Several segmented, rigid-rod polyimides have been prepared that are soluble in organic solvents in their fully imidized form. The polymers were prepared from commercial dianhydrides and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB). Their intrinsic viscosities ranged from 1.0 to 4.9 dL/g. Tough, colorless films could be cast from m-cresol solutions at 100°C. The polymers had glass transition temperatures (Tgs) above 275°C and displayed outstanding thermal and thermo-oxidative stability. Fibers were prepared from the 3,3′,4,4′-tetracarboxybiphenyl dianhydride (BPDA) based polymers that had moduli of 130 GPa and tensile strengths of 3.2 GPa. The thermal expansion coefficients and dielectric constants of thin films (20–25 μm) of the polymers were as low as −2.40×10−6 and 2.5, respectively.

C. C. Walker[1] first demonstrated that size exclusion chromatography (SEC) is an effective analytical technique for observing molecular weight distribution changes (MWD) of polyamic-acids with time. The specific polyamic-acid studied was that based on pyromellitic dianhydride and 4,4′- oxydianiline (PMDA/ODA), and the MWD narrowed on aging. Essentially, a decrease occurred in the weight average molecular weight (Mw), but no change took place in the number average molecular weight (Mn). Redistribution of molecular weight was postulated to be due to an equilibration reaction arising from the reversibility of amic-acids[2]. Additional data on Mw decreases with time of polyamicacids other than PMDA/ODA have been reported by Miwa and Numata[3] and Kreuz[4], and although trends are similar, rates of equilibrations of various polyamic-acids appeared to be partially due to backbone structure. The dianhydrides of 3,3′,4,4′-biphenyl dianhydride (BPDA) and 3,3′,4,4′- oxydiphthalic anhydride (ODPA) tended to give more stable polyamic-acid solutions.

The modification of the pendant acid groups along the poly(amic acid) backbone in the form of alkyl ester groups leads to greatly improved polyimide precursors. These poly(amic alkyl esters) are characterized by the absence of hydrolytic instability due to elimimation of the “monomer-polymer” equilibrium associated with poly(amic acids), a broad imidization temperature regime, improved solubility characteristics, and enhanced mechanical properties. In the absence of hydrolytic instability, it is now possible to use an aqueous work-up of the polyimide precursor. This presents an attractive synthetic pathway for the preparation of well-defined, amine-terminated oligomers. Such oligomers can then be utilized both in the preparation of low molecular weight, chain-extendable polyimide precursors as well as polyimide block copolymers. The higher imidization temperatures offered by the “amic ester” chemistry allows for more efficient chain extension prior to imidization. Alternatively, the lack of the “monomer-polymer” equilibrium and accompanying propensity for monomer randomization reactions presents a potential pathway for the preparation of polyimide blends.

Trifluoromethyl group-containing polyimides not only show extraordinary electrical properties, but they also exhibit excellent long-term thermo-oxidative stability. Among the most thermomechanically stable structural polyimides are those from 6F dianhydride (6FDA) and 6F diamines. The effects of substituting non-fluorine containing monomers such as BTDA, mPDA and 4,4′-DADPS for the hexafluoroisopropylidene monomers on the dielectric, thermo-oxidative, thermal and mechanical properties of the copolymers were studied.

Block copolymers based on the poly(amic ester) of poly(4,4′-oxydiphenylene-pyromellitide) and perfluoroalkylene aryl ethers were synthesized from preformed amine terminated perfluoroalkylene aryl ether oligomers. Fluoropolymer structure, wt% incorporation, and molecular weight were varied. Reduction in the dielectric constant to 2.8–2.9 and reduced moisture sensitivity were observed for block copolymers with 55 wt.% poly(perfluoroalkylene aryl ether) content without significant compromise of mechanical or thermal properties.

New fluorinated copolyimides are synthesized with 2,2′-bis(trifluoromethyl)-4,4′- diaminobiphenyl (TFDB) and a mixture of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and pyromellitic dianhydride (PMDA). The thermal expansion coefficient decreases with decreasing 6FDA content, because the hexafluoroisopropylidene group makes the main chain flexible. The refractive index decreases with increasing 6FDA content, because the fluorine content increases. The thermal expansion coefficient can be controlled between -0.5 × 10−5 and 8×10−5 /°C, and the refractive index can be controlled between 1.556 and 1.647 at 589.3 nm, by changing the 6FDA content. The polyimides and copolyimides from TFDB can be used in optical filters because of their high optical transparency and low thermal expansion coefficient. They are expected to be used in optical waveguides because of their high optical transparency and refractive index control.

