Polycarbonate gets its name from the carbonate groups in its backbone
chain. We call it polycarbonate of bisphenol A because it is made from
bisphenol A and phosgene. This starts out with the reaction of bisphenol
A with sodium hydroxide to get the sodium salt of bisphenol A.
The sodium salt of bisphenol A is then reacted with phosgene, a right
nasty compound which was a favorite chemical weapon in World War I, to
produce the polycarbonate.
What? You want the gritty details of the reaction? Then click here and you will not be disappointed.
Another polymer used for unbreakable windows is poly(methyl methacrylate).
So what is this wonderful new polycarbonate? It's very different from
polycarbonate of bisphenol A. We make it by starting with this monomer:
You can see that it has two allyl groups on the ends. These allyl groups
have carbon-carbon double bonds in them. This means they can polymerize
by free radical vinyl polymerization. Of
course, there are two allyl groups on each monomer. The two allyl groups
will become parts of different polymer chains. In this way, all the
chains will become tied together to form a crosslinked material that looks like this:
As you can see, the carbonate-containing groups (shown in blue) for the
crosslinks between the polymer chains (shown in red). This crosslinking
is makes the material very strong, so it won't break nearly as easily as
glass will. This is really important for kids' glasses! If only this
stuff had been invented when I was a kid!
There is a fundamental difference in the two types of polycarbonate
described here that I should point out. Polycarbonate of bisphenol A is a
thermoplastic. This means it can be molded
when it is hot. But the polycarbonate used in eyeglasses is a thermoset. Thermosets do not melt, and
they can't be remolded. They are used to make things that need to be
really strong and heat resistant.
Other polymers used as plastics include:
Other polymers used as thermosets
For more information, at other websites...
Polymer Science Learning Center
Department of Polymer Science
The University of Southern Mississippi