Polyimides PI

Polyimides (PI) are finding increasing application as high-performance, high-temperature polymeric composites in high-speed commercial aircraft. 

The thermo-oxidative degradation of PI is also possible at the expense of the benzene rings involved in the polymer chain. This is confirmed hy the oxidation of these rings in an oxygen atmosphere of 340 °C [12], and the introduction of substituents reduces considerably the thermal stability of the aromatic rings. 

The abstraction of a hydrogen atom from the benzene ring during the oxidation of PI may cause the formation of water, the presence of which promotes the development of autocatalytic random heterolytic processes of degradation of the polymer chain 

The occurrence of inter-chain crosslinking due to the interaction of two phenyl radicals is a further important indication of the abstraction of a hydrogen atom from the benzene ring. This is confirmed by the greater rate of polymer crosslinking in the 

The manner of degradation of PI in the solid phase has several peculiarities. In particular, it has been shown [13] that the decomposition rate of PI in inert and oxidative atmospheres decreases with increasing film thickness. These differences are considered to be associated with specific features in the supermolecular structure of thin and thick polyimide films. 

These plastics offer the most unique combinations of properties available for use in industrial service. The plastics are usable from -190°C to 370°C. These excellent low temperature properties are often overlooked where a plastic is required to retain some ductihty and toughness at such low temperatures. Some combinations of the resins can be taken to 510°C for short periods without destroying the parts. The plastic has excellent creep and abrasion resistance, excellent elastic modulus for a thermoplastic, and good tensile strength that does not drop off rapidly with temperature. The chemical resistance must be rated as good. 

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Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

Other Polymers. Besides polycarbonates, poly(methyl methacrylate)s, cycfic polyolefins, and uv-curable cross-linked polymers, a host of other polymers have been examined for their suitabiUty as substrate materials for optical data storage, preferably compact disks, in the last years. These polymers have not gained commercial importance polystyrene (PS), poly(vinyl chloride) (PVC), cellulose acetobutyrate (CAB), bis(diallylpolycarbonate) (BDPC), poly(ethylene terephthalate) (PET), styrene—acrylonitrile copolymers (SAN), poly(vinyl acetate) (PVAC), and for substrates with high resistance to heat softening, polysulfones (PSU) and polyimides (PI). 

Polyimides (PI) are polycondensation products (1) prepared from derivatives of tetracarboxylic acids and primary diamines (1—5). Descriptions of self-polycondensation polymers (2) based on aminodicarboxylic acid derivatives are also found in the literature (6—9). 

Solution blending Polar as well as nonpolar solvents can be used in this method. The polymer is solubilized in a proper solvent and then mixed with the filler dispersion. In solution, the chains are well separated and easily enter the galleries or the layers of the fillers. After the clay gets dispersed and exfoliated, the solvent is evaporated usually under vacuum. High-density polyethylene [24], polyimide (PI) [25], and nematic hquid crystal [26] polymers have been synthesized by this method. The schematic presentation is given in Scheme 2.2. 

Over the last decade, selected papers1114 have examined the deposition of fluoropolymers, using RF magnetron sputtering. All of these papers have examined the deposition of PTFE, with some of them2314 also studying the deposition of polyimide (PI) films. This chapter extends these studies and will report on the sputter deposition behavior of PTFE (polytetrafluoroethylene), PVDF (polyvinylidenefluoride), and FEP (fluorinated ethylene propylene copolymer) films. 

Information gathering Polyimide (PI) is made by reacting an aromatic dianhydride (DAN) with an aromatic diamino ether (DA), Fig. 21.18, or more simply,... 

Interpretation of these curves show that Poly (vinyl chloride) (PVC) first loses HC1 later the mixture of unsaturated carbon-carbon backbone and unchanged poly (vinyl chloride) partly degrades to small fragments. Poly (methyl methacrylate) (PMMA), branched polyethylene (HPPE), and polytetrafluorethylene (PTFE) degrade completely to volatile fragments, while a polyimide (PI) partially decomposes, forming a char above 800°C. 

Imides - Polyimides (PI) have been conventionally prepared by the chemical or thermal cyclodehydration of polyamic acids formed from the solution reaction of aromatic tetracarboxylic dianhydrides and aromatic diamines. The early PI were insoluble and relatively intractable. The polyamic acid was the processable intermediate. However, the polyamic acid precursor has two major shortcomings, hydrolytic instability and the evolution of volatiles during the thermal conversion to PI. In addition, residual solvent was left in adhesive tapes and prepregs to obtain tack, drape and flow. During the fabrication of components, the evolution of volatiles caused processing problems and led to porosity in the part. As work progressed on PI, other synthetic routes were investigated (e.g. reaction of esters of aromatic tetracarboxylic acids with diamines... 

Figure 18. Depth profiles of hydrogen from polyimide (PI) implanted with 100 keV Kr ions to the fluences indicated. The horizontal line shows the hydrogen concentration in pristine PI. The profiles were determined from ERDA measurement performed with 2 MeV alpha particles [122]. The depth resolution was about 50 nm. It is seen that significant H depletion starts at the fluence of about IxlO " cm. ...

Figure 20. AFM deflection images of pristine polyimide (PI) and PI implanted with 90 keV N ions to fluences indicated [127],...

The increasing importance of multilevel interconnection systems and surface passivation in integrated circuit fabrication has stimulated interest in polyimide films for application in silicon device processing both as multilevel insulators and overcoat layers. The ability of polyimide films to planarize stepped device geometries, as well as their thermal and chemical inertness have been previously reported, as have various physical and electrical parameters related to circuit stability and reliability in use (1, 3). This paper focuses on three aspects of the electrical conductivity of polyimide (PI) films prepared from Hitachi and DuPont resins, indicating implications of each conductivity component for device reliability. The three forms of polyimide conductivity considered here are bulk electronic ionic, associated with intentional sodium contamination and surface or interface conductance. 

The chemical structures of thermosets are generally much more diverse than the commodity thermoplastics. The most common types of thermosets are the phenol-formaldehydes (PF), urea-formaldehydes (UF), melamine-formaldehydes (MF), epoxies (EP), polyurethanes (PU), and polyimides (PI). Appendix 2 shows the chemical structure of these important thermosetting polymers. 

A closely related phenomenon induced by linearly polarized light was found independently by Gibbons et al., who employed a polyimide (PI) film doped with azobenzene molecules as a dichroic dye and showed that the direction of homogeneous... 

Polyimide (PI) caps all other polymers in its temperature range of use (-200 to 260 °C in air short-time even up to 500 °C). Because of its high price, it is used in special cases only, such as space vehicles, nuclear reactors and some electronic parts. Newer developments, related to polyimide, are the polyether imides (e.g. Ultem ), polyester imides and polyamide imides (e.g. Torlon ), all with very good mechanical, thermal and electrical properties and self-extinguishing. 

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