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2ND YR- CSA- E lecs > Introduction to polymers > Flashcards

Introduction to polymers Flashcards

1
Q

How are polymers used in dentistry

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

What is the smallest unit n a polymer called/

A

A monomer

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3
Q

What is it called when 2 monomers rejoined together?

A

Dimer

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4
Q

What is a string of monomers joint together called?

A

A polymer

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5
Q

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

A

A macro molecule

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6
Q

What is a co polymer?

A

A polymer made up of more than one monomer species

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7
Q

Name the 3 different types of polymers?

A
  1. Block
  2. Graft
  3. Random
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8
Q

What is cross lining in relation to polymers?

A

Branching that occurs in a 3D psace network

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9
Q

Polymers that are linear or branched tend to be what?

A

Thermoplastic

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10
Q

What does it mean when a polymer is thermoplastic?

A

They can melt and be remodelled by heat

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11
Q

Give an example of thermoplastics we use in dentistry

A

Waxes

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12
Q

Crosslinked polymers are T……….

A

Thermosets

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13
Q

What dos it mean when a polymer is thermoset

A

They do not melt on heating

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14
Q

Give an example of thermoset polymers we use in dentistry

A

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

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15
Q

What is polymerisation?

A

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

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16
Q

What are eh 2 main subcategories of polymerisation

A
  1. Condensation polymerisation

2. Addition polymerisation

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17
Q

What is condensation polymerisation?

A

Where monomers react forming a polymer chain and a small brpoduct

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18
Q

What isi addition polymerisation?

A

Where monomers react simply forming a polymer and NO by product

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19
Q

How is condensation polymerisation said to occur?

A

Via step growth

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20
Q

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

A

Water

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21
Q

Give an example of a material produced via condensation polymerisation

A

Nylon

22
Q

How does addition polymerisation occur?

A

Via a chain reaction

23
Q

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

A
  1. Activation
  2. Initiation
  3. Propagation
  4. Termination
24
Q

How is the activation stage of a polymerisation reaction achieved?

A

Via some external energy

25
Q

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

A

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.

26
Q

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

A

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

27
Q

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

A

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

28
Q

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

A

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

29
Q

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

A

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.
30
Q

Name the 2 ways free radicals can be terminate

A
  1. Combination

2. Disproportionation.

31
Q

How are free radicals terminated in a combination reaction?

A

When 2 free radicals join together

32
Q

How are free radicals terminated in a Disproportionation reaction?

A

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

33
Q

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

A

Exothermic

34
Q

Are addition reactions described as eco or endothermic?

A

Exothermic

35
Q

What can polymerisation reactions result in?

A

Reduction in volume (shrinkage)

36
Q

Give an example of a polymerisation reaction that leads to shrinkage

A

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

37
Q

How can shrinkage be avoided in a polymerisation reaction?

A

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

38
Q

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

A

Glass particles can be used

Previously polymerised polymers can b used

39
Q

What gives the molecular mass of a polymer chain?

A

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

40
Q

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

A

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

41
Q

Why is the molecular mass important?

A

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

42
Q

Is glass an inorganic or organic polymer?

A

Inorganic

43
Q

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

A

It is highly ordered compact structure which is stronger

44
Q

What does it mean when a material is described as amorphous

A

It is a random loose network which is tough

45
Q

What is the Tg?

A

The glass transition temperature

46
Q

What does the Tg show?

A

The glass transition temperature, Tg,

It is the temperature region where the polymer transitions from a hard, glassy material to a soft, rubbery material.

47
Q

What increases the Tg?

A

Longer chains raise the Tg

Increasing cross links raises the TG

48
Q

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

A

said to be glassy

49
Q

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

A

Said to be rubbery

50
Q

What decreases the Tg?

A

Plasticisers

51
Q

What do plasticisers do?

A

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

2ND YR- CSA- E lecs (14 decks)

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