Wednesday, April 17, 2013

Polymers from Elemental Sulfur

I written a fair bit in the past about my interest in thiol-ene polymers, but that is as far as my love affair with sulfur-based polymers has gone. Until now. A new paper in Nature Chemistry (pay-per-view) shows the copolymerization of elemental sulfur with a vinyl monomer. While this has been done in the past, this is the first time that it was done solvent-free - a divinyl monomer was dissolved in molten sulfur and copolymerized.

Sulfur is a large waste product of petroleum refining. While it only is present in a very small amount - just a few percent or less - its presence is a huge headache for refiners and the public in general. For the refiners, the sulfur quickly poisons the various catalysts used in the refinery. And since 90% of petroleum products are intended to go straight in some form of combustion reaction (both heating and transportation), sulfur in those fuels is oxidized to SOx, which eventually ends up as sulfuric acid in the atmosphere. And so the sulfur is quickly removed for the good of one and all.

An obvious way to reduce the amount of sulfur removed is to simply buy crude oil with less sulfur in it. Petroleum with less than 0.5% sulfur is referred to as "sweet" crude and commands a higher price because of the greater demand. But even given these options, refineries still end up producing way to much sulfur and there is only so much demand for sulfuric acid. So being able to use a cheap feedstock like sulfur is a good option even if the comonomer (diisopropenyl benzene) is a little bit offbeat. The fact that this polymer is crosslinked by the organic compound and not the sulfur compound is the inverse of a normal vulcanized rubber and so the authors call this "inverse vulcanization". This is neat concept that bears further exploration.

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