Thursday, May 13, 2010

Airborne Polymers

Polymers are never thought of as being airborne, except maybe for the angel hair that forms when cleaning molten polymer off of a hot die or such. (Oh, and I can't forget about the stuff that conspiracy theorists believe is added to contrails.) Given that polymers have molecular weights of thousand, tens or hundreds of thousands and in some cases, millions of Daltons, they have no volatility at all and cannot evaporate.

But there is another way to get a polymer airborne, and that is to polymerize it in the air. "Science" had a report back in 2004 (open access copy) that showed polymers being built from various volatile organic components after exposure to UV light [*]. The degree of polymerization is not very high (the 9-mer seems to be as far as can be detected), so I would personally call them oligomers, but nonetheless, these chains still have molecular weights close to 1000 in some cases, too heavy to be launched by evaporation. (And given all the oxygen atoms in these hydrocarbons, there are a lot of dipoles along the chain, further increasing the molecular interactions and limiting volatility.)

[*] What spectral output did the light have? This is important, as some bulbs do a much better job matching the solar output that other bulbs do. But all reports in Science greatly lack in experimental details because of the space constraints.

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