Polyetheretherketones (PEEK) are also referred to as polyketones. The most common structure is given in Figure 12.1.

PEEK is a thermoplastic with extraordinary mechanical properties. The Young’s modulus of elasticity is 3.6GPa and its tensile strength is 170MPa. PEEK is partially crystalline, melts at around 350°C, and is highly resistant to thermal degradation. The material is also resistant to both organic and aqueous environments, and is used in bearings, piston parts, pumps, compressor plate valves, and cable insulation applications. It is one of the few plastics compatible with ultrahigh vacuum applications. In summary, the properties of PEEK include:

Polyethersulfone (PES) is an amorphous polymer and a high-temperature engineering thermoplastic. Even though PES has high-temperature performance, it can be processed on conventional plastics processing equipment. Its chemical structure is shown in Figure 12.2. PES has an outstanding ability to withstand exposure to elevated temperatures in air and water for prolonged periods.

Because PES is amorphous, mold shrinkage is low and is suitable for applications requiring close tolerances and little dimensional change over a wide temperature range. Its properties include:

Polyphenylene sulfide (PPS) is a semicrystalline material. It offers an excellent balance of properties, including high-temperature resistance, chemical resistance, flowability, dimensional stability, and electrical characteristics. PPS must be filled with fibers and fillers to overcome its inherent brittleness. Because of its low viscosity, PPS can be molded with high loadings of fillers and reinforcements. Because of its outstanding flame resistance, PPS is ideal for high-temperature electrical applications. It is unaffected by all industrial solvents. The structure of PPS is shown in Figure 12.3.

There are several variants to regular PPS that may be talked about by suppliers or may be seen in the literature. These are:

PPS properties are summarized:

Polysulfone (PSU) is a rigid, strong, tough, high-temperature amorphous thermoplastic. The structure of PSU is shown in Figure 12.4.

Its properties summarized:

Polyphenylsulfone (PPSU) is a rigid, strong, tough, high-temperature amorphous thermoplastic. It has a high heat deflection temperature of 405°F (207°C); it can withstand continuous exposure to heat and still absorb tremendous impact without cracking or breaking. It is inherently flame retardant and offers exceptional resistance to bases and other chemicals. The structure of PPSU is shown in Figure 12.5.

Its properties summarized:

Polybenzimidazole (PBI) is a unique and highly stable linear heterocyclic polymer. The chemical structure is shown in Figure 12.6. PBI exhibits excellent thermal stability, resistance to chemicals, acid and base hydrolysis, and temperature resistance. PBI can withstand temperatures as high as 430°C, and in short bursts, to 760°C. PBI does not burn and maintains its properties as low as −196°C.

Ideally suited for its application in extreme environments, PBI can be formed into stock shapes and subsequently machined into high precision finished parts. Since PBI does not have a melt point, moldings from virgin PBI polymer can only be formed in a high-temperature, high-pressure compression molding process.

PBI is highly resistant to deformation, and has low hysteresis loss and high elastic recovery. PBI exhibits ductile failure, and may be compressed to over 50% strain without fracture. Celazole® PBI has the highest compressive strength of any thermoplastic or thermosetting resin at 400MPa. There is no weight loss or change in compressive strength of Celazole® PBI exposed to 260°C in air for 500 hours. At 371°C, no weight or strength change takes place for 100 hours. In spite of these unusual properties, PBI is usually blended with other plastics, particularly polyesters and PEEK.