A dry ultra high vacuum technique for the preparation of polyimide films is investigated as an alternative to standard wet processing techniques involving the use of solvents. This technique is based on the co-deposition of monomers (pyromellitic dianhydride and oxydianaline in this study) to form polyimide (poly (4,4′-oxydiphenylenepyromellitimide)). Various parameters to optimize film growth are investigated and the properties of the films are compared to films prepared by spin casting from solution. Films from 10Å to 15 μ were grown. Uniform films over 3 inch wafers were successfully grown. Many properties such as adhesion, dielectric constant and stress were similar to spun films. H-lowever, these films did exhibit more crystalinity but less orientation than the spun films. Finally, being a vapor phase process the rdms were conformal rather than planar.

A series of new poly(enaminonitriles) were synthesized by the condensation polymerization of three different bis(chlorodicyano-vinyl) aromatic monomers with various aromatic diamines. These polymers have moderate to high molecular weight with intrinsic viscosities ranging from 0.35 to 0.77 dl/g and form flexible films. These polymers exhibit good solubility in many organic solvents and excellent thermal stability, retaining their weight up to 400 °C in air. Poly(enaminonitriles) undergo ‘curing’ reactions at high temperature (˜300 °C) to provide insoluble, infusible material without emission of volatile by-products. Dielectric constants of these polymers ranged from 3.5 to 5.2 depending on the structure. Their thermal and dielectric properties are correlated to the structures.

Polyimide-silica hybrid films were successfully prepared by the sol-gel reaction starting from a mixture of tetraethoxysilane (TEOS), a solution ofpolyamic acid in N, N-dimethylacetamide and water of pH 7 and pH 3. The hybrid films were obtained by the hydrolysis-polycondensation of TEOS in the polyamic acid solution, followed by heating at 270°C. Fairly flexible films were obtained for silica contents up to 70 wt%. The films containing less than 8 wt% of silica were yellow and transparent, whereas the films with higher silica contents were yellow and opaque. The density of the silica in the hybrid films was estimated to be 1.65 and 1.69 g/cm3 (pH 7 and pH 3). The29Si nuclear magnetic resonance spectrum indicated that the silica in the films consisted of non-hydroxy, monohydroxy, and dihydroxy siloxane structures. Silica particles with submicron diameter were observed in the hybrid films containing less than 8 wt% silica, whereas larger particle size around 5 μ m in the case of higher silica content. The decomposition temperature of the hybrid films increased with increasing silica content. The glass transition temperature of the hybrid films showed the minimum at 8 wt% of silica content. Tensile properties, such as elongation at break, tensile strength, and tensile modulus also exhibited the same tendency. The linear thermal expansion coefficient of the silica in the hybrid films was estimated to be 1.3 × 10−5 and 0.3 × 10−5 (pH 7 and pH 3), which suggested that the silica had a porous structure.

Imide-aryl ether ketone block copolymers were prepared and their morphology and thermal and mechanical properties investigated. The key feature of this copolymerization is the preparation of soluble aryl ether ketimine oliogmers which may be subsequently hydrolized to the aryl ether ether ketone form. A bis(amino) aryl ether ketimine oligomer was prepared via a nucleophilic aromatic substitution reaction with a molecular weight of 6,000 g/mol. The oligomer was co-reacted with 4,4′-oxydianiline (OI)A) and pyromellitic dianhydride (PMDA) diethyl ester diacyl chloride in N-methyl-2-pyrrolidone (NMP) in the presence of N-methylmorpholine. The copolymer compositions, determined by II-NMR, of the resulting amic ester based copolymers ranged from 8 to 20 wt% aryl ether ketimine content. Prior to imide formation, the ketimine moiety of the aryl ether ketimine block was hydrolyzed (p-toluene sulfonic acid) to the ketone form producing the aryl ether ether ketone block. Solutions of the copolymers were cast and cured to effect imidization, producing clear films. The copolymers displayed good thermal stability with decomposition temperatures in excess of 450°C. Multiphase morphologies were observed irrespective of the co-block type or composition.

