Polyimides-heat resistance

In addition to carbon and glass fibers ia composites, aramid and polyimide fibers are also used ia conjunction with epoxy resias. Safety requirements by the U.S. Federal Aeronautics Administration (FAA) have led to the development of flame- and heat-resistant seals and stmctural components ia civiUan aircraft cabias. Wool blend fabrics containing aramids, poly(phenylene sulfide), EDF, and other inherently flame-resistant fibers and fabrics containing only these highly heat- and flame-resistant fibers are the types most frequently used ia these appHcations. 

The thermoset polyimides are a family of heat-resistant polymers with acceptable properties up to 260°C (500°F). They are unaffected by dilute acids, aromatic and ahphatic hydrocarbons, esters, ethers, and alcohols but are attacked by dilute alkahes and concentrated inorganic acids. 

The successful introduction of the polyimides stimulated attempts to produce somewhat more tractable materials without too serious a loss of heat resistance. This led to the availability of a polyamide-imides, polyester-imides and the polybismaleinimides, and in 1982 the polyether-imides. 

Excellent hydrolytic stability. (For example, PEK has very good resistance to hot water at 125°C, under which conditions other heat-resisting plastics such as the polyimides are liable to fail.)... 

Potyimides obtained by reacting pyromellitic dianhydride with aromatic amines can have ladder-like structures, and commercial materials are available which may be used to temperatures in excess of 300°C. They are, however, somewhat difficult to process and modified polymers such as the polyamide-imides are slightly more processable, but with some loss of heat resistance. One disadvantage of polyimides is their limited resistance to hydrolysis, and they may crack in aqueous environments above 100°C. 

Synthesis of PIQ. Very high heat resistance is required in order for a polymer film to be used as an insulator. This is because several heat treatments over 400 C are necessary in LSI interconnection and assembly processes. An aromatic polyimide (I), a reaction product of aromatic diamine and acid dianhydride, is one of the most heat resistant polymeric materials ... 

Influence of Water on Heat Resistance. It is known that the viscosity of polyimide prepolymer (polyamic acid solution) is reduced by the absorption of a-small amount of water(2). This is because the absorbed water reduces the molecular weight by hydrolysis. Therefore, it seems probable that absorbed water would reduce the heat resistance of cured PIQ film. For that reason, the influence of water contained in the starting materials on the heat resistance of cured PIQ film was investigated. 

High-performance polyimide-positive photosensitive heat resistance resins, (id, were prepared by Yamanaka et al. (3) and used in photosensitive compositions. 

Since the invention of integrated circuits (ICs), polyimides as heat-resistant organic polymers have been applied to insulation materials in electronics devices such as flexible printed circuit boards (FPCs), interlayer dielectrics, buffer coatings, and tape automated bonding (TAB). A polyimide thin layer is easily... 

To improve the solubility of polyimides, Korshak and co-workers used l,l-dichloro-2,2-bis(4-aminophenyl)-ethylene as the starting nucleophile [17] (Scheme 3.2). The resulting polymers turned out to be of relatively high molecular weight (r = 1.2-1.4 dl/g), heat resistant > 270 °C) and fire resistant (oxygen index (OI) = 36-39) (Table 3.2). Polypyromellitimide was soluble in H2SO4 only, but polyimides based on the dianhydrides of benzophenone-3,3, 4,4 -tetracarboxylic acid and diphenyloxide-3,3, 4,4 -tetracarboxylic acid were also soluble in w-cresol and a trichloroethane (TCE)/phenol (3 1) mixture. Diphenyloxide-3,3, 4,4 -tetracarboxylic acid was soluble even in N-methyl-2-pyrrolidone (NMP) (Scheme 3.2). 

The thermal stability of polyimides prepared from l,l-dichloro-bis(3-amino-4-chlorophenyl)-ethylene is lower than that of polyimides prepared with other 3,3 -diamino-4,4 -dichloroarylenes, in particular 3,3 -diamino-4,4 -dichlorobenzophenone. This suggests a negative effect of 1,1-dichloroethylene groups on thermal stability in these polymers. Based on softening temperatures, the heat resistance of polyimides with different dianhydride residues decreases in the series ... 

