H-B Woodlawn Biology
POLYMER BASICS
(source: University
of Southern Mississippi Department
of Polymer Science)
This is an introductory page concerning polymers, which are large
macromolecules with molecular weights in the range of several thousand
or more.
Most of the time when we talk of polymers we're talking about molecules
with molecular weights of hundreds of thousands, or even millions. We're
also usually talking about linear polymers. A linear polymer is
a polymer molecule in which the atoms are more or less arranged in a long
chain. This chain is called the
backbone. Normally, some of these
atoms in the chain will have small chains of atoms attached to them. These
small chains are called pendant groups. The chains of pendant groups
are much smaller than the backbone chain. Pendant chains normally have
just a few atoms, but the backbone chain usually has hundreds of thousands
of atoms.
Polymers Are Like TV: Both Have Lots and Lots of
Repeats
Normally, too, when we talk of polymers, we're not just talking about
huge molecules whose atoms are arranged in chains. We like to think that
the atoms that make up the backbone of a polymer chain come in a regular
order, and this order repeats itself all along the length of the polymer
chain. For example, in
polypropylene,
the backbone chain is made up of just two carbon atoms repeated over and
over again. One carbon atom has two hydrogen atoms attached to it, and
the other has one hydrogen atom and one pendant methyl group.
This unit of a carbon atom with two hydrogen atoms followed by a
carbon atom with a hydrogen atom and a methyl group repeats itself over
and over again along the backbone chain. This little recurring structure
is called the repeat structure or the repeat unit.
To make things simple, we usually only draw one unit of the repeat
structure, like this:
The repeat unit is put inside brackets, and the subscript n
just stands for the number of repeat units in the polymer chain.
Breaking the Line
Polymers can come in other structures, though. To find out, take a look
at the nonlinear polymer
page.
The Consequences of Being Big
Let's get back to those simple linear polymers, now. These giant chain-like
molecules, because they are so big and because of their shape, act in ways
which small molecules don't. There are three reasons for this. To find
out what they are, take a look at the page we call Three
Things That Make Polymers Different.
Some Assembly Required
Polymers don't start out big. They start as little tiny molecules called
monomers.
To make a polymer, a whole mess of monomers are strung together in a line
to form a long polymer chain. For example, styrene monomers are joined
together to make polystyrene:
For more on building polymers from monomers, go here.