Three kinds of thermoplastic/thermosetting polyimide blends have been prepared using three kinds of commercially available soluble polyimides(AL1051, PI2080, Ultem) and N, N′ – (methylenedi-p-phenylene) bismaleimide(BMI). The DSC thermograms of the polyimide blends showed exotherms at higher temperatures compared to BMI alone. The cure characteristics of the blends changed significantly according to the thermoplastic polyimide component. The fracture surfaces of PI2080 and Ultem blends, examined under a scanning electron microscope, showed distinct nodular morphological features. However, in the case of AL1051, which was derived from a aliphatic acid, this kind of phase separation was not observed. The mechanical properties of the blends were studied by using a thermomechanical analyzer. The blends yielded films with good mechanical properties even at high temperatures. The BMI component did not have any significant effect on the glass transition temperatures. However it showed improved mechanical properties at high temperatures. The blends were brittle compared with the thermoplastic polyimides. The tensile and electrical properties of the blends and their coefficients of thermal expansion were also studied.

High purity high molecular weight poly (phenylsilsesquioxane) (PPSQ) has been synthesized and specimen films prepared by a solvent casting method. The decomposition temperature of the material is 550°C in air. A PPSQ specimen cured at 350°C for 60 min has a weight loss of 1% when held at 460°C for 60 min. A specimen initially dried at 200°C for 30 min then held at 460°C loses twice as much. The main constituent of the volatile material from PPSQ pyrolyzed at 500 °C for 60 min is benzene, which is 5.7% of the specimen weight. The tensile strength for the cured specimen is 8.0 × 109 dyne/cm2 at 25 °C, and 5.5 × 109 dyne/cm2 at 250°C. The strength of the dried specimen is 4.0 × 109 dyne/cm2 at 250°C and about one half that at 25°C. The thermal expansion coefficient for the cured specimen is 11−14 × 10−5 /°C over a temperature range from 5°C to 350°C. Residual stress is 2.8 × 108 dyne/cm2 at 25°C and one order lower at 350°C.

The thermal polymerization reaction of divinyl siloxane bis-benzocyclobutene (DVS bis-BCB) was monitored in-situ with FT-IR spectroscopy in order to follow specific chemical changes and determine the reaction order and rate constants at temperatures from 150° to 210°C. FT-IR spectra were obtained at regular intervals throughout the reaction with a Nicolet 170SX spectrophotometer.

Monomeric DVS bis-BCB contains mixed stereo and positional isomers of 1,3- bis(2-bicyclo[4.2.0]octa-1, 3, 5-trien-3-ylethenyl)-1, 1, 3, 3-tetramethyl disiloxane (CAS 117732-87-3). It polymerizes via Diels-Alder cycloaddition reactions between vinyl groups and an intermediate o-quinodimethane formed by first-order, thermally initiated ring openings of the benzocyclobutene rings. Gaseous byproducts are not produced; therefore, the cure is easier to manage than are cures for polyimides which evolve water in polycondensation reactions. The DVS bis-BCB has four reactive elements per monomer unit and, thus, polymerizes into a very highly cross linked and solvent resistant network.

With the FT-IR methodology, the reaction was easily monitored through the points of gel formation and vitrification. With the exception of DSC (i.e., calorimetry) which does not sense specific chemistry, other methods were not successful in following the reaction after a gel was formed. We have found that the polymerization was first-order until vitrification occurs; the gelation alone had no apparent effect on the reaction rate.

DVS bis-BCB is under development at Dow as high performance dielectric material for multilayer interconnect coating applications for the microelectronics industry. Methodology reported here is employed in developing effective cure management strategies.

The use of polyimides in integrated circuits to planarize complex topography and the need to decrease the dimensions of electronic devices have motivated us to gain a better understanding of the details of the polymer microenvironment. UV/Vis absorption experiments suggest that intramolecular charge transfer (ICT) exists and therefore might utilized as intrinsic, nonperturbing probes. The transfer of charge is believed to occur upon exposure of ultraviolet light as a result of donation from the phenyl ring (from the diamine fragment) to the adjacent imide ring. Furthermore, the transfer of charge should be a function of the torsional angle between the planes of the donor and acceptor segments.

