS). Comparing the experimental data of carbon, oxygen and nitrogen contents to the theoretical ones for the original and for the treated polyimide, it is possible to say can be said that inside the an analyzed sampled extension, the hydrolysis of the material was practically complete. The presence of S (2p) and Cu(2p) peaks for the polymers/CuS composites demonstrate the incorporation of copper sulfide in the polymer surface. The scanning electron micrographies and the images of atomic force microscopy, which show an even CuS distribution matches very well with the low electric resistance found in the composites. By thermogravimetry and differential scanning calorimetry analysis, it was observed that the thermal stability, as well as Tg, of the polyimide was maintained In this way the composite presents the structural properties of the polyimide associated to the low electric resistance of the CuS.
Structural Materials Centre, Defence Evaluation and Research Agency
Farnborough, Hampshire, UK
High Glass Transition Temperature Epoxies
Epoxy systems based upon tetraglycidyldiaminodiphenylmethane resins (TGDDM) cured with diaminodiphenylsulphone (DDS) have been shown to exhibit glass transition temperatures (Tg) of approximately 260. Although this Tg value stems from a relatively high degree of crosslinking, which emanates from the multifunctional nature of the curing system, recent work has shown that intramolecular cyclisation reactions associated with the glycidyl groups on TGDDM have detrimental effects on Tg. In an attempt to overcome these effects, novel multifunctional epoxy systems have been developed which either eliminate the possibility of damaging intramolecular cyclisation reactions, or reduce the impact of such events.
Within this general theme, two novel chemistries have been considered. First, resins based upon quinoxaline have been developed in which terminal epoxide groups are sufficiently distant so as to prevent cyclisation. Tgs in excess of 300C have been observed. Second, resins derived from diaminodiphenylether have been prepared having epoxy functionalities up to 8, thus offering scope for substantial Tg enhancement.
The mechanical/fracture/thermal and water uptake characteristics of the novel multifunctional systems developed have been studied. Although substantial enhancements (relative to TGDDM) in Tg have been observed, these have, in some cases, been accompanied by reduced hydrophobic character. However, in most cases enhanced Tgs have occurred without any detrimental effects on mechanical properties.
This paper will consider the chemistry of the multifunctional systems developed and their properties, with particular emphasis on Tg, water uptake and mechanical behaviour.
(1) CERDATO/SPS, 27470 Serquigny, France
(2) CNRS/LMOPS, BP 24 69390 Vernaison, France.
Shape-memory Polymers : Copoly(aliphatic-aromatic)oxadiazoles.
The shape-memory effect (S.M.E.) is the ability of a material to be deformed into a temporary shape and to have its original shape restored by increasing the temperature.
A shape-memory polymer (S.M.P.) exhibits a rubbery domain above a glass or crystalline transition, and the elastic modulus of the rubbery domain is governed either by physical or chemical crosslinking.
The glassy modulus is between 100 and 1000 times higher than the rubbery modulus, so when the deformation has been frozen in the glassy state, the stored elastic stress cannot drive a reverse deformation. By heating a deformed thermoplastic polymer to the rubbery state, the residual inelastic deformation cannot be restored. In contrast a S.M.P. can recover almost all the residual deformation (1).
Different approaches have been investigated : Ethylene-vinylacetate copolymer containing 28 % of vinyl acetate was crosslinked by dicumylperoxide. The crystalline melting point of the small poly ethylene crystallites at 40 -50 ° C allows a reversible deformation in the rubbery state (2).
A network obtained by copolymerization of stearyl and methyl acrylates with methylene bis acrylamide shows a transition between glassy and rubbery states, due to a side organization of the stearyl groups (3). The S.M.E. of linear block copolymers have also been studied :
In the case of the polyurethanes the hard segments needed for a physical crosslinking are prepared with methylene di isocyanate and low molecular weight diols, the shape memory behavior is related to the crystalline transition of the polycaprolactone soft segment (4). Other segmented polyurethanes were investigated by a Mitsibishi team (5). Block copolyterephtalates containing polyethylenoxide terephtalate as soft segments and ethylene terephtalates as physical crosslinking agents also exhibit S.M.E. (6).
