Polymers


 * // Polymers //** //////////////////////////////////////////////////////////////////////////////////////// The polymer page by : AnnMarie and Nathan

A polymer is a long chain of repeating units. These repeating units are called monomers. Monomers can vary from a simple two carbon chain to something large and more “complicated”.
 * What is a Polymer? **

Monomer unit, this monomer is called ethylene. Polymer from above monomer resembles the following: Note the repeating monomer units.

The polymer above has 6 monomers of ethylene. The double bond is no longer present as it was broken to form the adjacent bonds to another monomer. This type of polymer is called an **//addition polymer.//**


 * Changing the Properties of Polymers: **

The physical and chemical properties of polymers can be changed by crosslinking, crystallization, and stiffening. Each of these is a bit of a different concept and is discussed in detail below:

Cross linking is inserting a link that is permanent between two parallel polymer chains. This prevents sliding of the parallel polymers over each other and therefore causing the polymer to become more rigid and decrease its ability to flow.
 * Cross-linking: **



Polymer chains (no cross-linking) .......................................Polymer chains (cross-linking)

Stiffening is a bit different than cross-linking as there is no molecule or atom that is actually bonded to both polymers. Stiffening involves adding large molecules to the polymer chain therefore making it difficult for the polymer chains to slide past each other. Addition of large molecules creates a //steric hindrance//. This is a bulky molecule that when added to both polymers “gets in the way” preventing the polymers to slide past each other. This causes the polymer to become stronger and decreases its ability to flow.
 * Stiffening: **



Polymer chains (no steric hinderance) ..................................Polymer chains (with steric hinderance)

This is done by taking the polymers and lining up the chains very closely. This creates tighter packing which prevents as much sliding of the polymers due to the fact they are packed tightly.
 * Crystallization: **



Polymer (non-crystallized) ................................................Polymer (crystallized)

** Some classes of polymers: Biological Polymers **** and Plastics  ** ** Click on one of the above classes to go to that page for more information. **