PTFE is similar to poly(ethene) in its structure, in that it has a long carbon chain 'backbone', but the original monomer is CF2=CF2. The repeating unit and chain are shown below, and a structural representation of the PTFE chain is shown at the top of all my pages.
PTFE has many remarkable properties that are put to use in a wide variety of industries. It shows excellent chemical inertness and solvent resistance, extreme heat resistance and meling point and outstanding frictional properties.
Its chemical inertness is largely as a result of its strucure and bonding, and of steric factors. Compare the sizes of fluorine and carbon atoms (Van der Waal's radii) with the carbon-fluorine bond length in the table below. The ratio allows the fluorine atoms to lie close to the carbon chain. When the distance between adjacent fluorine atoms (bonded to the same carbon atom) is considered alongside fluorine's Van der Waal's radius it is clear that the fluorine atoms form a complete sheath around the carbon chain. As a result of these factors the C-F bond is very strong and attacking the carbon backbone is virtually impossible, so the PTFE chain is very stable. As the forces between the chains are also strong, PTFE is insoluble in most solvents.
| Bond or Distance | Value / pm | Source |
|---|---|---|
| C-F bond | 138 | reference 6 |
| F-F (adjacent, bonded to same C atom) | 217 | reference 6 |
| C (Van der Waal's radius) | 170 | reference 7 |
| F (Van der Waal's radius) | 147 | reference 7 |
While the Fluorine atoms in the PTFE chain have a strong affinity for other PTFE fluorines they will repel any other atoms/molecules giving PTFE its famous 'non-stick' properties (coefficient of friction: 0.12-0.15 static, 0.05-0.1 dynamic. Source: www.dupont.com). It was this property that made Teflon(R) a household name with its use in frying pans.
Another reason why PTFE is well suited to use on frying pans is its heat resistance. With a melting point of 327oC, no PTFE is going to end up in your fried egg...
So PTFE or similar fluorinated polymers have been used in just about any extreme condition you can think of. From NASA's spacecraft to gaskets and seals on high performance machinery, PTFE's properties have been widely exploited.
Teflon(R) is a registered trademark of E.I. du Pont de Nemours and Co.
Tom Westgate - cha99tdw@sheffield.ac.uk (document modification date: 24th May 2000)