Lecture 3

Question 1

Polymer materials consist of

Answer 1

long chain molecules usually with a back bone of carbon atoms

Question 2

What bonding do we see in polymers?

Answer 2

covalent

Question 3

Polymers can ……… that enables it to twist into a variety of positions

Answer 3

rotate around the axis of the C-C bond

Question 4

What changes the polymers chain structure and properties?

Answer 4

Side groups

Question 5

Mer unit is

Answer 5

the basic structure that the chain is formed from

Question 6

Condensation polymerisation usually

Answer 6

combines two different monomers into the chain

Question 7

Condensation polymerisation produces a small

Answer 7

molecule by-product

Question 8

Which polymer; only secondary bonds between the polymer chains%

Question 9

Which polymer; many cavalent bonds (cross-links) between the polymer chains%

Question 10

Which polymer; rubbery materials can be thermoset or thermoplastic versions%

Question 11

Thermoplastic polymers are

Answer 11

polymers that consist of many molecules that are linked to each other ONLY by secondary bonds and entanglement

Question 12

A stronger thermoplastic polymer means what for the glass transition temp?

Answer 12

higher glass transition temp

Question 13

The absence of primary bonds in thermoplastic polymers means that the chains can

Answer 13

slide past each other when loaded at a high temp

Question 14

By heating a thermoplastic polymer what does it turn into? What can we do with this?

Answer 14

Viscous liquid - which can be formed and moulded easily

Question 15

Differences in the depiction of an amorphous and semi-crystalline thermoplastic?

Answer 15

Amorphous - scribbled mess, intertwined and messy

Semi-crystalline - regular neat chains snaking around each other

Question 16

Through a polymerisation process, what can we not determine without controlling the process parameters?

Answer 16

The average chain length

Question 17

The degree of polymerisation DP represents the

Answer 17

average number of mer units in the chain

Question 18

A high DP means

Answer 18

the chains are longer therefore a high molecular weight

Question 19

A low DP means

Answer 19

the chains are shorter therefore a low molecular weight

Question 20

If a polymer is linear, what does it mean?

Answer 20

Close packed and neat linear chain structures

Question 21

Branched polymer, what does it mean?

Answer 21

the polymers during polymerisation become branched and cannot pack so closely together

Question 22

Copolymers consist of

Answer 22

chains with two different mer units that can be regularly or randomly arranged or formed into blocks

Question 23

Chains of different mer units can also be ——-

Answer 23

attached

Question 24

In a thermoplastic, how do they usually form a region of regular crystalline structure?

Answer 24

When the long chains fold and align

Question 25

The driving force for the thermoplastic forming a region of regular structure is%

Question 26

Cooling rate in a thermoplastic determined the

Answer 26

level of crystallinity

Question 27

Fast cooling = Slow cooling =

Answer 27

low crystallinity high crystallinity

Question 28

Spherulites are formed when

Answer 28

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

Question 29

What affects the way in which the chain molecules pack to for lamellae?

Answer 29

Arrangement of the side groups

Question 30

Large side groups can make ----- ------ difficult and also reduces ----- ------

Answer 30

crystal formation, chain mobility

Question 31

What is the term used to refer to a polymer with side groups all attached on one side of the C-C bonds?

Answer 31

Isotactic

Question 32

What is the term used to refer to a polymer with side groups attached on both sides, in alternating orders, of the C-C bonds?

Answer 32

Syndiotactic

Question 33

What is the term used to refer to a polymer with side groups attached on both sides of the C-C bonds with no specific order?

Answer 33

Atactic

Question 34

Higher crystallinity leads to:

Answer 34

- Higher melting point - Increased solvent resistance - Increased stiffness - Reduced permeation of gases - Light scattering - get opaque materials if crystals are large

Question 35

Cooling an amorphous polymer, what are the characteristics observed?

Answer 35

- No distinct solidification or crystallisation - Reformation of secondary bonds which limits motion of the motion of the particles --- material turns into a rubbery material - Once it has cooled right down below Tg, insufficient energy to break the secondary bonds --- material turns brittle and glassy

Question 36

Cooling a semi-crystalline polymer, what are the characteristics observed?