In this study, we first investigate the nature of the ICT by conducting UV/Vis absorption measurements on a series of model compounds. A comparative analysis of 10−5 M solutions of the models in dioxane provides evidence that intramolecular charge transfer occurs when the compounds are exposed to 264 nm (ultraviolet) light. Similarly, a comparison of an analogous series of polyimides demonstrates that the same phenomenon occurs in the more complex polymeric systems when spin-cast films are exposed to 326 nm (ultraviolet) light

The emission mechanisms of solid PI(BPDA/PDA) derived from biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) were examined with the absorption and fluorescence. spectra of model compounds (denoted by M). M(BPDA/CHA) (CHA: cyclohexyl amine) fluoresces at ca. 430 nm in hexafluoro-2-propanol(HFP) solution, while M(BPDA/AN) (AN: aniline) does not. PI(BPDA/PDA) film does not show the monomer fluorescence of biphenyldiimide unit, but shows only intermolecular CT fluorescence peaking at 530–540 nm. This suggests that for PI(BPDA/PDA) film and PI(BPDA/AN) in solution the local excited state of biphenyldiimide units is deactivated owing to intramolecular charge-transfer(CT).

The intermolecular CT fluorescence reflecting sensitively molecular packing of PI chains was used to monitor isothermal imidization process of poly(amic acid)(PAA) of BPDA/PDA. The fluorescence of PAA(BPDA/PDA) peaking at 490 nm decreases rapidly and disappears at 30–40% conversion, then the fluorescence of PI(BPDA/PDA) peaking at 540 nm increases gradually during isothermal imidization. The fluorescence intensity at 540 nm increases rapidly as imidization proceeds when imidized at higher temperature. A kinetic study on isothermal imidization shows that the vitrification is strongly related to the reorientation of polymer chains and the final PI structures.

Isothermal annealing studies reveal long term increases in charge transfer fluorescence in spin-cast BTDA-ODA/MPD films. Due to the amorphous nature of these materials, the increase in charge transfer complex (CTC) population is attributed to thermally activated hindered rotation leading to local segmental correlations. This ordering process is driven by the non-equilibrium structure of the initially imidized film. Increased in-plane orientation at higher spin speeds produces a stress activation effect, lowering the energy barrier for segmental rotation.

Organo-soluble rigid-rod and segmented rigid-rod polyimides and their copolyimides exhibit isotropic solutions in hot m-cresol, but form gels upon cooling. A lyotropic liquid crystal phase is observed below the gel/sol transition. Mechanical gel formation is caused by liquid-liquid phase separation, while the liquid crystal phase may be formed through a nucleation process after gelation. High performance fibers can be spun from the hot isotropic solutions using a dry-jet wet spinning method. After the fibers are drawn at high temperatures, they display tensile strength higher than 3.2 GPa and an initial modulus higher than 130 GPa. In particular, the fibers retain relatively high mechanical properties at elevated temperatures. Solution casted films exhibit very low thermal expansion coefficients and dielectric constants. Their structure, morphology and property relationships will also be discussed.

Moisture absorption and its effect on electrical properties were measured for several polyimides. A Quartz Crystal Microbalance (QCM) was used to investigate the moisture absorption in BPDA/PPD, PMDA/ODA, and BTDA//ODA/MPD polyimides. The steady-state moisture uptake in polyimides as a function of relative humidity (RH) was determined by exposing film samples to successively higher RH values ranging from 10 to 85% at 25°C. The isothermal moisture absorption as a function of percent RH was found to be nearly linear for all of the polyimides studied. The effect of moisture on the electrical properties of a BPDA/PPD polyimide was also investigated. The relative dielectric constant at 25 °C was found to be a linear function of the moisture absorbed.

The bismaleimide resin Matrimid 5292A (I) was cocured with an allylnadic-imide resin (EP 433) which contained a long aliphatic chain as backbone (II). Water uptake, swelling, and the dielectric properties (up to 300 MHz) were studied in cast plates. The dielectric constant varied from 5.4 in (I) to 3.2 in (II) at water saturation, compared to 3.1 in (I) to 2.7 in (II) in the dry state. The glass transition temperature stayed above 200 °C at less than 80 mol% of (II).

Solution and solid state Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) spectroscopy have been used to monitor the 31P signal of cyclic phosphazenes and associated linear polymers in solution and of these materials bound to alumina in stabilized dispersions. The differences between the simple solution experiments and the suspensions are being studied to determine the viability of NMR techniques to probe the chemical interactions between inorganic polymer dispersants and alumina particles. It has been observed in colloidal suspensions that the adsorption of phosphazenes onto an aluminum oxide surface causes a broadening of the 31P signal in solution NMR. This broadening is dependant on the amount of solid to polymer concentration, the amount of solids loading, the solvent polarity and the phosphazene substituent under investigation [1]. Conversely, the solid MAS experiments show a narrowing of the 31P signal upon adsorption of the phosphazene to alumina.