Polymers

Question 1

What is a polymer?

Answer 1

Materials
consisting of long molecular chains made up of many
repeating sections, generally long hydrocarbon chains

Question 2

Describe Covalent bonding

Answer 2

very strong intermolecular bonds where atoms share electrons between them to fill there valancies

Question 3

Describe Van der Waals Bonding

Answer 3

molecules can distort each others electron clouds causing net positive and negative zones which cause a weak connection between tthe molecules

Question 4

What is a thermoplasic ?

Answer 4

single unbranched chains of polymer which connect with only van der waals bonds allowing them to be melted and reformed easily

Question 5

What are the three forms thermoplasics can take?

Answer 5

Amorphous solids
Crystalline solids
Glassy solids

Question 6

Describe an amorphous thermoplasics

Answer 6

chaotic mess of chains which interact randomly with no overall structure
Amorphous
Low stiffness
Flexible

Question 7

Describe a Glassy solid thermoplastic

Answer 7

at lower temperatures amorphous polymers cannot easily slide over each other
results in a hard brittle material

Question 8

What is a Glass transition temperature?

Answer 8

the temperature below which amorphous solids become glassy solids due to restricted chain movement

Question 9

Describe a crystalline thermoplastic

Answer 9

long chains form a regular ordered pattern with chains lying paralell to each other

Question 10

what is the degree of crystalinity?

Answer 10

polymers contain both crystalline and amorphous regions, degree of crystallinity shows the amound of crystal polymer present

Question 11

How does the degree of crystalinity affect a material?

Answer 11

Increased crystallinity
* Increases density
* Increases strength
* Increases melting point

Question 12

What is a thermoset polymer?

Answer 12

long chained polymers are connected together in a chemical reaction creating cross links between them

Question 13

how does cross linking affect the properties of thermosets

Answer 13

the polymer cannot be melted and reformed
only amorphous structures can be created
very strong materials as chains are covalently bonded together

Question 14

What is a two part thermoset?

Answer 14

thermosets which form from the mixing and subsiquent reaction of two chemicals

Question 15

What is a heat activated thermoset?

Answer 15

A single part thermoset polymer which cures under high temperatures creating cross links with its neighbours

Question 16

What is a radiation activated thermoset?

Answer 16

A single part thermoset polymer which cures under exposure to radiation, usually UV, creating cross links with its neighbours

Question 17

what is an elastomer?

Answer 17

long chained amorphous polymers with a small amount of cross linking

Question 18

how does the bonding of an elastomer give it its elastic properties?

Answer 18

long chains with small cross links transferes forces along the length of the material. the cross links prevent plastic deformation so the bonds strech elastically