Polycarbonate (From greenhouse gas to eyeglass lens, CO2 does it all!)
22nd June 2006
Even my peers make fun of me for this - it continually blows my mind that carbon dioxide is a part of a plastic. Logically, I know that there’s nothing special about a gas becoming incorporated into a nonvolatile chemical (ethylene, for example, is a gas and is incorporated into polyethylene, another plastic!). I think the idea has always rocked my world because CO2’s so ubiquitous and comes out of things like you, me, and fire. CO2, you see, can actually combine with a molecule of water to form carbonic acid:
This is the reason carbonated liquids have a bit of a bite to them; they’re actually acidic! This is a regular carboxylic acid for the most part, and it acts like one. It has an acid chloride mate in phosgene, famed insecticide, war gas, and plastic precursor.
Phosgene reacts with the oxygens in bisphenol A; they are deprotonated by the base present, causing them to become anions and thus more inclined to react with the extremely electrophilic phosgene carbon. Out of this, you get “polycarbonate,” which is just the polyester of bisphenol A and carbonic acid. You also get some salt from the NaOH and COCl2. This is just a common polycarbonate; the term is generally used to describe any polyester of carbonic acid.
Polycarbonate is amazing. Polycarbonate, superstar that it is, is one of a few plastics that is both optically clear and strong enough to make lenses, letting nearsighted children play happily without fear of breaking their glasses. Ever hear of bulletproof glass? It’d be a lot harder for P. Diddy and the Pope alike without polycarbonate. All this from what’s essentially an ester of hydrated carbon dioxide. Amazing!
June 22nd, 2006 at 9:34 pm
Not to nitpick but wouldn’t they more likely to use triphosgene in the case of polymer synthesis? It’s a lot more stable, less toxic and solid, or was the original synthesis done with phosgene?
June 22nd, 2006 at 9:40 pm
You are probably right, but I really don’t know my process chemistry, and I went with the easiest-to-understand route. Wikipedia says phosgene, but I’m not putting any bets on a Wiki entry. For the uninitiated, here is triphosgene :
It acts like three molecules of phosgene. The advantage is that it’s not a gas. Still a violent poison, but you’re less likely to breathe it in. There is also an analagous diphosgene (triphogene is a solid, diphosgene is a liquid, and phosgene is a gas).
June 28th, 2006 at 12:20 am
I’d personally like to see a new method created for putting carbon dioxide into a solid form (even if it’s chemically modified like this) - then we could take carbon dioxide from the atmosphere, chemically treat it into a solid form, and store it away in warehouses! No more greenhouse gases.
And if we wanted to kill two birds with one stone…find a way to filter mercury out of water….and store it as mercury carbonate!
I’m a genius!
June 29th, 2006 at 5:15 am
Will not the use of triphosgene lead to multiple links with Bisphenol giving rise to a “three-dimensional” network rather than a linear chain? Will such a crosslinked polymer be useful in applications where linear polymer fails - say heat resistance?