Polyimides commercially available

Different dianhydrides have been syndiesized or are commercially available, and some structures arc shown in Fig. 5.9.64-66 An improved method for preparation of cyclobutanetetracarboxylic dianhydride (CBDA) by photochemical dimerization of die maleic anhydride has been developed by Nissan.67 The polyimide obtained by condensation of CBDA widi oxydianiline gives a transparent and colorless material. The transmittance of 50-pm-thick film is 82% and the UV cutoff is 310 nm. 

Principally, one commercially available sulfonated diamine (4,4 -diamino-2,2 -biphenyl disulfonic acid) has been used to synthesize sulfonated polyimides. In addition to the commercially available diamine, several novel sulfonated diamines incorporating flexible or kinked structures have been prepared in Okamoto s lab. " The chemical structures and names of all five diamines are shown in Figure 23. 

Polyetherimides (PEI) are polyimides containing sufficient ether as well as other flexibi-lizing structural units to impart melt processability by conventional techniques, such as injection molding and extrusion. The commercially available PEI (trade name Ultem) is the polymer synthesized by nucleophilic aromatic substitution between 1,3-bis(4-nitrophthalimido) benzene and the disodium salt of bisphenol A (Eq. 2-209) [Clagett, 1986]. This is the same reaction as that used to synthesize polyethersulfones and polyetherketones (Eq. 2-206) except that nitrite ion is displaced instead of halide. Polymerization is carried out at 80-130°C in a polar solvent (NMP, DMAC). It is also possible to synthesize the same polymer by using the diamine-dianhydride reaction. Everything being equal (cost and availability of pure reactants), the nucleophilic substitution reaction is probably the preferred route due to the more moderate reaction conditions. 

Poly[2,2 -(m-phenylene-5,5 -benzimidazole)] (PBI) is a very high glass transition temperature (Tg 430°C), commercially available material. It possesses excellent mechanical properties, but is difficult to process into large parts and has high moisture regain and poor thermo-oxidative stability at temperatures above approximately 260 °C. Polyimides, especially the thermoplastic polyimides, offer attractive thermo-oxidative stability and processibility, but often lack the thermal and mechanical characteristics necessary to perform in applications such as the matrix for high use-temperature (over 300 °C) structural composites (for example, carbon fiber reinforced) for aerospace use. The attempt to mitigate... 

Further, since dianhydride and diamine structures of wide structural variety are commercially available, an extensive range of polyimide homo- and copolymers can be easily synthesized. This allows structural optimization for applications or fundamental studies. A representative, though far-from-complete, list of monomers can be found in Tables 13.1 and 13.2. 

POLYIMIDES. These are heat-resistant polymers which have an imide group (—CONHCO-) in the polymer chain, Polyimides, poly(amide-imides), and poly(esterimides) are commercially available,... 

Other membrane materials include mainly polyimide, polyacrylonitrile and polybenzimidazole. An overview of commercially available membranes is given in Table 3.2. These membranes are manufactured in procedures usually derived from practical experience by using high-throughput screening, it was shown that optimization is possible [26]. Many other membrane materials are described in the scientific literature and in patents an overview is given by Cuperus and Ebert [27]. 

The physical properties of systems having imide groups incorporated with epoxy resin was not seen until much later. Researchers in Korea performed microscopic analysis of commercially available polyetherimide (ULTEM1000) modified epoxy resins [40]. In their work, electron micrographs of the systems showed a two phase system even though their systems were limited to polyimide contents of less then 10 wt%. Compatibilizing polyesterimides with polyetherimides in order to fabricate in situ epoxy composites was addressed by Seo et al. [41]. 

Two membrane types that operate on different principles have been used in commercially available membrane separators microporous membranes and selectively permeable, nonporous polyimide or Nafion membranes. The micro-porous Teflon PTFE membrane can be used to remove water vapor or organic solvent vapor. Any gaseous component, including volatile analytes such as Hg, is partially or extensively removed. The sweep gas flow rate is typically similar to the sample carrier gas flow rate. 

