Polyimides

Normally infusible, coloured (often amber) high performance polymers with predominantly aromatic molecules of high thermal stability. Semi-fabricated shapes are usually supplied by the polymer manufacturer and made by powder sintering or working with more tractable pre-cursors and completing polymerization in final form, though some melt-process able grades of resin are manufactured.

They have excellent high temperature properties and radiation resistance, inherently low flammability and smoke emission, low creep and high wear resistance and are very expensive. They have moderately high water absorption and are prone to hydrolysis and attack by alkalis and concentrated acids.


General Properties :
Chemical Resistance
Acids – concentrated Poor
Acids – dilute Fair
Alcohols Poor
Alkalis Poor
Aromatic hydrocarbons Good
Greases and Oils Good
Halogenated Hydrocarbons Good
Halogens Fair
Ketones Good
Electrical Properties
Dielectric constant @1MHz 3.4
Dielectric strength ( kV mm-1 ) 22
Dissipation factor @ 1kHz 0.0018
Surface resistivity ( Ohm/sq ) 10 16
Volume resistivity ( Ohmcm ) 10 18
Mechanical Properties
Coefficient of friction 0.42
Elongation at break ( % ) 08 to 70
Hardness – Rockwell E52 to 99
Izod impact strength ( J m -1 ) 80
Tensile modulus ( GPa ) 2.0 to 3.0
Tensile strength ( MPa ) 70 to 150
Physical Properties
Density ( g cm-3 ) 1.42
Flammability V0
Limiting oxygen index ( % ) 53
Radiation resistance Good
Refractive index 1.66
Resistance to Ultra-violet Poor
Water absorption – over 24 hours ( % ) 0.2 to 2.9
Thermal Properties
Coefficient of thermal expansion ( x10-6 K-1 ) 30 to 60
Heat-deflection temperature – 1.8MPa ( C ) 360
Lower working temperature ( °C ) -270
Specific heat ( J K-1 kg-1 ) 1090
Thermal conductivity @23C ( W m-1 K-1 ) 0.10 to 0.35
Upper working temperature ( C ) 250 to 320

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