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Available both as thermoplastic and thermosetresins, polyimides (PIs) are a family of someof the most heat- and fire-resistant polymersknown. Moldings and laminates are generallybased on thermoset resins, although some aremade from thermoplastic grades. Unlike mostplastics, polyimides are available as laminatesand shapes, molded parts, and stock shapesfrom some materials producers. Thin-film products— enamel, adhesives, and coatings — areusually derived from thermoplastic polyimideresins.
Polyimide parts and laminates can serve continuouslyin air at 260°C; service temperaturefor intermittent exposure can range from cryogenicto as high as 482°C. Glass-fiber-reinforcedversions retain over 70% of their flexuralstrength and modulus at 249°C. Creep is almostnonexistent, even at high temperatures, anddeformation under load (27.2 MPa) is less than0.05% at room temperature for 24 h.
These materials have good wear resistanceand low coefficients of friction, both of whichare further improved by polytetrafluoroethylenefillers. Self-lubricating parts containing graphitepowders have flexural strengths above 68MPa, which is considerably higher than thoseof typical thermoplastic bearing compounds.
Electrical properties of polymide moldingsare outstanding over a wide range of temperatureand humidity conditions.