Polymers

Question 1

What is a polymer?

Answer 1

A polymer is an organic material made by joining many Mers with covalent bond to produce chain like structures.

Question 1

What is a homopolymer?

Answer 1

homopolymers are when all the repeating units are the same type.

Question 2

What is a copolymers?

Answer 2

Is a Polymers made from more than one type of monomer.

Question 3

What is a functional group?

Answer 3

A functional group is a specific group of atoms within a molecule that is responsible for a characteristic chemical reaction of that molecule.

Question 4

What are the mechanisms of Polymerisation and what do they require?

Answer 4

Addition which required unsaturated bond and a catalyst and Condensation which requires reactive groups at the end of the monomer.

Question 5

Why is molecular weight important?

Answer 5

Not all chain grow to the same length so the properties of the polymers will be affected by its molecular weight.

Question 6

How does bond rotation affect polymers?

Answer 6

The covalent bond in a polymer is directional so they can like any direction as long as they are angled at 109 degrees meaning the polymer can form in different shapes.

Question 7

Why are additives used in polymers?

Answer 7

Additives are used to improve the mechanical properties of the polymer.

Question 8

What are fillers?

Answer 8

Fillers are a group of additives usually used to increase the compressive and tensile strength, hardness and toughness.

Question 9

What are some types of additives?

Answer 9

Colourants, Flame Retardants and Plasticiser.

Question 10

What are the different polymer chains?

Answer 10

Linear, Branched, Cross linked, Networked.

Question 11

What is the difference between thermoplastics, thermosets and Elastomers?

Answer 11

Thermoplastics do melt, Thermosets do not melt and elastomers are special in that they are highly elastic.

Question 12

What is isomerism?

Answer 12

Different atomic configuration for the same composition.

Question 13

What are Stereoisomers?

Answer 13

Molecules linked in the same order but differ in spacial arrangement.

Question 14

What are the stereoisomers configurations?

Answer 14

Isotactic (R on same side), Syndiotactic ( R alternate sides), Atactic( R is Random)

Question 15

What are the types of copolymers?

Answer 15

Random, Alternating, Block and Graft.

Question 16

What is Crystallinity?

Answer 16

The arrangement of atoms or molecules into an ordered structure.

Question 17

How is the degree of crystallinity affected?

Answer 17

Size of the side groups, intermolecular forces, steric regularity.

streic regularity is how difficult different stereoisomer configeration are to crystallise

Question 18

What is the glass transition temperature?

Answer 18

The glass transition temperature (Tg) is the temperature at which an amorphous material transitions from a hard, brittle state into a softer, more rubbery state.

Question 19

What are the stages of deformation?

Answer 19

Crystalline lamellae ‘shear’ past each other, lamellae orientate to the load direction, lamellae segments separate from the bulk connected by tie chains, Blocks and tie chains align with the loading direction.

Question 20

What are the effects of crosslinking in a structure?

Answer 20

increased strength and stiffness, reduced ductility

Question 21

What increases the melting point of a material?

Answer 21

Reducing branching, increased molecular weight, crystallite size and larger/stiffer backbone units and side groups.

Question 22

What is the difference between purely elastic behaviour and purely viscous behaviour?

Answer 22

An elastic material will “spring” back to it original form when the load is removed, when the load is applied to a viscous material the strain will increase over time until it is removed.

Question 23

What are the steps in a general shaping process?

Answer 23

Production of liquid, placement of material/liquid, hardening

Question 24

How does the shaping process differ for thermoplastic and thermosets?

Answer 24

For thermoplastics we heat above Tg, shape, then cool. For thermosets we have a low viscosity liquid when mixed, shape and then possibly have to heat to cure.

Question 25

What is shaping by extrusion?

Answer 25

Extrusion is use to make continuous products of constant cross section (eg, sheets of pipes).

Question 26

What is shaping by moulding?

Answer 26

There are many forms of moulding but generally moulding is get a material/liquid and putting is around a shape in a specific way.

Question 27

What is shaping by joining?

Answer 27

Joining can be done mechanically, by welding or by adhesive bonding.

Question 28

What is Exotherm?

Answer 28

Is the process of thermoset curing and there is a large amount of heat released?

Question 29

What are macromolecules

Answer 29

Because there is a very large amount of monomers making up a polymer chain, polymers are commonly termed macromolecules.

Question 30

What are the main differences between condensation polymerisation and addition polymerisation

Answer 30

Condensation produces a byproduct of H20 each time a monomer joins the chain, Addition reactions involve radicals and a change of boding instead of a loss of atoms to by-products.

Question 31

What is the viscoelastic behaviour in a leathery state?

Answer 31

Small instantaneous elastic strain followed by a much larger time-dependent elastic strain along with a small amount of viscous flow

Question 32

What is the viscoelastic behaviour in a rubbery state?

Answer 32

More instantaneous elastic strain, negligible primary creep, and increased viscous flow

Question 33

Explain the 5 stages of a more realistic viscoelastic behaviour.

Answer 33

1) Rapid elastic loading
2) Primary and secondary creep occurring
3) Rapid elastic recovery
4) Slow recovery of primary creep
5) No recovery of secondary creep

Question 34

What happens to a semi-crystalline thermoplastic polymer material when a polymer is heated past the Tg, Tm, Td.

Answer 34

Tg: amorphous regions get out of their glass-like state, and secondary bonds break.
Tm: The secondary bond holding the crystalline region together breaks.
Td: the primary covalent bond break.

Question 35

How does the addition of plasticisers affect the mechanical properties of a polymer?

Answer 35

Plasticisers are used to reduce the stiffness and increase the “flexibility” and/or “softness” of a polymer. They work by lowering the glass transition temperature of the polymer.