Answer 36

- Shows intermediate behaviour - Change in volume at Tm as some of the chains for lamellae - Amorphous regions between lamellae cease movement, around Tg it becomes glassy

Question 37

Tg =

Answer 37

glass transition temperature

Question 38

Tm =

Answer 38

melting temperature

Question 39

Yield strength for a polymer is defined at what point?

Answer 39

When the neck begins to form

Question 40

When tensile testing a thermoplastic, what sort of feature does it initially display?

Answer 40

Proportional stress/strain relationship

Question 41

As a polymer strip is put under a tensile test and is stretched, what happens to the fibres?

Answer 41

Initially they are jumbled up but as the force is applied and the neck begins to form, the fibres all line up

Question 42

Viscoelastic materials

Answer 42

exhibit elastic behaviour when loaded over a short time but will flow. appear viscous when loaded over a longer time

Question 43

For many polymers, creep can occur at

Answer 43

room temperature or just above

Question 44

Creep is

Answer 44

the deformation or stretching of polymers subjected to a constant stress, over a period of time

Question 45

The deflection temp of a polymer indicates the ....

Answer 45

likelihood of creep

Question 46

Mer unit of polyethylene

Answer 46

H H | | -C- C- | | H H

Question 47

Polyethylene is typically used in

Answer 47

bags, electrical equipment, bottles

Question 48

Few pros of polyethylene

Answer 48

- Low cost - Tough - Flexible - Corrosion resistant

Question 49

Mer unit of polypropylene

Answer 49

H H | | -C-C- | | H CH3

Question 50

Few pros of polypropylene

Answer 50

- Low cost - Tough - flexible - Stronger than PE and better at high temp

Question 51

Polypropylene is typically used in

Answer 51

packaging, pipes and fittings, chairs

Question 52

Mer unit of Polytetrafluoroethylene

Answer 52

F F | | -C-C- | | F F

Question 53

Typical uses for Polytetrafluoroethylene

Answer 53

gaskets, inert lab equipment, electrical insulation

Question 54

Pro of Polytetrafluoroethylene

Answer 54

low stick due to low surface energy

Question 55

Nylon is known for the chemical name of

Answer 55

polyamide

Question 56

Thermoset polymers -------- -- ----- once formed into a structure

Answer 56

cannot be reformed

Question 57

Thermoset polymers are better than thermoplastics due to the reasons that they have a ..... and .....

Answer 57

good chemical resistance and higher operating temperature

Question 58

3 examples of thermoset polymers

Answer 58

- Phenol-formaldehyde - Urea-formaldehyde - Melamine-formaldehyde

Question 59

As thermoset polymers are linked together with ----- ------ ------, the material does not show many variations in properties .......

Answer 59

strong covalent bonds, with temperature as thermoplastics do

Question 60

Two things oberved about thermoset polymers that are not oberved in thermoplastics

Answer 60

- Very little softening occurs when raised to a high temperature, too high and the material begins to degrade - Tg is usually high, won't "flow" but will become more compliant

Question 61

What are the characteristics to an elastomer when put under a straining force?

Answer 61

- All deformation is elastic - no plastic deformation - Bonds stretched as more force is applied to the material - Sudden failure is seen

Question 62

Thermoset elastometers have only a few....

Answer 62

cross links joining the polymer chains together

Question 63

Silicones have ----- ------ but made up of Si-O

Answer 63

long chains

Question 64

Polymer additives are

Answer 64

additional materials which are mixed into a polymer to change its mechanical properties, such as strength and wearability etc...

Question 65

Filler additives are those added to

Answer 65

improve; - tensile and compressive strength - abrasion resisitance - toughness - dimensional stability

Question 66

Plasticiser additives are

Answer 66

small molecules added to a polymer which obstruct the secondary bonding between molecules

Question 67

Stabiliser additives are added to

Answer 67

prevent deterioration of the polymer in service due to exposure to light and atmosphere

Question 68

Stabiliser additives can reduce the chance of

Answer 68

- colour change - deterioration of mechanical properties - cracking - surface crazing - UV bond breakage

Question 69

------- ------- are added to polymers to reduce the flammability of the organic materials

Answer 69

Flame retardants