Polyimide temperature

Polyimide Temperature (°C) Feed pressure (atm) Pip2) PiCO ) alOj/Nj) alCOj/Nj) a(C02/CH4) Reference... 

This polymerization is carried out in the two stages indicated above precisely because of the insolubility and infusibility of the final product. The first-stage polyamide, structure [IX], is prepared in polar solvents and at relatively low temperatures, say, 70°C or less. The intermediate is then introduced to the intended application-for example, a coating or lamination-then the second-stage cyclization is carried out at temperatures in the range 150-300°C. Note the formation of five-membered rings in the formation of the polyimide, structure [X], and also that the proportion of acid to amine groups is 2 1 for reaction (5.II). 

Polyimides for use ia molded products and high temperature films can be produced by the reaction of pyromelHtic dianhydride [89-32-7] and 4,4 -diaminodiphenyl ether [13174-32-8] ia DMAC to form a polyamide that can be converted iato a polyimide (13). DMAC can also be used as a spinning solvent for polyimides. AdditionaUy, polymers containing over 50% vinyHdene chloride are soluble up to 20% at elevated temperatures ia DMAC. Such solutions are useful ia preparing fibers (14). 

Polyimide. Polyimide is a biaxiaHy oriented high performance film that is tough, flexible, and temperature- and combustion-resistant. Its room temperature properties compare to poly(ethylene terephthalate), but it retains these good characteristics at temperatures above 400°C. Its electrical resistance is good and it is dimensionally stable. The principal detriment is fairly high moisture absorbance. The main uses are for electrical insulation, particularly where high temperatures are prevalent or ionizing radiation is a problem. The films may be coated to reduce water absorption and enhance... 

Miscellaneous Applications. Ben2otrifluoride derivatives have been incorporated into polymers for different appHcations. 2,4-Dichloroben2otrifluoride or 2,3,5,6-tetrafluoroben2otrifluoride [651-80-9] have been condensed with bisphenol A [80-05-7] to give ben2otrifluoride aryl ether semipermeable gas membranes (336,337). 3,5-Diaminoben2otrifluoride [368-53-6] and aromatic dianhydrides form polyimide resins for high temperature composites (qv) and adhesives (qv), as well as in the electronics industry (338,339). 

The process known as transimidization has been employed to functionalize polyimide oligomers, which were subsequentiy used to produce polyimide—titania hybrids (59). This technique resulted in the successhil synthesis of transparent hybrids composed of 18, 37, and 54% titania. The effect of metal alkoxide quantity, as well as the oligomer molecular weight and cure temperature, were evaluated using differential scanning calorimetry (dsc), thermogravimetric analysis (tga) and saxs. 

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. 

Polyimides of 6FDA and aUphatic diamines with good low temperature processkig and low moisture swelling are known to be useful as hot-melt adhesives (109). Aluminum strips bonded by this polymer (177°C/172 kPa (25 psi) for 15 min) exhibited a lap-shear strength of 53 MPa (7690 psi) at room temperature and 35 MPa (5090 psi) at 100°C. The heat- and moisture-resistant 6F-containing Pis useful ki electronic devices are prepared from... 

The newer open-ceU foams, based on polyimides (qv), polyben2imida2oles, polypyrones, polyureas, polyphenylquinoxalines, and phenoHc resins (qv), produce less smoke, are more fire resistant and can be used at higher temperatures. These materials are more expensive and used only for special appHcations including aircraft and marine vessels. Rigid poly(vinyl chloride) (PVC) foams are available in small quantities mainly for use in composite panels and piping appHcations (see Elame retardants Heat-RESISTANTPOLYA rs). 

Polyimide and Melamine. These are both low density, essentially open-ceU foams used as pipe insulations, particularly those involved with fluids operating at temperatures up to 530 K. Because these foams operate at higher temperatures and have improved flammabiHty characteristics compared to other foams, they are also used for some aircraft and marine appHcations. 

Carboxyhc acids react with aryl isocyanates, at elevated temperatures to yield anhydrides. The anhydrides subsequently evolve carbon dioxide to yield amines at elevated temperatures (70—72). The aromatic amines are further converted into amides by reaction with excess anhydride. Ortho diacids, such as phthahc acid [88-99-3J, react with aryl isocyanates to yield the corresponding A/-aryl phthalimides (73). Reactions with carboxyhc acids are irreversible and commercially used to prepare polyamides and polyimides, two classes of high performance polymers for high temperature appHcations where chemical resistance is important. Base catalysis is recommended to reduce the formation of substituted urea by-products (74). 