The Influence of the Matrix Precursor. The first requirement for a suitable matrix precursor is high carbon yield, which must be achievable under simple pyrolysis conditions. Figure 14 (left-hand side) shows weight loss as a function of pyrolysis temperature for several matrix precursors practical precursors that are commercially available include coal-tar and petroleum pitches, phenolic resins, polyimides, and the para-polyphenyleneacetylene resin Hercules HA 43 (35,36) The structural formulas of some polymer binders are shown in Figure 15. 

The organic dielectrics known as polyimides have been studied extensively by a variety of bulk characterizational techniques as a perusal of the literature will illustrate. Little has been published on their surface properties. X-ray photoelectron spectroscopy (ESCA) has been extremely useful for polymer characterization (, 7, ), In a previous paper ( ), we have reported the ESCA spectra of structurally different polyimides derived from both commercially available polyamic acid resins (DuPont s PI5878, PI2525, PI2550), and from laboratory synthesized polyamic acid resins. 

The main source of the alpha particles is trace quantities of uranium and thorium in the silica filler. Because silica fillers that did not contain these radioactive elements were not available, other methods for preventing alpha particles from reaching the active DRAM cells were devised. These early methods consisted of cov-vering the active cells with either a silicone or polyimide chip coat or with Rapton tape. These methods added extra steps to the manufacturing process which were cumbersome and labor intensive and, if not done precisely, had a negative reliability impact. These processes were not widely used once "low alpha fillers" became commercially available in 1982/1983. Initially, these "low alpha fillers", which contain <1 ppb uranium, were only available from one or two natural sources. Now, however, there are additional natural and synthetic sources of silica, all of which contain <1 ppb of uranium and have an alpha particle emission rate of less than. 001 alpha particles/hr-cm. Figure 9 shows where the industry was in 1980 and where it stands today. An improvement by a factor of 30-50 has been achieved with "lower alpha" filler and compound manufacturing. 

For the method development of the SEC separation, the main attention should be focused on the suppression of analyte interactions with the surface of packing material. This usually requires a careful selection of the SEC column. In GPC, commercially available synthetic organic polymer columns are usually packed with styrene-divinylbenzene copolymer particles, which are only capable of weak dispersive interactions. Any possible analyte interactions with the surface could be suppressed by using a strong solvent, which will be preferentially adsorbed on the packing material surface. Selection of such a solvent is limited since the polymer solubility in that particular solvent needs to be considered. Tetrahydrofuran is the most common solvent used for most GPC separations, although for polyimids and other high-temperature polymers the use of special solvents such as n-methylpyrrolidone may be necessary. 

Many hundreds of different composite compositions have been tested for use in ball or roller bearings, mainly for space use. Some examples of results with polymer-based composites are shown in Table 12.11 and with metailic compacts in Table 12.12. Among the polymeric composites the best results have been reported with composites of PTFE or polyimide. Bearings are commercially available with composite retainers based on either polymer. 

Another application in which thermal FFF enjoys an advantage over SEC is the analysis of high-temper-ature polymers. The operating temperature is limited only by the degradation temperature of the spacer used to form the channel, which for polyimides can be as high as 600 K. In the analysis of high-molecular-weight polyethylene, for example, temperatures in excess of 400 K are required for the samples to be soluble. Under these conditions, column stability and separation efficiency limit the application of SEC. By contrast, such samples can be routinely analyzed with commercially available thermal FFF channels. 

In the stand-alone application (Figure la) the SOG film must have good dielectric characteristics and a thickness range of 1-2 microns. No such SOG materials are currently commercially available. Polyimides have adequate electrical characteristics and can be spin-applied into films up to several microns thick. However, they have not been widely adopted because of difficult processing required in their use and certain Inherent limitation in material characteristics. The smoothing layers schemes ( ), (c), and (d) of Figure 1 require a thickness of only 1000-3000A for the SOG film. The electrical properties of the SOG film in these structures are relatively less critical since the bulk of the dielectric function is... 

Fluorescence spectra of polyimide as a function of thermal history for two of the most common commercially available polyimide precursors, Du Pont PI-2545 and PI-2555, were obtained. These precursors are polyamic acids formed from the polycondensation reaction of pyromellitic dianhydride (PMDA) and oxydianiline (ODA),... 

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