The first synthesis of the polyoxadiazoles was published by Marvel et al (7) using the reaction of bis tetrazoles with diacidchlorides. Two main methods have been studied, firstly, the intermediate formation of a polyhydrazide followed by a thermal cyclyzation (8-9), secondly the polycondensation in dehydrating medium such as oleum (10), polyphosphoricacid (11) or phosphoric anhydride and methanesulfonic acid (12). Both methods have their drawbacks and in this paper we present a new one step synthesis allowing the preparation of segmented aliphatic and aromatic oxadiazoles.
According to this method, the mixture of aliphatic and aromatic diacids reacts with the hydrazine sulfate. The formation of the block structures is due to the reactivity and solubility differences between both diacids. The copolymers structures are controlled by NMR and Xrays determinations .
A block copolymer containing 75 % of dodecanedioic acid and 25 % of isophtalic acid shows a crystalline transition at 80°C, a glassy transition at 220°C, and a rubbery state between these two temperatures, allowing a shape memory behavior.
1 Wei Z.G., Sandstrom R., Miyazaki S., J. Mater. Sci., 1998, 33, (15), 3743.
2 Li F., Zhu W., Zhang X., Zhaos C., Xu M., J. Appl. Polym. Sci., 1999, 71 (7), 1063.
3 Kagami Y., Gong J.P., Osada Y., Macromol. Rapid Commun., 1996, 17, 539.
4 Li F., Zhang X., Hou J., Xu M., Ma D., Kim B.K., J. Appl. Polym. Sci., 1997, 64, 1511.
5a Hayashi S., Kondo S., Kawamura K., Proc SPI annu. Tech. Mark. Conf., 1992, 34th Polyurethan).
5b Liang C., Rogers A., Malafeew E., J. Intell. Mater. Syst. Struct., 1997, 8(4), 380
6 Luo X., Zhang X., Wang M., Ma D., Xu M., Li F., J. Appl. Sci., 1997, 64, 2433.
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12 Ueda M., Sugita H., J. Polym. Sci., Polym. Chem. Ed, 1988, 26,
UV Laser Micromachining of SU-8 Polyimide to Produce High Aspect Ratio Structures for MEMS
(Abstract not yet available)
Preparation of Noble Metal Nanoclusters in a Polyimide Matrix by Vapor Phase Deposition
Nanometer-sized metal particles dispersed in a dielectric polymer matrix have recently received considerable attention because of their interesting optical and electrical properties and their potential use in catalytic applications [].Usually this kind of composite materials is prepared from solution or by plasma deposition. Here we report on the preparation of metal clusters in a PMDA-ODA polyimide matrix by thermal coevaporation based on a vapor deposition process for polyimides []. The metal-polymer composites were characterized using transmission electron microscopy. After codeposition of PMDA and ODA with copper only very small clusters are formed. During thermal treatment the clusters grow in size and finally at 523 K spherical clusters up to a diameter of 25 nm are formed within the polyimide matrix. No further cluster growth is observed at temperatures above 523 K. Similar experiments with nickel resulted in much smaller clusters of finally only 4 nm diameter and a narrower distribution. The cluster formation process and the influence of metal-polymer interaction and diffusion will be discussed.
Initial stages of polyimide metallization
Metallization of polyimides is important e.g. for microelectronic applications. Here we report on the initial stages of metal/polyimide interface formation in particular on the condensation of metal atoms onto a polyimide surface, diffusion of metal atoms on a polymer surface and into the polymer bulk, nucleation and growth of metal clusters on the polymer surface, and chemical interaction of metal atoms with the polyimide. The focus will be on copper and silver evaporation onto polyimide studied by a combination of x-ray photoelectron spectroscopy, transmission electron microscopy and a very sensitive radiotracer technique. The combination of these techniques allows to obtain a very detailed picture how the initial stages of metal/polymer interface formation are influenced by the experimental conditions. Particular attention will be paid to metal cluster density and metal diffusion into the bulk and its variation with substrate temperature, deposition rate and subsequent annealing treatments. Results for other metals like Au, Ni and Cr and other high temperature polymers will also be discussed briefly.
