Addition polymerisation

4 marks · Normal

Poly(ethene) is made from ethene by addition polymerisation.

(a)

Describe the conditions required for the polymerisation of ethene.

[1 mark]

(b)

Write the chemical equation, using displayed formulae, for the formation of poly(ethene) from ethene.

[2 marks]

(c)

Explain why nothing else is produced in this reaction.

[1 mark]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

(a) High temperature, high pressure, and an initiator · must show Mentions heat OR high temperature AND high pressure AND/OR initiator

(b) n H2C=CH2 → (—CH2—CH2—)n (using displayed formulae/brackets) · must show Correct displayed formulae of both monomer and polymer (with n and polymer brackets), No other products shown

(c) No other substances are produced because all atoms in the ethene molecules are used to make the polymer. · must show Mentions that all atoms from the monomer are used in the polymer OR that addition polymerisation only joins molecules together

Common mistakes: Saying catalyst instead of initiator

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · States high temperature or heat AND high pressure (accept initiator)

M1 (b) · 1 mark · Uses correct displayed formulae (at least for ethene) and brackets for polymer

A1 (b) · 1 mark · Shows correct number of monomers (n) and no other products in the equation

B2 (c) · 1 mark · Explains that all atoms in the monomer go into the polymer, so nothing else is formed

Worked solution

a) Ethene is polymerised at high temperature, under high pressure, and in the presence of an initiator.

b) The displayed formula would be:

c) Nothing else is produced because in addition polymerisation, the double bonds in the monomers open to form a single chain; all atoms from the ethene are used in the polymer chain.