1. Polymers
Polymers are giant molecules that are made up of many, many smaller molecules.
Building blocks for polymers are called monomers.
Examples: plastics, rubber etc.
Biopolymers: proteins, polysaccharides, nucleic acids

2. Polymers Biopolymers: Proteins Basic building blocks are amino acids
Amino acids linked together into proteins by amide groups
Peptide bonds formed by condensation reactions between two
amino acids.
e.g. Alanine + Glycine:
Gly
Ala
Gly-Ala

3. Polymers
Biopolymers:

4. Polymers
Amino acids:

5. Polymers Polysaccharides (Carbohydrates)
Monosaccharides linked together by ether-bridges
Representative segment of cellulose: a tough fibre.

6. Polymers Nucleic acids Composed of: H3PO4 molecule Organic base
5-C sugar

7. Polymers
In order to get a polymer formed we need a bifunctional molecule.

8. Polymers Addition Polymerization
Example: ethylene H2C=CH2, can polymerize by opening the C–C  bond to form C–C  bonds with adjacent ethylene molecules (with the help of radicals).
The result: polyethylene.
This is called addition polymerization because ethylene molecules are added to each other.

9. Polymers Step 1 Initiation: generation of radicals from catalyst
Step 2 radical adds to ethylene and polymerisation starts

10. Polymers

11. Polymers

12. Polymers
This is the repeat unit

13. Polymers

14. Polymers
repeat unit

15. Polymers Condensation Polymerization
Condensation Polymerization: molecules are joined by the elimination of a small molecule (e.g. water):
Example of condensation polymerization: formation of nylon.

16. Polymers

17. Polymers
Another example of a condensation polymerisation is the formation of nylon 6.
Used for clothing and mountaineering ropes amongst others

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20. Polymers

21. Polymers

22. Polymers Types of Polymers Plastic
Materials that can be formed into shapes by application of heat and pressure.
Thermoplastics:
Hard at room temp.
Become soft + viscous when heated.  can be
shaped more than once.
Little or no cross-linking  individual chains can slip
past each other.
E.g.’s include polyethylene, nylon, polystyrene….

23. Polymers Thermosetting resins:
Become highly cross-linked when heated.  solidify
into a hard, insoluble mass.
Can only be shaped once, polymerisation irreversible.
Can withstand high temperatures.
For example, Bakelite; used for adhesives, moulded
parts and coatings:
Phenol
formaldehyde

24. Polymers
Elastomers:
Have the ability to stretch out & spring back to their
original shapes.
Have a modest amount of cross-linking.
Polymer chains have irregular shapes.
Most common example is natural rubber

25. Polymers Structure and Physical Properties of Polymers
Polymer chains tend to be flexible and easily entangled or folded due to free rotation around the C–C single bonds.
Some regions of the polymer, may however, display a more ordered arrangement of chains than other regions:

26. Polymers Structure and Physical Properties of Polymers
The degree of crystallinity is a measure of the extent of such ordering.
More ordering in a polymer = denser, harder, less soluble polymers that are more resistant to heat.
e.g.
Properties of PE as a Function of Crystallinity.

27. Polymers Structure and Physical Properties of Polymers
Stretching or extruding a polymer can increase crystallinity.
Degree of crystallinity is also determined by average molecular mass:
Low density polyethylene (LDPE) has an average molecular mass of 104 amu (used in plastic wrap);
High density polyethylene (HDPE) has an average molecular mass of 106 amu (used in milk cartons).

28. Polymers Structure and Physical Properties of Polymers LDPE:
Obtained by polymerization of ethylene at high pressure
and high temperature.
Polymer chains have irregular branches and cannot pack
together in an ordered way.
Result: LDPE is an open polymer of low density and little
mechanical strength.

29. Polymers Structure and Physical Properties of Polymers HDPE:
Polythene can also be prepared catalytically at lower
pressures and temperatures.
Result: regular non-branched chain polymer which is highly
ordered or crystalline.
HDPE is tough and strong and the ordered structure means
that it has higher density.

30. Polymers Structure and Physical Properties of Polymers
Polyethylene is a very versatile material & it’s properties can be “fine tuned” by varying:

31. Polymers Cross-Linking Polymers
Bonds formed between polymer chains make the polymer stiffer.
Natural rubber is too soft and chemically reactive to make a useful material.
By vulcanizing the rubber (cross-linking the polymer chains) useful materials are made.
Rubber is usually cross-linked with sulfur.
Cross-linked rubber is stiffer, more elastic and less susceptible to chemical reaction.

32. Polymers
Cross-Linking Polymers