Nucleation Growth and Aggregation of Gold on Polyimide Surfaces
The growth of ultra-thin gold films on polyimide (PI) surfaces and the stability of the films upon thermal annealing have been studied using a combination of various techniques. With scaning electron microscopy (Sem), we observe that, at room temperature, the Au film initially grows by nucleation of compact Au islands. With increasing metal coverage, the clusters partially agglomerate to produce a work like structure. Finally, percolation, hole filling and continuous film growth are observed. To evaluste the thermal stability og the Au/PI system, annealing at various temperatures was performed on films that displayed the worm-like structure. SEM results indicate strong temperature dependent changes in film morphology. Finally, from our SEM data we determine contact angles, allowing us to estimate interfacial and adhesion energies.
Behavior of Glass or Carbon Fiber Fabric Reinforced Polyetherimide after Natural and Accelerated Aging
Static and dynamic tests have been performed on two different composites. One of them formed by a thermoplastic matrix and carbon fiber fabric and the other with glass fiber fabric. The evolution of the mechanical properties, static (tensile and interlaminar shear strengths) and dynamic (fatigue life to three different levels of stress) of this material due to natural and accelerated aging have been followed. The natural aging consisted of exposure to the inclemency of the weather during two years and the accelerated aging was carried out in a saline atmosphere at a temperature of 37ºC and a relative humidity of 98% during 200 days. A negligible influence of these types of exposure on the different properties have been obtained from the tests carried out in both composite materials.
1Institute of Materials Research and Engineering (IMRE) Blk S7, Level 3, 10 Kent Ridge Crescent, Singapore 119260
2Department of Chemical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
Measurements and Theoretical Estimations of Dielectric Properties of Polyimides
Polyimides are versatile engineering resins. Some of these Polyimides show low relative dielectric constant (permitivity), low dielectric losses over a wide frequency range. These Polyimides are particularly attractive as interlevel dielectrics in integrated circuit fabrication. A low dielectric constant is necessary to get interlevel insulation to prevent cross talk in miniaturized muti-level chip for high-speed signal propagation. Reducing the dielectric constant of insulation materials enhances the ability of electronic device with higher speed of signal propagation. Desirable dielectric constant values of Polyimides for such applications should be less than 3.0. The dielectric constants of commercially available Polyimides are in the range of 3.2 to 3.5.
It is surprising to note that only handful of technical papers has been published on the estimation/prediction of dielectric properties for polyimides. In fact, through the estimation of dielectric properties, we can:
The "Molar Polarization" values of various conjugated groups which are present in chemical structure of Polyimides were derived by additive group contribution method suggested a bookProperties of Polymers by D. W. Van Krevelen, Elsevier Science Publishers B. V., 1990
For the first time, we have reported here in this paper, the "Molar Polarization" values determined for the very important Phthalimide and especially the Pyromellitimide, etc. groups typically present in non fluoro-polyimides and Hexafluoroisopropyledene, etc. in Fluoro-Polyimides structures.
Also, we have very satisfactorily incorporated these values in the mathematical equations defined by Lorents-Loren'z theory and Vogel's theory for various polyimides and copolyimides synthesized in our lab and used in our study, such as BPDA+mPDA, PMDA+ODA, 6FDA+Durene Diamine, etc. We have estimated, tested and verified the dielectric constant values calculated at 1 kHz against actual laboratory dielectric measurement experimental data. The estimated dielectric constant values are in good agreement with the experimental and literature values. Thus it is established that this method would help to calculate the molar polarization values of various monomer groups typically present in the polyimide structure. In turn it would simplify estimation/calculation of dielectric constant of huge number of new Polyimide compositions before they are ever synthsized. We have calculated and provided a list of molar polarization values of several dimides and partial diamine moieties typically present in the Polyimides structures.
Thermal and Uv-laser Pyrolysis of Kapton: a Comparative Study.
Thermal and UV-laser pyrolysis of a thin film polymer (Kapton) was studied to determine the gaseous products evolved and to elucidate a potential mechanism for decomposition. Thermal pyrolysis covered a temperature range from 600°C to 1300°C in 50 degree increments. Non-ablative laser pyrolysis was conducted using an Argon ion laser at 363.6 nm. The results from the UV-laser pyrolysis show that the principal gaseous products evolved are CO, CO2, C2H2, CH4 and HCN. The only gaseous products observed in the thermal pyrolysis study are CO and CO2 with the principle component of thermal pyrolysis being carbon dioxide. The percentage of carbon monoxide evolved was much less than that of carbon dioxide evolved both in the thermal and UV pyrolysis. However, in the thermal pyrolysis the concentration of both products increased with temperature. These results help provide essential information for the analysis of the chemical properties of the commercial polyimide Kapton and a better understanding of the polymer carbonization process.
