Polymer Materials

Question 1

What is the basic polymer structure?

Answer 1

Consists of long chain molecules with a backbone of carbon atoms covalently bonded together

Question 2

What is a Mer unit?

Answer 2

Basic repeat unit a chain is formed of

Question 3

Types of polymerisation

Answer 3

Addition polymerisation

Condensation polymerisation

Question 4

What by-products does condensation polymerisation produce?

Answer 4

Water or acetic acid

Question 5

What are the three main types of polymer?

Answer 5

Thermoplastics
Thermosets
Elastomers

Question 6

What are the properties of thermoplastics

Answer 6

Only secondary bonds
Solids at room T
Recyclable
Injection moulded
Amorphous or semi-crystalline

Question 7

What are the properties of thermosets

Answer 7

Many covalent bonds (cross-links)
High strength, stiffness and hardness
Cannot be recycled
Good chemical resistance
Higher operating T than thermoplastics

Question 8

What are the properties of elastomers

Answer 8

Few covalent cross-links

Chains uncoil under stress reducing entropy

Question 9

What is the degree of polymerisation?

Answer 9

The average number of mer units in the chain

Question 10

What are copolymers?

Answer 10

chains with two different mer units that can be regularly arranged, randomly arranged or formed into blocks. Chains of different mer units can also be attached – grafted on

Question 11

How does cooling determine the level of crystallinity

Answer 11

Fast cooling - less crystalline

Slow cooling - more crystalline

Question 12

What are spherulites?

Answer 12

The lamellae start from a central nucleation site and grow into spherical arrangements called spherulites

Question 13

How do side groups affect crystallinity

Answer 13

Atactic molecules do not normally form crystals

Large side groups can also reduce chain mobility making crystal formation difficult.

Question 14

What are Viscoelastic materials?

Answer 14

Exhibit elastic behaviour when loaded over a short time scale, but will flow, i.e. appear viscous when loaded over a longer time scale.

Question 15

What is meant by Deflection temperature?

Answer 15

The temperature at which a given deformation of a beam occurs for a standard load -indicates the likelihood of creep.

Question 16

Name some properties of Silicones

Answer 16

Made up of Si-O rather than C
Generally thermosets
Form at room T
Flexible
Resistant to weathering, oils

Question 17

What are the properties of thermoplastic elastomers?

Answer 17

Rely on glassy regions where the chains pack together well to form lots of secondary bonding. Act like cross links to stop permanent displacement of chains relative to one another.

Question 18

What are some examples of fillers?

Answer 18

can be sand, glass, clay.

Question 19

What do fillers improve?

Answer 19

tensile and compressive strength, abrasion resistance, toughness and dimensional stability

Question 20

What a plasticisers?

Answer 20

small molecules added to the polymer that obstruct secondary bonding. Reduce hardness and stiffness

Question 21

Name four other polymer additives

Answer 21

Stabilisers
Flame retardants
Pigments
Anti-static agents