1. Chapter 15
Polymers

2. Plastics They deform readily Usually a polymer plus an additive
Organic molecules
Three Dimensional
Monomer -> Polymer

3. Classes Thermoplastics Thermosets Elastomers Soften when heated
Remain rigid until they decompose
Elastomers
Deform, then regain their shape

4. How Does Polymerization Occur
Addition
Polyethylene
Condensation
Nylon

5. n H2 C = C H2 -> -CH2 CH2 CH2 CH2 CH2 CH2 -
Addition Polymer
n H2 C = C H2 -> -CH2 CH2 CH2 CH2 CH2 CH2 -
Polymer
Monomer
Condensation Polymer
R – COOH H2N-R’ -> H2O + R-CO – NH – R’
Monomer 1
Monomer 2
Copolymer

6. Length of the Chains Initiation Termination
A molecule comes along and breaks the double bond. That leaves a dangling electron, that needs to react.
The reactive end adds to other monomer molecules
Termination

7. Initiator
Disassociation of Hydrogen Peroxide
H2O > 2OH
OH + H2C=CH2 -> HOCH2CH2 .

8. Termination

9. Linear Polymers See the CD Bond Rotation
Molecules are always in motion
The amount of motion possible depends on the constituents attached to the chain
Its not just chemistry – its physical room!!

10. Elastomers Lightly Crosslinked
Unkink – which produces large elastic strain
Vulcanization
Open up double bonds
Attach sulfur
Crosslinks the chains

11. Elastomers
When you stretch a rubber band, you unkink the polymer, and you break van der Waal bonds – Do it!!
Check the temperature
Why did the temperature go up?
What happened to the temperature when you released the rubber band?

12. Network Polymers Linear polymers are long chains
If there is more than one attachment point, the chains branch
The result is a network – Lots of crosslinking
Usually formed by condensation
Bakelite is an example – Used in electrical fixtures
Epoxy Resins are network polymers

13. Properties Polymers can crystalize, but its hard (Why?)
More often they are amorphous, and so they have properties more like glass
Glass transition temperature
Modulus of Elasticity changes at the glass transition temperature, as do other properties
Often room temperature is above the glass transition temperature

14. Properties Strain Hardening “Spagetti” Experiment What is crazing?
When the polymers align they move closer together, leaving voids
The material eventually becomes a series of fibrils
Finally break

15. Stress Relaxation All materials “creep” at high temperature
For most polymers RT is a high temperature
Molecules slide past each other, given enough time, when a moderate load is applied
If the load is applied quickly, the molecules break
You can watch this happen in Silly Putty

16. Branching Isotactic Syndiotactic Atactic Try the quiz All on one side
Greatest Regularity - Stronger
Syndiotactic
Alternating
Atactic
Random
Try the quiz

17. Friday Experiments Shyla – Strain hardening of “Glad” Wrap
Dan – Weibull modulus
Holly – Silly Putty

18. Monday Review Final is Monday, May 7th
Your final homework assignment is to complete the “Sample Final”, which you’ll find on line.
Bring it with you to the final.