27 May 2012

Polymers and Monomers

Choose one:
Part 1: A Look at Polymers
Part 2: A Look at Monomers

Part 1: A Look at Polymers

Look at the term: polymer
Poly- means "many."

Study these examples for a moment:
polytechnic  many technical subjects
polygon  many-sided figure
polyunsaturated  many double bonds
So what does polymer mean?
Polymer means many monomers. Sometimes polymers are also known as macromolecules or large-sized molecules. Usually, polymers are organic (but not necessarily).
A monomer is a molecule that is able to bond in long chains.
Here is a monomer:     

Here is a polymer:     

A polymer can be made up of thousands of monomer.
This linking up of monomers is called polymerization.
It is the long chains that give polymers their unique properties. Consider ethane, CH3-CH3, which is a gas molecule at room temperature. Because of their small size, ethane molecules are very mobile and can run almost anywhere they want without interacting with other molecules. Now, if we double the chain length or the total number of carbons to four, we get butane, CH3-CH2-CH2-CH3, which is a liquid fuel. In liquids, atoms or molecules can no longer act as independent units. Because of their larger size, butane molecules are less mobile than ethane molecules. Their lowered mobility allows them to run into or interact with one another more frequently. When the chain length increases 6 fold, as in paraffin, CH3(CH2CH2)10CH3, we get a waxy substance. In this case, the solid-like propertyof paraffin is a reflection of the entanglement of its long molecules when they move. If we keep increasing the number of repeating carbon units to, say, 2000, i.e., CH3(CH2CH2)2000CH3, we have a polyethylene polymer, which is a very strong, brittle solid. The polymer molecules have become so long and so entangled that their movement becomes almost completely restricted. At this point, they appear to be attached to other molecules, which act as "permanent" neighbors.

Ethane CH3-CH3 2 C atoms gas
Butane CH3-CH2-CH2-CH3 4 C atoms liquid
Paraffin CH3(CH2CH2)10CH3 22 C atoms wax
Polyethylene CH3(CH2CH2)2000CH3 4002 C atoms solid
Monomers link together by two basic methods:
addition polymerization and
condensation polymerization

Part 2: A Look at Monomers

To get a clear idea of the way polymers are formed, you need to look more closely at the monomer molecules! There are many monomer molecules. Here are some examples:

Each of these monomer molecules seems very different, but they do have some common features. Let's see if you can spot them.
Look again at the first four monomers:

What is the feature found in each of these monomers? Click on this feature.
Actually, these monomers have two distinctive features:
carbon-carbon double bonds and
side groups
The highlighted areas show the side groups on these monomer molecules. These groups give the polymer chain some of its properties.

The double bond, however, is the vital feature that allows these monomers to form the long polymer chains.
Now, let's look at those other four monomers. (Note: we have two different groups of monomers because we have two different polymerization reactions.) These four monomers contain what we call functional groups. You may already know that much of the chemistry of carbon compounds is based on certain groups of atoms that are called functional groups. Let's take a look at a few.
One example of this is the carboxylic acid group:

R means the "Rest" of the molecule.
Here are two example monomers that contain this functional group:

Two other functional groups you may see in polymerization reactions are the amine group, , and the alcohol group, . Below are examples of monomers containing these functional groups:

Notice that each of these monomers contains two functional groups. That is, they are difunctional. It is their difunctionality that allows them monomers to form long polymer chains.
As we move on to polimarization, remember what you read about monomers:
The first group of monomers had
carbon-carbon double bonds and
side groups
The second group of monomers had
functional groups and
two functional groups each (that is, they are difunctional)
Let's move on to polimarization.


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