The discovery of Teflon

Teflon (poly(tetrafluoroethene), ptfe) was discovered by accident though the story of its discovery does recall the phrase 'chance favours the prepared mind'. In 1938, 26-year old Roy Plunkett was working for DuPont on gases which could be used as coolants in fridges, one of which was tetrafluoroethene. 

On 6 April he opened the valve of a cylinder containing about 1kg of the gas but nothing came out. He did what many of us would do and poked the valve with a wire but to no avail. He then weighed the cylinder and the weight indicated that it was still full. When he shook the cylinder it rattled. Eventually he sawed open the cylinder to find that it contained a solid. Somehow, the gas molecules, which each have a carbon-carbon double bond, had polymerised. 

Because this is an addition polymer, no other reactant is needed. No one seems to have a clear explanation about what caused the spontaneous polymerisation.

Teflon is chemically inert (because it is saturated and has only strong C-C and C-F bonds) and very slippery. Its best known use is as the coating of non-stick pans. It is also said that the US space programme would have floundered without Teflon because the material was used to make so many things, from space suits to the bags used to hold samples of moon rock.

During the Manhattan Project which produced the first atomic bomb, Teflon was used for valves and gaskets that would resist chemical attack by the highly reactive uranium hexafluoride. This compound was used to separate the isotopes ²³⁵U (which is fissile and can be used as a fuel) and ²³⁸U (which is not) by gaseous diffusion. Uranium hexafluoride is unusual for a metal salt because it is volatile, becoming a gas at 56°C. The lighter ²³⁵UF₆ gas diffuses through a porous barrier faster than ²³⁸UF₆ and this was used as the basis of the separation method.