High-Temperature and Fire-Resistant Polymers

In this chapter, attention is focused on a number of polymers that are either themselves characterized by special properties or are modified for special uses. These include high-temperature and fire-resistant polymers, electroactive polymers, polymer electrolytes, liquid crystal polymers (LCPs), polymers in photoresist applications, ionic polymers, and polymers as reagent carriers and catalyst supports. 

Polyimides (Pis) were the first so-called high-heat-resistant plastics. They in fact retain a significant portion of their room-temperature mechanical properties from - 240 to 315°C (-400 to +600°F) in air. Pis, which are available in both TPs and TSs, are a family of some of the most heat- and fire-resistant polymers known. As discussed in connection with some of the other polymers, there are others that have heat resistance in the 260°C (500°F) range. 

Liquid Crystal Polymers Thermoplastic aromatic copolyesters with highly ordered structure. Has good tensile and flexural properties at high temperatures, chemical, radiation and fire resistance, and weatherabil-ity. Processed by sintering and injection molding. Used to substitute ceramics and metals in electrical components, electronics, chemical apparatus, and aerospace and auto parts. Also called LCP. 

Polyethersulfone Thermoplastic aromatic polymer has good heat and fire resistance, transparency, dielectric properties, dimensional stability, rigidity, and toughness, but poor solvent and stress cracking resistance, processibility, and weatherability. Processed by injection, blow, and compression molding and extrusion. Used in high temperature applications, electrical devices, medical devices, housings, and aircraft and auto parts. Also called PES. 

Polyphthalamide Thermoplastic polymer of aromatic diamine andphthalic anhydride. Has good heat, chemical, and fire resistance, impact strength, retention of properties at high temperatures, dielectric properties, and stiffness, but decreased light resistance and poor processability. Processed by solution casting, molding, and extrusion. Used in films, fibers, and molded parts. Also called PPA. 

Obtained copoly and block-copolyestersulfoneketones, as well as polyaiylates based of dichloranhydrides of phthalic acids and chloranhy-dride of 3,5-dibromine- -oxybenzoic acid and copolyester with groups of terephthaloyl-bis(w-oxybenzoic) acid possess high mechanical and dielectric properties, thermal and fire resistance and also the chemical stability. The regularities of acceptor-catalyst method of polycondensation and high-temperature polycondensation when synthesizing named polymers have been studied and the relations between the composition, structure and properties of polymers obtained have been established. The synthesized here block-copolyesters and copolyesters can find application in various fields of modem industry (automobile, radioelectronic, electrotechnique, avia, electronic, chemical and others) as thermal resistant constmction and layered (film) materials. 

After the tragedy of Apollo 1, NASA intensified its focus on advanced fire-resistant materials and one of the first alternatives considered was PBI. NASA contracted with Celanese Corporation to develop a line of PBI textiles for use in space suits and vehicles. Heat and flame resistant PBI fabric based on the fiber for high-temperature applications was developed. The fibers developed from the PBI polymer showed a number of highly desirable features, such as inflammability, no melting point, and retention of both strength and flexibility after exposure to flames. The stiff fibers also maintained their integrity when exposed to high temperatures and were mildew, abrasion and chemical resistant. 

PHB is a unique sample of a moderate hydrophobic polymer being biocompatible and biodegradable at both high melting and crystallization temperatures. However, its strength and other characteristics, such as thermal stability, gas permeability, and both reduced solubility and fire resistance, are insufficient for its large-scale application. 

Applications for PEEK in the aerospace industry include critical engine parts as the polymer can withstand high temperatures and the tribological interaction of dry and lubricated material contacts. In aircraft exterior parts, PEEK provides excellent resistance to rain erosion, while for aircraft interior components, its inherent flame letardancy and low smoke and toxic gas emission reduce hazard in the event of a fire. In aircraft electrical systems, the polymer is used for manufacture of convoluted tubing to protect wires and fibre optic filaments. PEEK is also used to protect the wire harnesses used in commercial aircraft engines. 

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