For many moderate-duty films for operating temperatures below 80 to 120°C, M0S2 is used in combination with acryflcs, alkyds, vinyls, and acetate room temperature curing resins. For improved wear life and temperatures up to 150—300°C, baked coatings are commonly used with thermosetting resins, eg, phenohcs, epoxies, alkyds, siUcones, polyimides, and urethanes. Of these, the MlL-L-8937 phenoHc type is being appHed most extensively. 

The dianhydride of 1,4,5,8-naphthalene tetracarboxyhc acid [81-30-1] has been of research interest for the preparation of high temperature polymers, ie, polyimides. The condensation of the dianhydride with o-phenylenediamines gives vat dyes and pigments of the benzimidazole type. 

Possible tape materials include polyimide, polyester, polyethersulfone (PES), and polyparabanic acid (PPA) (18). Of these, polyimide is the most widely used material because its high melting point allows it to survive at temperatures up to 365°C. Although polyester is much cheaper than other materials, its use is limited to temperatures less than 160°C. PES and PPA, on the other hand, are half as cosdy as polyimide, and can survive maximum short-term temperatures of 220 and 275°C, respectively. PES has better dimensional stabiUty than polyimide, absorbs less moisture, and does not tear as easily however, it is inflammable and can be attacked by certain common solvents. Table 7 Hsts various plastic tapes and their properties. Common bump materials are gold, copper, and 95% Pb/5% Sn solder (see Tables 6 and 8 for properties see also References 2 and 21). 

Thermosetting-encapsulation compounds, based on epoxy resins (qv) or, in some niche appHcations, organosiHcon polymers, are widely used to encase electronic devices. Polyurethanes, polyimides, and polyesters are used to encase modules and hybrids intended for use under low temperature, low humidity conditions. Modified polyimides have the advantages of thermal and moisture stabiHty, low coefficients of thermal expansion, and high material purity. Thermoplastics are rarely used for PEMs, because they are low in purity, requHe unacceptably high temperature and pressure processing conditions. 

Carbon—Carbon Composites. Above 300°C, even such polymers as phenoHcs and polyimides are not stable as binders for carbon-fiber composites. Carbon—carbon composites are used at elevated temperatures and are prepared by impregnating the fibers with pitch or synthetic resin, foUowed by carbonization, further impregnation, and pyrolysis (91). 

Since successful commercialization of Kapton by Du Pont Company in the 1960s (10), numerous compositions of polyimide and various new methods of syntheses have been described in the Hterature (1—5). A successful result for each method depends on the nature of the chemical components involved in the system, including monomers, intermediates, solvents, and the polyimide products, as well as on physical conditions during the synthesis. Properties such as monomer reactivity and solubiHty, and the glass-transition temperature,T, crystallinity, T, and melt viscosity of the polyimide products ultimately determine the effectiveness of each process. Accordingly, proper selection of synthetic method is often critical for preparation of polyimides of a given chemical composition. 

The two-step poly(amic acid) process is the most commonly practiced procedure. In this process, a dianhydride and a diamine react at ambient temperature in a dipolar aprotic solvent such as /V,/V-dimethy1 acetamide [127-19-5] (DMAc) or /V-methy1pyrro1idinone [872-50-4] (NMP) to form apoly(amic acid), which is then cycHzed into the polyimide product. The reaction of pyromeUitic dianhydride [26265-89-4] (PMDA) and 4,4 -oxydiani1ine [101-80-4] (ODA) proceeds rapidly at room temperature to form a viscous solution of poly(amic acid) (5), which is an ortho-carboxylated aromatic polyamide. 

Diesters of Tetracarboxylic Acids with Diamines. Dianhydrides react with alcohols at a moderate temperature, producing the tetracarboxyhc acid diesters. Ben2ophenonetetracarboxyhc acid diester (BTTA diester) is obtained from B I DA as a mixture of three positional isomers. Partiy because it is an isomeric mixture, the diester of BTTA is soluble in methanol at high concentrations. A state-of-the-art thermoset polyimide,... 

Table 2. Properties of High Temperature Polyimide Films...

---