2012: Advent Chemistry: Teflon

by on December 15, 2012

Well, we’ve done a couple of entries on medicines, so let’s go back to some more fundamental chemistry and look at a polymer.

The repeat unit of teflon, shown in parentheses with an 'n' to indicate that it is part of a polymer.

This here is a section of polytetrafluoroethylene, or Teflon as it’s better known. It’s a fairly ordinary polymer in chemical terms, except for the extremely hydrophobic (water-hating) nature of its surface, which makes Teflon as slippery as wet ice against wet ice.

Polymers are interesting things. Technically speaking, biological molecules like DNA and proteins are polymers, and cellulose certainly is. A polymer is a large molecule made up of many identical sections, or a combination of several different repeating sections. The basic building block of a polymer is its “repeat unit”, the smallest section that can be multiplied to get the whole. This is on the same principle that sodium chloride, which actually forms huge crystals, is called NaCl and not Na10000Cl10000 – it’s simpler.

The repeat unit of Teflon is tetrafluoroethylene – two carbons with a double bond between them, and two fluorines bonded to each carbon. But the polymer has no double bonds in it, so how can that be right?

Polymers are named after the structure of the thing you start with to get them. These “monomers” react with each other to give a polymer, which literally means “many mers”. “Mer” is of course a technical science word meaning “thing”. Teflon is a perfect example of one of the simplest kinds of polymer, one formed by addition polymerisation. The double bonds open up and link together, like a group of people going from standing with their arms crossed to holding hands. Addition reactions are the main thing that alkenes – double-bonded carbons – do, and not doing addition reactions is one of the major differences between an aromatic ring and ordinary double bonds.

Incidentally, how Teflon sticks to the pan really is one of the great mysteries of chemistry. It doesn’t make sense for pure Teflon to stick well to metal, so we assume that, at least in the good quality pans, there’s something besides just tetrafluoroethylene going into the polymer. The only people who know for sure are the intellectual property holders DuPont, and they aren’t telling.

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