Introduction to polymers

Question 1

How are polymers used in dentistry

Answer 1

1. Alginate impression materials and poly methyl methacrylate, acrylic denture base resin.
2. silicon impression materials revolutionise fixed prosthetic dentistry.

Question 2

What is the smallest unit n a polymer called/

Answer 2

A monomer

Question 3

What is it called when 2 monomers rejoined together?

Answer 3

Dimer

Question 4

What is a string of monomers joint together called?

Answer 4

A polymer

Question 5

What large molecules made up of tens of thousands of monomers called?

Answer 5

A macro molecule

Question 6

What is a co polymer?

Answer 6

A polymer made up of more than one monomer species

Question 7

Name the 3 different types of polymers?

Answer 7

1. Block
2. Graft
3. Random

Question 8

What is cross lining in relation to polymers?

Answer 8

Branching that occurs in a 3D psace network

Question 9

Polymers that are linear or branched tend to be what?

Answer 9

Thermoplastic

Question 10

What does it mean when a polymer is thermoplastic?

Answer 10

They can melt and be remodelled by heat

Question 11

Give an example of thermoplastics we use in dentistry

Answer 11

Waxes

Question 12

Crosslinked polymers are T……….

Answer 12

Thermosets

Question 13

What dos it mean when a polymer is thermoset

Answer 13

They do not melt on heating

Question 14

Give an example of thermoset polymers we use in dentistry

Answer 14

the denature base resin Poly methyl methacrylate (PMMA or acrylic) is a thermoset.

Question 15

What is polymerisation?

Answer 15

The act of reacting monomers or co-monomers to form a polymer

Question 16

What are eh 2 main subcategories of polymerisation

Answer 16

1. Condensation polymerisation

2. Addition polymerisation

Question 17

What is condensation polymerisation?

Answer 17

Where monomers react forming a polymer chain and a small brpoduct

Question 18

What isi addition polymerisation?

Answer 18

Where monomers react simply forming a polymer and NO by product

Question 19

How is condensation polymerisation said to occur?

Answer 19

Via step growth

Question 20

Name a common condensate that may be produced in a polymerisation reaction?

Answer 20

Water

Question 21

Give an example of a material produced via condensation polymerisation

Answer 21

Nylon

Question 22

How does addition polymerisation occur?

Answer 22

Via a chain reaction

Question 23

What are the 4 distinct stages of an addition polymerisation reaction?

Answer 23

1. Activation
2. Initiation
3. Propagation
4. Termination

Question 24

How is the activation stage of a polymerisation reaction achieved?

Answer 24

Via some external energy

Question 25

What happens in the activation stage of an addition polymerisation reaction ?

Answer 25

A chemical known as the initiator is added by the manufacturer to the monomer. The act of activation splits the initiator molecule releasing two new ends that were covalently bonded these are very reactive free radicals.

Question 26

What is the initiator chemical used in an addition polymerisation reaction sensitive to?

Answer 26

This chemical is sensitive to either heat, light or an additional chemical

Question 27

What happens in the initation stage of an addition polymerisation reaction ?

Answer 27

The free radicals now home in on the weak points in the monomer

Question 28

What happens in the propagation stage of an addition polymerisation reaction ?

Answer 28

The free radical then reacts with another monomer and the free radical gets passed on.

Question 29

What happens in the termination stage of an addition polymerisation reaction ?

Answer 29

the free radical either: 1. meet another free radical coming the other way this is called combination, 2. The free radicals could be terminated by pinching a hydrogen from the end of an other chain this is called called disproportionation.

Question 30

Name the 2 ways free radicals can be terminate

Answer 30

1. Combination | 2. Disproportionation.

Question 31

How are free radicals terminated in a combination reaction?

Answer 31

When 2 free radicals join together

Question 32

How are free radicals terminated in a Disproportionation reaction?

Answer 32

Who a free radical "pinches" a hydrogen from the end of another chain

Question 33

What type of reaction is the braking of double bonds described as?

Answer 33

Exothermic

Question 34

Are addition reactions described as eco or endothermic?

Answer 34

Exothermic

Question 35

What can polymerisation reactions result in?

Answer 35

Reduction in volume (shrinkage)

Question 36

Give an example of a polymerisation reaction that leads to shrinkage

Answer 36

The conversion of methyl methacrylate into poly methyl methacrylate can result in a 30 % reduction in volume.

Question 37

How can shrinkage be avoided in a polymerisation reaction?

Answer 37

Simples ways to incorporate filler particles of a material that does not change volume

Question 38

Give an example of filler particles used to avoid shrinkage in polymerisation reaction

Answer 38

Glass particles can be used | Previously polymerised polymers can b used

Question 39

What gives the molecular mass of a polymer chain?

Answer 39

The product of the molecular mass of the monomer and the degree of polymerisation (n) gives the molecular mass for a particular chain.

Question 40

As polymers have varying chain lengths how can we find the molecular mass using a graph?

Answer 40

We take the number average molecular mass his calculates what length chain the average (mean) monomer resides in.

Question 41

Why is the molecular mass important?

Answer 41

As it leads to differences in the properties of chemical identical materials

Question 42

Is glass an inorganic or organic polymer?

Answer 42

Inorganic

Question 43

What does it mean when a material is described as crystalline?

Answer 43

It is highly ordered compact structure which is stronger

Question 44

What does it mean when a material is described as amorphous

Answer 44

It is a random loose network which is tough

Question 45

What is the Tg?

Answer 45

The glass transition temperature

Question 46

What does the Tg show?

Answer 46

The glass transition temperature, Tg, | It is the temperature region where the polymer transitions from a hard, glassy material to a soft, rubbery material.

Question 47

What increases the Tg?

Answer 47

Longer chains raise the Tg | Increasing cross links raises the TG

Question 48

Polymers below the glass transition temp (Tg) are described as what?

Answer 48

said to be glassy

Question 49

Polymers above the glass transition temp (Tg) are described as what?

Answer 49

Said to be rubbery

Question 50

What decreases the Tg?

Answer 50

Plasticisers

Question 51

What do plasticisers do?

Answer 51

They lower the Tg by allowing the polymer chain to move more freely basically working as a lubricant