Kapton
Kapton is a polyimide film developed by DuPont in the late 1960s that remains stable across a wide range of temperatures, from −269 to +400 °C (−452 to 752 °F; 4–673 K). Kapton is used in, among other things, flexible printed circuits (flexible electronics) and thermal blankets used on spacecraft, satellites, and various space instruments.
The chemical name for Kapton K and HN is poly (4,4'-oxydiphenylene-pyromellitimide). It is produced from the condensation of pyromellitic dianhydride and 4,4'-oxydiphenylamine. Kapton synthesis is an example of the use of a in step polymerization. The intermediate polymer, known as a "poly(amic acid)", is soluble because of strong hydrogen bonds to the polar solvents usually employed in the reaction. The ring closure is carried out at high temperatures (200–300 °C, 473–573 K).
The thermal conductivity of Kapton at temperatures from 0.5 to 5 Kelvin is rather high for such low temperatures, κ = 4.638×10−3T0.5678 W·m−1·K−1. This, together with its good dielectric qualities and its availability as thin sheets have made it a favorite material in cryogenics, as it provides electrical insulation at low thermal gradients. Kapton is regularly used as an insulator in ultra-high vacuum environments due to its low outgassing rate.
Kapton-insulated electrical wiring has been widely used in civil and military aircraft because it is lighter than other insulators and has good insulating and temperature characteristics. For these reasons, the sunshield of the James Webb Space Telescope will be made of it.
However, Kapton insulation ages poorly: an FAA study shows degradation in under 100 hours in a hot, humid environment. It was found to have very poor resistance to mechanical wear, mainly abrasion within cable harnesses due to aircraft movement. Many aircraft models have had to undergo extensive rewiring modifications—sometimes completely replacing all the Kapton-insulated wiring—because of short circuits caused by the faulty insulation. Kapton-wire degradation and chafing due to vibration and heat has been implicated in multiple crashes of both fixed wing and rotary wing aircraft, with loss of life.
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