The Polyimides

If most plastics are summer materials (happy at room temperature, nervous near a stove), the polyimides are the family that thrives where others melt, char, or simply give up. Their secret is a backbone built almost entirely from rings: stiff aromatic rings alternating with the five-membered imide ring, locked into a chain so rigid and thermally stable that some polyimides don’t have a meltable state at all. They just keep working, cheerfully, at temperatures that would reduce ordinary plastics to smoke.

This is the family you call when the environment is genuinely hostile. Polyimides insulate the wiring in jet engines and spacecraft, form the flexible amber film in the circuit boards folded inside your phone, and stand in for metal in bushings and seals that run too hot for anything softer. Their close relatives, polyamide-imides, polyetherimides, and the almost absurdly heat-proof polybenzimidazole (which was developed with space and firefighting in mind), trade a little of that extreme performance for easier processing, filling out a whole tier of high-performance engineering polymers. The price of all this toughness is that polyimides are difficult and expensive to make and shape; the rigidity that makes them invincible also makes them stubborn.

The polyimides are the family that answers the question every other plastic dreads: what do you use when even the good plastics aren’t good enough?