5.7 Polymer Properties by Design 2

Question 1

What do longer chains mean?

Answer 1

Stronger polymers.

Question 2

What needs to be reached before the strength increases?

Answer 2

A critical strength needs to be reached before the strength increases.

Question 3

What is tensile strength?

Answer 3

The measure of how much you have to pull on a sample of a polymer before it snaps.

Question 4

What two factors lead to an increase in tensile strength i or a polymer with increasing chain length?

Answer 4

1. Longer chains get tangled=difficult for chains to slide over each other=reducing flexibility.
2. Chains are longer=more points of contact with neighboring polymer molecules=more intermolecular bonds to hold the chains to one another=chains are attracted more strongly=difficult for the chain to slide over each other=polymer less flexible.

Question 5

How do you change the Tg (Glass transition state)?

Answer 5

1. Copolymerisation

2. Plasticers.

Question 6

How do you make the polymer more flexible.

Answer 6

Tg value must be lowered. PVC is 80 Tg therefore at room temperature very brittle.

Question 7

Co-polymersie

Answer 7

Add a molecule to the orginal polymer for example PVC and ethenyl ethanoate.

Question 8

What does co-polymerising do?

Answer 8

It introduces different side groups into the polymer chain. Therefore the chains pack together less well and the bonds between the chains are weaker. Polymer is more flexible because chains move over each other easier

Question 9

Plasticiser

Answer 9

Molecular lubricant that allows chains to slide around each other more easily.
Plasticiser molecules push PVC chains apart and help them slide. The polymer is flexible.

Question 10

Crystalline

Answer 10

Crystals have a regular shape externally because the ions are packed inside in a very ordered way.

Question 11

Which polymers are most likely to contain extensive crystalline regions.

Answer 11

Regular chain structures, such as isotactic poly(propene) without bulky side groups or extensive chain branching.

Question 12

What is important in determining the polymers properties?

Answer 12

The proportion of crystallinity in a polymer.

The more crystalline a polymer, the stronger and less flexible it becomes

Question 13

If a polymer is more crystalline why is it less flexible.

Answer 13

Polymer chains pack closely together, maximizing intermolecular bonds.
Chains slide over each other less easily and the polymer will be more rigid than polymers with large amporpbous regions.

Question 14

What happens if polymers are really amorphous?

Answer 14

They do not pack close together
The intermolecular bonds are very weak
Polymer chains slide over each other easily
Polymer is flexible

Question 15

What is cold drawing?

Answer 15

When a polymer is stretched (cold-drawn) a neck forms.

Question 16

What happens in the neck?

Answer 16

Polymer chains are liner up to form a more crystalline region.
Proportion of crystalline regions is increased, cold-drawing leads to a signigicnat increase in the polymers strength. Used to produce tough fibres.