Let's learn what different types of polymers are there and what are special about them in A-Level Chemistry!
Thermoplastics
- Contain polymers with no cross-links between the chains
- Intermolecular bonds between the chains are much and so the bond can be broken by warming
- Cross-links allow the chains to move
Thermosetting
- Polymers have extensive cross-linking
- Intermolecular bonds are stronger and not broken by heating
- Chains cannot move
How Polymers are affected by Temperature
Crystalline Regions
Arranged order or polymer chains
Amorphous Regions
Random order or polymer chains
At room temperature, most polymers have some crystalline regions and some amorphous regions.
Cooling the polymer gives a higher percentage of crystalline regions. Heating the polymer gives a higher percentage of amorphous regions.
Tg = glass transition temperature
when the polymer is warmer than this temperature, it becomes flexible
Tm = melting temperature
when the polymer is warmer than this is becomes more liquid
Questions
1. The physical properties of a polymer depend on temperature. Describe the properties of a polymer at temperatures above it’s Tm. Describe and explain the properties of a polymer at temperatures below it’s Tg.
• Above Tm: polymer melts, becomes liquid
• Below Tg: polymer becomes brittle because chains cannot move over each other so break when force is applied
2. Give the meaning of the term crystallinity when it is used to discuss the properties of polymers
• How polymer chains/ molecules/ sections are packed together in an orderly way
• How polymer chains are aligned/lined up
3. PPA has more crystalline areas than nylon-6. This gives PPA a greater Tm than nylon-6. Explain this greater Tm in terms of the intermolecular bonding involved.
• PPA chains are closer together
• Intermolecular bonds in PPA will be stronger
• More hydrogen bonds in PPA
• More intermolecular bonds in PPA
• More energy/heat will be required to break the intermolecular bonds or melt the polymer or allow chains to move over each other
3. Explain how a Tg of 9Oc indicates that at room temperature the polymer PMA and the polymer PMMA with a Tg of 114Oc is brittle
• Tg of PMMA is above room temperature so will be brittle / not enough energy to break intermolecular bonds / chains cannot move over each other
• Tg of PMA is below room temperature so will be flexible / rubbery / enough energy to break intermolecular bonds / chains can move over each other
4. Give a reason why an extra methyl group alters the flexibility of a polymer
• Chains can slide over each other more easily
Drafted by Eunice (Chemistry)