Tuesday, November 04, 2014

How many polymers are there?

It was suggested in another social media site this last weekend that the big chemical companies have tucked away in their vaults the results of polymerizing "...every molecule with a double bond has been treated with a free radical initiator, and every difunctional molecule has been tested as well." To which I say hogwash.

Let me give a hint as to the magnitude of the polymer world. Let's start with something simple like making a polyurethane. This is a "simple" case because the stoichiometry is pretty limited. You usually try to have an equivalent amount of isocyanate groups and hydroxyl groups (or something close to 1:1). We'll get into crazy stoichiometry in a minute. And for no particular reason other than the breadth of their offerings, let's look at all the isocyanates offered by Bayer and all the polyols offered by Perstorp. (There are lots of other suppliers of isocyanates and polyols - I'm making no particular endorsement here of any kind.) If my counting is correct, Bayer has 135 commercial isocyanate offerings and Perstorp has 34 commercial caprolactone based polyols. Just pairing each isocyanate with each polyol would results in 135 x 34 = 4,590 polymers. To further complicate matters however, sometimes 2 isocyanates are used, as are 2 polyols. So now you can have 135 x 134 x 34 = 615,060 OR 135 x 34 x 33 = 151,470 or even 135 x 134 x 34 x 33 = 20,296,980. All told that is 4590 + 615060 + 151470 + 20296980 = 21,068,100 polymers using the materials from just these 2 companies.

Now let's go for the really big numbers. Consider alkyl (meth)acrylates, a nice subsection of unsaturated compounds but by no means all the options available. Alkyl (meth)acrylates are available between methyl (C1) and at least dodecyl (C12), and the acids are nice to have as a weapon too. So that is 26 monomers available. My personal experience is that I've seen as many as 6 (meth)acrylate monomers used. That means there are 26 homopolymers, 26 x 25 = 650 copolymers, 26 x 25 x 24 = 15,600 terpolymers, 26 x 25 x 24 x 23 = 358,800 tetrapolymers, 26 x 25 x 24 x 23 x 22 = 7,893,600 pentapolymers and 26 x 25 x 24 x 23 x 22 x 21 = 165,765,600 hexapolymers potentially available for just alkyl (metha)acrylates. All told, that is 174,034276 alkyl (meth)acrylates.

But that number would rapidly be dwarfed if we included any of the common options available when polymerizing acrylates, such as
  • their ability to be used in pretty much any ratio (I've seen cases where changing one monomer by as little as 2 percentage points make a big difference in the final properties)
  • the concentration of the initiator (which alters molecular weight)
  • chain transfer agents (which also alter molecular weight)
  • reaction conditions (bulk, UV-initiated, thermal-initiated, solution, emulsion) all which have tremendous influence on the final product

Over 174 million polymers! If you had a machine setting up 1 reaction a second 24/7/365, that is still 5 1/2 years or solid work. And setting up the reaction is the easy part. You would still need to initiate the polymerization and (potentially) keep it going. And you still wouldn't be even close to the end of what polymers are available.

So how many polymers are there? I have no idea, but it is a tremendous number. It reminds me of the old joke of a young person looking at a starlit sky and asking an older person how many stars are out there. The answer: "All of them".

Previous Years

November 4, 2013 - Who's Been Eating My Ocean Plastic?

November 4, 2010 - Plastics in the "Economist"

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