1. Polymerisation

Question 1

Name some natural polymers

Answer 1

Wool, cotton, wood and rubber

Question 2

What is monomer?

Answer 2

A small molecule. Many monomer molecules can be joined together to form a long chain of repeating unites called a polymer.

Question 3

What is a polymer?

Answer 3

A large molecule consisting of a large number of identical small molecules (monomers).

Question 4

Name some examples of polymers

Answer 4

Plastics, rubbers, starch, cellulose and protein

Question 5

Define polymerization

Answer 5

Process by which monomers are converted to polymers

Question 6

Why is ethene used more extensively in industry than ethane?

Answer 6

Ethene is more reactive due to double bond.

Question 7

Why are synthetic polymers replacing natural polymers?

Answer 7

• Cheaper

- Better suited to particular function as chemist can produce polymers suitable to specifications.

Question 8

What is LDPE and HDPE respectively?

Answer 8

Low and High Density Polyethylene

Question 9

What type of monomers are involved in addition polymerisation?

Answer 9

Double bonded monomers.

Question 10

What are the two processes to make polyethylene?

Answer 10

• Initiator: Heating for LDPE

- Surface catalyst: Ziegler Natta 1950 for HDPE

Question 11

What are the requirements for producing LDPE?

Answer 11

• Heat at 300 degrees celsius
• Initiator such as peroxide or oxygen
• High pressure of 1000- 3000atm

Question 12

What are the consequences for producing LDPE using an initiator?

Answer 12

• It has branched chains and can be easily deformed.

Question 13

Define free radical

Answer 13

A species with an unpaired outer shell electron

Question 14

What is the free radical’s role in the formation of a polymer?

Answer 14

• Free radical is reactive

- Radical free ethene molecules can readily join together.

Question 15

What happens during intiation?

Answer 15

• Initiator (Benzoyl peroxide) molecule is heated to form peroxide free radicals.

Question 16

What happens during activation?

Answer 16

• Free radicals combine with some monomers.

- Monomers become activated.

Question 17

What happens during Propagation?

Answer 17

• Activated monomers react with more ethylene monomers to increase its chain length.
• Some branching occurs as chain growth- the radical end often curl on existing chain and removes hydrogen atom.

Question 18

What happens during Termination?

Answer 18

Process of chain growth terminates as free radicals combine to form a non- activated species.

Question 19

What else can cause Termination?

Answer 19

Inhibitors, lowering pressure and temperature.

Question 20

Define a Dimer

Answer 20

A molecule with same functional group at the ends.

Question 21

What is used in the production of HDPE?

Answer 21

Chronimium oxide.

Question 22

What gives HDPE extra strength?

Answer 22

Varying pressure can cause cross linking between polymer chains which adds strength.

Question 23

How is the Zieglar Natta method carried out?

Answer 23

• Ethylene gas is passed through a liquid alkane solution (at 60 degrees celsius) at 1 atm.
• With tiny amounts of catalyst, titanium chloride and triethyl aluminium chloride.

Question 24

What is the Zieglar Natta catalyst?

Answer 24

Titanium chloride and triethyl aluminium chloride

Question 25

What is the effect of cross- linked polymer chains?

Answer 25

• Enhances rigidity

- Melting point enhances

Question 26

Why is it important to measure the temperature of the reaction during the production of polyethylene?

Answer 26

• Heat could make polyethylene decompose as it forms, thus decreasing yield.

Question 27

How many monomer units does polyvinyl chloride (PVC) have?

Answer 27

400 - 4000

Question 28

What’s the systematic and common name for PVC monomers?

Answer 28

Systematic: Chloroethene.

Common: Vinyl Chloride

Question 29

Plastiser + PVC?

Answer 29

Decreases dispersion forces. Polymer becomes more flexible.

Question 30

UV absorber + PVC?

Answer 30

Prevents UV decomposition of plastic.

Question 31

Heat stabiliser + PVC?

Answer 31

Decomposes above 80C.

- Adding heat stabilizer would improve its resistance to heat decomposition.

Question 32

What are addition polymers?

Answer 32

Polymers that can be formed from an addition reaction involving many molecules of one or more monomers in double bonds.

Question 33

Describe the effect of the Zieglar Natta catalyst.

Answer 33

• Allows process to be carried out at lower temperatures

- Effect the arrangements of units attached to main chain and thus effects density and stability to heat.

Question 34

What is the common and systematic monomer name for Polystyrene?

Answer 34

Common: Styrene (Vinyl Benzene)

Systematic: Ethenylbenzene

Question 35

Which polymerisation process is used to make polyethylene?

Answer 35

Addition polymerisation

(Polymerisation using an initiaitor)

Question 36

Why is HDPE rigid and hard?

Answer 36

HDPE has less branching which allows the polymers to be arranged orderly on top of each other. This crystallines the HDPE and thus, has a white or transcluscent colour.

Question 37

Why is LDPE flexible?

Answer 37

The initiation polymerisation produces a lot of branching in its LDPEs. This branching prevents orderly arrangements of polymers which allows space for light to seep through or can be easily separated.