Modeling Adhesion at the Polyimide-Silica Interface
We describe a total strategy for modeling adhesion at the polyimide-silica interface. Our candidate polyimides are pyromellitic-dianhydride oxydianiline (PMDA-ODA) and pyromellitic-dianhydride hexamethyldiamine (PMDA-HMDA). In particular, the strategy of the initial stage of this investigation, that of calculating the strength of bonds across the polyimide-silica interface, is presented in detail. Results of our quantum chemical calculations in the estimation of polyimide flexibility are also presented. We also discuss the findings for our theoretical characterization of the hydrolyzed, amorphous silica surface. Finally, we outline future calculations of the polyimide-substrate interaction energy.
1) Institute of Space and Astronautical Science, 3-3-1 Yoshinodai, Sagamihara-shi, Kanagawa Japan 229.
2) Departmet of fApplied Chemistry, Faculty of Science and Engineering, Nihon University. Ochanomizu, Chiyoda-ku, Tokyo 101
3) Department of Chemistry, Faculty of Science, Toho University. 2-2-1 Miyama, Funabashi, Chiba, Japan 274.
4) Polymer Research Laboratory, R&D, Ube Industries, LTd. Goi Minamikaigan,Ichiharai-shi, Chiba, Japan 290
Novel Phenylethynyl-Terminated Asymmetric BPDA Polyimides Having Excellent Processability And Thermo-Oxydative Stability
Novel phenylethynyl-terminated, addition type polyimide oligomers consisting of 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA) and 3,4'- oxydianiline (3,4'-ODA) and/or 4,4'-oxydianiline(4,4'-ODA) with phenylethynyl phthalic anhydride (PEPA) were prepared. The oligomer derived from a-BPDA and 3,4'-ODA; 4,4 $B%f (B-ODA (1:1) comonomer with PEPA having polymer units n=1.5 or n=10 showed good solubility in aplotic solvents such as DMAc and NMP and were successfully converted to crosslinking structures after curing at 370 deg. C for one hour. It was observed that the melt flow property dramatically decreased above the Tg for the n=1.5 oligomer, resulting in a viscosity as low as 200 poise at 300 deg. C during the cure process. The glass transition temperaturesof these cured oligomers were 341 deg. C and 308 deg. C respectively. In addition to the excellent melt property, the cured oligomers not only n=10, but also n=1.5 exhibited incredible toughness, and thermo-oxydative stability. Furthermore, for the cured oligomer consisting of a-BPDA/4.4'-ODA and PEPA(n=4.5) and its T-300 carbon fiber composites, the molding resins were well consolidated and exhibited over 13 % flexural elongation in addition to a high Tg of 343 deg. C, and giving a significant improvement in processability and high composite properties. Such excellent properties in these a-BPDA based addition type polyimides demonstrate a high potential for future aerospace applications.
Synthesis and Characterization of New Polyimides Containing Fluorine and Phosphine Oxide Moieties
A monomer having fluorine and phosphine oxide moieties (3,5-bis(trifluoromethyl)phenyl diphenyl phosphine oxide (6FPPO)) was prepared via Grignard reaction which was subjected to nitration and reduction to afford a diamine monomer of bis(3-aminophenyl) 3,5-bis(trifluoromethyl)phenyl phosphine oxide (DA6FPPO. Bis(3-aminophenyl) phenyl phosphine oxide (DAPPO) was also prepared from triphenyl phosphine oxide (TPPO) for comparison purpose. Those monomers were characterized by FT-IR, NMR (1H, 31P, 19F) and utilized to synthesize polyimides with PMDA, BTDA, ODPA and 6FDA. Polyimides were prepared via two step process; preparation of poly(amic acid) followed by solution imidization and the molecular weight was controlled by addition of phthalic anhydride. Polyimides were characterized by DSC, TGA, FT-IR and viscometer, and also subjected to property measurements such as adhesive properties and electrical properties.