So what's so great about polyketones? Let's find out by taking a look at
them. A polyketone is of course a polymer with a ketone group in
the backbone chain. The polyketones we're going to talk about on this
page are based on the picture you see at the top of the page, where
R' is an ethylene linkage, -CH2CH2-. Shell
has just put this family of polymers on the market and sells them under
the name Carilon. This is not to be confused with a carillon,
which is a musical instrument with differently pitched bells, which
controlled with a piano-like keyboard. Let's see what one of these polymers looks like, next to a chain of good
ol' polyethylene for comparison:
It's not much different. The only difference is that the polyketone has
those carbonyl groups in it. But those carbonyls do a lot. You see,
carbonyl groups are very polar.
This is because oxygen is electronegative
and draws electrons away from the carbon atom. So oxygen has a slight
negative charge and the carbon has a slight positive charge.
These polar carbonyl groups are attracted to each other, and very strongly
at that. This attraction is so strong that while polyethylene melts at a
mere 140oC, the polyketone doesn't melt until 255 oC!
This is all very nice, but really, now, what's the big deal? There are
lots of high performance plastics out there. There are poly(ether sulfones), poly(phenylene sulfide), polyimides... We've seen high performance
before. What makes polyketones so special?
This is what makes polyketones so special. To make polyketones, you take
ethylene gas and carbon monoxide, and react them with a palladium(II)
Ethylene is dirt cheap; it's the monomer for polyethylene. Carbon monoxide is dirt cheap, too.
You make carbon monoxide every time you burn wood, or a candle, or just
about anything containing carbon. The reaction is also easy to carry out.
Most high performance polymers are difficult to make, because the
chemistry has to be just right for the reactions to work.
Cheap monomers, and easy chemistry make polyketones rather cheap, a whole
lot cheaper than other high performance plastics.
In time the price may come down to less than a dollar per pound! This is why we think a lot of
stuff is going to be made out of
polyketones in the future.
Here's some models of the monomers if you want to play with them. Ethylene is on the left and carbon monoxide is on the right.
Every now and then you get an extra methyl group attached to one of the
ethylene units. These methyl groups get in the way when the polymer
chains try to pack into crystals. They can still pack, but not as well as
before. The bad part is that the melting temperature drops to about 220
oC, because the crystals aren't as strong. But the good part
is that the polymer is now a lot tougher and less brittle.
This polyketone made with ethylene, carbon monoxide, and a little bit of
propylene is the Carilon that you can buy.
Keep watching this page. As soon as we find out what people are making
out of polyketones we'll post something here about it!
Polymer Science Learning Center
Department of Polymer Science
The University of Southern Mississippi