Some Polymer Basics

MORE About the Basics of Polymers

First, it's "Polymer Rules," not "Polymers Rule," although that's true also. Why do polymers rule? Well, think about the natural polymer DNA, the genetic code molecule that lists everything about any living organism. Those long strands of "triplets" tell how to put together an organism and how to make it work. The long and short of is, long DNA chains make things live. A collection of small molecules can't do that- there's no organization, no relationship information. It's not just that you have to have A, B and C in the mix, but you also have to have A connected to B which is connected to C. That connection sequence adds even more information that nature uses to make creatures and make them work right.

"Polymers Rule" for other reasons also. Polymers can have properties that small molecules never can. Take the synthetic polymer, ultra-high density polyethylene, for instance. Make it into a fiber, weave it into cloth and use it to make composite bullet resistant vests, and you save lives. Try to do that with a small molecule analog, candle wax. Yeah, wouldn't work the same, would it?

So that means there are fundamental differences between macromolecules and small molecules. Those differences go all the way from the molecular level to the nanoscopic and microscopic. In turn, these all impact the macroscopic level that we see and feel. We touched on some of these in the "Polymer Basics" page, but now it's time to dive in deeper.

So let's talk more about why polymers aren't as simple as small molecules starting at the molecular level. "It's complicated" just gets us started. It certainly is, but we have to look carefully at WHY it's complicated. What is it about polymers that are consequences of their huge size? And remember, we're talking mainly about how long the chains are, not how thick in cross sectional area. In truth, polymer molecules are about the same diameter as small molecules; it's just that they're so very, very long.
The first three rules are the same as from the introduction page. They're listed in the menu on the left, but we won't talk about them here much except when the lead to more intricate consequences, the "complicated" part.

Get in Line!

But usually we like to be more picky than that. 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.

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