The effect of aromatic diamine residues on the heat resistance of polyimides is less clear cut. It was only by comparing thermomechanical curves of polypyromellitimides obtained from 3,3-diamino-4,4 -dichlorodiphenylmethane, and l,l-dichloro-2,2-di(3-amino-4-chlorophenyl)-ethylene that the system containing the 1,1-dichloroethylene group was found to be less heat resistant. With polyimides prepared from other dianhydrides this rule holds true as well but is less distinct. 

Aromatic bis(o-phenylendiamines) prepared from chloral derivatives, in particular 3,3, 4,4 -tetraminobenzophenone, were also used for the synthesis of polyimides possessing good solubilities in amide and phenolic solvents in combination with high thermal and heat resistance. In these respects, they were little different from polyimides formed from other bis(o-phenylendiamines) [29, 30]. 

Hence, heat resistance of the synthesised polyimides decreases with variation of the structure of the acid dianhydride fragment in the following order ... 

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,... 

It is customary to apply these polymers as the poly(amic -acids) and to dehydrate the film, coating, fiber or molded forms by heating to produce the polyimides. Polyimides are insoluble in most solvents hut are attacked by alkalies, ammonia and amines. These heat resistant polymers are used without fillers and with a graphite filler. 

This review article deals with aromatic polyimides that are processable from the melt or soluble in organic solvents. Conventional aromatic polyimides represent the most important family of heat resistant polymers, but they cannot be processed in the melt, and their application in the state of soluble intermediates always involves a hazardous step of cyclodehydration and elimination of a non-volatile polar solvent. A major effort has therefore been devoted to the development of novel soluble and/or melt-processable aromatic polyimides that can be applied in the state of full imidation. The structural factors conducive to better solubility and tractability are discussed, and representative examples of monomers showing favourable structural elements have been gathered and listed with the chemical criteria. Experimental and commercial aromatic polyimides are studied and evaluated by their solubility, transition temperatures and thermal resistance. An example is also given of the methods of computational chemistry applied to the study and design of polyimides with improved processability. 

Adrova N, Bessonov M, Laius LA,RudakovAP (1969) Polyimides a new class of heat-resistant polymers. IPST Press, Jerusalem... 

JP 05125345 (Japanese) 1993 Poly(vinyl butyral) blend adhesive composition for flexible printed circuit boards Ube Industries, Japan H Inoe, S Takabayashi, T Muramatsu, T Funakoshi Formulated resins having good flexibility and heat resistance are useful adhesives for polyimide/Cu foil laminated circuit boards Maleimide-terminated siloxane-imide block copolymers were formulated with poly(vinyl butyral) and melamine resins to give adhesive compositions. 

JP 05306386 (Japanese) 1993 Heat-resistant adhesive composition Ube Industries, Japan H Inoe, S Takabayashi, T Muramatsu, T Hirano Resin formulation useful for bonding Cu foils to polyimide films for electronic applications Heat-resistant adhesives were formulated to include imide-siloxanes with softening points <300° C. Diaminopolysiloxanes and aromatic amines were used maleimide termination also utilized. 

JP 05311144 (Japanese) 1993 Heat-resistant adhesive compositions containing polyimide-siloxane block copolymers Ube Industries, Japan H Inoe, S Takabayashi, T Funakoshi, K Sonoyana Useful for Cu-clad laminates of printed circuit boards and tape-automated bonding with good flexibility and heat resistance Formulated compositions containing siloxane-imide block copolymers made from aromatic tetracarboxylic acids and aromatic diamines and aminosiloxanes... 

JP 62246978 (Japanese) 1987 Heat-resistant adhesives containing siloxanes and imide-containing resins Shin-Etsu Chemical Industry Co. Ltd., Japan S Ueno, N Nakanishi, S Hoshida Adhesives showed good adhesion and flexibility useful in the preparation of flexible laminates Resin was prepared from the reaction product of bismaleimides, diamines, amino-terminated siloxanes and a bisphenol A cyanate adduct. The adhesive formulation was used on polyimide films... 

Inoue H Takabayash S Muramatsu T, Funagoshi T, Hirano T. Polyimide-siloxane block copolymer-based heat-resistant adhesive compositions. US Patent 5180627 A 930119 11 pp... 

A similar concept based on a mixture of BMI-MDA (Matrimide 5292 A) and bis-alkenylphenol (Matrimide 5292 B) with a flexible polyimide has been patented as a heat-resistant adhesive [117]. 

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