A - Polymers

Question 1

What is a condensation reaction?

Answer 1

A reaction where two molecules react together and a small molecule, mostly water (but could be HCl), is eliminated.

Question 2

What does condensation polymerisation usually involve?

Answer 2

Usually involves two different types of monomer, each with at least two functional groups.

Each functional group reacts with a group on another monomer to form a link, creating polymer chains.

Each time a link is formed, a small molecule is lost (water).

Question 3

Give some examples of condensation polymers.

Answer 3

Polyamides, polyesters, polypeptides and proteins.

Question 4

How can you form a polyamide?

Answer 4

By reacting a dicarboxylic acid with a diamine.

Question 5

What is a dicarboxylic acid?

Answer 5

A molecule with two carboxylic acid groups.

Question 6

What is a diamine?

Answer 6

A molecule with two amine groups.

Question 7

What is repeated in a polyamide?

Answer 7

The amide linkage -CONH- is repeated over and over.

Question 8

Outline what happens, and what is formed, in the condensation polymerisation reaction between a dicarboxylic acid and a diamine.

Answer 8

The carboxyl group of the dicarboxylic acid reacts with the amino group of the diamine to form amide links in the polyamide.

Dicarboxylic acids and diamines have functional groups at each end of the molecule, so long chains can form.

A water molecule is eliminated with each amide link formed.

Question 9

Give two examples of polyamides.

Answer 9

1. Nylon 6,6

2. Kevlar

Question 10

What are the monomers that make up nylon 6,6?

Answer 10

1,6-diaminohexane and hexanedioic acid.

Question 11

What is the formula for 1,6-diaminohexane?

Answer 11

H2N(CH2)6NH2

Question 12

What is the formula for hexanedioic acid?

Answer 12

HOCO(CH2)4OCOH

Question 13

What is the formula for nylon 6,6? What is the repeating unit?

Answer 13

[HN(CH2)6NHCO(CH2)4CO]n

The repeating unit is the bit inside the square brackets.

Question 14

What are the monomers that make up Kevlar?

Answer 14

1,4-diaminobenzene and benzene-1,4-dicarboxylic acid.

Question 15

What is the formula for 1,4-diaminobenzene?

Answer 15

H2N(benzene ring)NH2

Question 16

What is the formula for benzene-1,4-dicarboxylic acid?

Answer 16

HOOC(benzene ring)COOH

Question 17

What is the formula for Kevlar? What is the repeating unit?

Answer 17

[HN(benzene ring)NHCO(benzene ring)CO]n

The repeating unit is the bit inside the square brackets.

Question 18

What are some typical uses of nylon 6,6?

Answer 18

Used to make clothing, carpet, rope, airbags and parachutes.

Question 19

What are some typical uses of Kevlar?

Answer 19

Used in bulletproof vests, boat construction, car tyres and lightweight sports equipment.

Question 20

Why is Kevlar so strong?

Answer 20

Due to the rigid chains and the ability of the flat aromatic rings to pack together held by strong intermolecular forces.

Question 21

How are polyesters formed?

Answer 21

By a reaction between dicarboxylic acids and diols.

Question 22

Outline the condensation polymerisation reaction, and the products formed, between dicarboxylic acids and diols.

Answer 22

The carboxyl groups of dicarboxylic acids react with the hydroxyl groups of diols to form ester links to form polyesters.

Water is eliminated with each ester link formed.

Question 23

Give an example of a polyester.

Answer 23

Terylene (PET).

Question 24

What monomers form Terylene (PET)?

Answer 24

Benzene-1,4-dicarboxylic acid and ethane-1,2-diol.

Question 25

What are the typical uses of Terylene (PET)?

Answer 25

Used in plastic bottles, clothing, sheets and sails.

Question 26

Explain the nature of the intermolecular forces between molecules of condensation polymers.

Answer 26

Condensation polymers are generally stronger and more rigid than addition polymers.

This is because condensation polymers are made up of chains containing polar bonds, e.g C-N and C-O. So there are hydrogen bonds between the polymer chains, as well as permanent dipole-dipole forces and Van der Waals forces which are also present.

Question 27

How do you identify the repeating unit of a condensation polymer?

Answer 27

This is found by starting at any point in the polymer and stopping when the same pattern of atom begins again.

Question 28

How do you identify the monomer(s) of a condensation polymer?

Answer 28

1. Start with the repeating unit.
2. Break the linkage (at the C-O for a polyester or C-N for a polyamide).
3. Add back the components of water for each ester or amide link.

Question 29

Why are polyalkenes chemically inert and non-biodegradable? Give some examples of polyalkenes.

Answer 29

They are addition polymers made up of non-polar carbon chains. This is what makes them unreactive and chemically inert, and non-biodegradable.

Examples: poly(ethene) and polystyrene.

Question 30

Why are condensation polymers biodegradable? Do they degrade quickly?

Answer 30

They have polar bonds in their chains, which makes them open to attack from nucleophiles. This means that they can be broken down by hydrolysis and are biodegradable, although this process is very slow.

Question 31

Why is the question about how we dispose of plastics (synthetic polymers) so important?

Answer 31

Because plastics either take a very long time to biodegrade or are non-biodegradable.

Question 32

What are the four options of disposing of plastics?

Answer 32

1. Burying
2. Burning
3. Reusing
4. Recycling

Question 33

When are plastics sent to the landfill to be buried?

Answer 33

When the plastic is:

1. Difficult to separate from other waste
2. Not in sufficient quantities to make separation financially worthwhile
3. Too difficult technically to recycle.

Question 34

What are the pros and cons of using the landfill to bury plastics?

Answer 34

Pros:
1. It’s relatively cheap and easy method of waste disposal.

Cons:

1. Required areas of land.
2. As waste decomposes, it can release methane (a greenhouse gas).
3. Leaks from landfill sites can contaminate water supplies.
4. We’re producing large amounts of waste so there is a need to reduce landfill as much as possible.

Question 35

Discuss burning as a method of plastic disposal.

Answer 35

Waste plastics can be burned and the heat can be used to generate electricity.

This process must be controlled to reduce the release of toxic gases e.g polymers containing chlorine, such as PVC, produce HCl when burned which is toxic and must be removed.

Waste gases from the combustion are passed through scrubbers to do this which can neutralises gases such as HCl by allowing them to react with a base.

But waste gases such as CO2 still contribute to the greenhouse effect.

Question 36

After sorting plastics, what are the different methods of recycling them?

Answer 36

1. Some plastics, such as poly(propane) for example, can be melted and remoulded.
2. Some plastics can be cracked into monomers, and these can be used to make more plastics or other chemicals.

Question 37

What are the advantages of recycling?

Answer 37

1. Reduces amount of waste going to landfill.
2. Saves raw materials (important as oil is non-renewable).
3. Cost of recycling plastics is lower than making plastics from scratch.
4. Produces less CO2 emissions than burning plastics.

Question 38

What are the disadvantages of recycling plastics?

Answer 38

1. It’s technically difficult.
2. Collecting, sorting and processing the plastic is more expensive than burning/landfill.
3. You often can’t remake the plastic you started with, you have to make something else.
4. The plastic can be easily contaminated during the recycling process.