Synthetic Polymers

5 marks · Easy

Poly(chloroethene) is better known as PVC and is used for making pipes and insulation.

(a)

Describe briefly how an addition polymer such as poly(chloroethene) is prepared from its monomer.

[2 marks]

(b)

Draw the structural formula of the monomer used to make poly(chloroethene).

[1 mark]

(c)

The displayed formula of a polymer chain is shown below:

Deduce the name and displayed formula of the alkene monomer used to make this polymer.

[2 marks]

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) Addition polymers are produced by joining many small alkene molecules (monomers) together. Under heat and high pressure, the double bond in each monomer opens up, forming a long chain with single bonds only. · must show Monomers (alkenes) join together, Double bond opens; long chain forms

(b) Displayed formula for chloroethene: CH2=CHCl · must show Double bond between two carbons, Cl attached to one carbon, H atoms correctly placed

(c) Monomer is propene, displayed as CH2=CH–CH3 or (H2C=CH-CH3) · must show Name: propene, Displayed or structural formula: CH2=CHCH3

Common mistakes: saying water is produced; omitting the double bond in the monomer; giving polymer instead of monomer name

Show mark scheme and worked solution

Marking points

M1 (a) · 1 mark · Describes joining of many alkene monomers (small molecules).

M2 (a) · 1 mark · Mentions double bond opens to allow joining/forming single bonds/long chain.

B1 (b) · 1 mark · Draws correct displayed/structural formula of chloroethene (CH2=CHCl).

B2 (c) · 1 mark · Gives correct name (propene) for the monomer.

B3 (c) · 1 mark · Gives correct displayed/structural formula: CH2=CHCH3 or H2C=CH–CH3.

Worked solution

a) Addition polymerisation involves lots of small molecules, monomers (such as alkene molecules), joining together. The double bond in the monomer opens up so molecules can link into a chain without anything else being formed.

b) The monomer for poly(chloroethene) is chloroethene (vinyl chloride). Its displayed formula is:

c) The repeat unit —[CH2–CH(CH3)]— comes from the monomer propene. The displayed formula for propene is: