1. POLYMERS

2. What is a polymer?
Polymers are large molecules made up small repeating units.
The repeating units in a polymer are called monomers.
Monomers are linked together in a polymerization reaction.
Polymers are widely abundant and may be natural or synthetic.
Some examples of polymers are rubber, polyvinyl chloride (PVC), polyethylene, Teflon, Kevlar, carbohydrates, proteins

3. Addition Polymers
Addition polymers result from addition reactions of monomers containing carbon-carbon double bonds.
Some examples of addition polymers include polyethene, polypropene, polyvinyl chloride, polystyrene and Teflon

4. Stages in an Addition Polymerization Reaction
There are 3 stages in an addition polymerization reaction.
Initiation  an initiating molecule (such as a peroxide) with an unpaired electron forms a bond with one of the C’s in the double bond.
Propagation  the “growing” phase.
Termination  the unpaired electron ends combine forming a covalent bond ending the reaction.

5. Condensation Polymers
Condensation polymers are formed when monomers are linked together through condensation reactions (removal of water).
Examples of condensation polymers include polyester, proteins, carbohydrates and Kevlar

6. Types of condensation polymer linkages
Ester linkages (you have seen these in esterification reactions)
(a reaction between a carboxylic group and an alcohol (hydroxyl group))
- polymers with ester linkages have the general name of polyesters
Eg. Polyethylene, PET

7. Types of condensation polymer linkages
b) Amide linkages
Occur between an amine group and a carboxyl group
Called polyamides in general
Examples include Kevlar, Dacron

8. The Effect of Substituted Groups on Polymer Properties
The reactivity, solubility and strength of a polymer is due to the groups that are attached to the polymer chain.
Teflon (polytetrafluoroethane) for example is very unreactive because the C-F is very strong.
Monomers that contain 2 double bonds are able to add to other molecules in two ways which means a single monomer can be incorporated into 2 different polymer chains causing bridges between the polymer chains.

9. These bridges are called “crosslinks” and may be formed intermittently along the polymer chains.
These links between polymer chains are covalent bonds and are much stronger than the van Der Waals forces that would otherwise hold the chains together.
As the degree of crosslinking increases so does the strength of the molecule.
A high degree of crosslinking will also make the polymers heat resistant and more elastic.
Crosslinks may also be formed with inorganic crosslinking agents such as sulfur.

10. Homework
Page 121 #53-#62