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Describe the steps involved in the process of addition polymerisation - HSC - SSCE Chemistry - Question 25 - 2015 - Paper 1
Question 25
Describe the steps involved in the process of addition polymerisation. Explain the uses of polyethylene and polystyrene in terms of their structures and properties.
Worked Solution & Example Answer:Describe the steps involved in the process of addition polymerisation - HSC - SSCE Chemistry - Question 25 - 2015 - Paper 1
Step 1
Describe the steps involved in the process of addition polymerisation.
Answer
The process of addition polymerisation involves three main steps: initiation, propagation, and termination.
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Initiation: The reaction begins when an initiator, such as an organic peroxide, attacks an ethylene molecule. This action breaks the double bond, producing an unpaired reactive electron on the end of the growing chain.
H H H I C = C → I C• H H H -
Propagation: The newly formed reactive species will then attack another ethylene molecule, leading to an increase in the length of the growing polymer chain. This process continues as each successive ethylene molecule joins the chain.
H H H H H H I C• + C = C → I C - C - C • H H H H H H -
Termination: The chain length continues to grow until two growing chains combine or a terminating agent is involved, leading to the formation of a stable polymer.
H H H H H I C - C + C - C → I C - C - C - C H H H H H
Step 2
Explain the uses of polyethylene and polystyrene in terms of their structures and properties.
Answer
Polyethylene and polystyrene are widely used polymers, each with distinct properties influenced by their structures.
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Polyethylene: Composed of long carbon chains, polyethylene is flexible and has low density. This structure allows it to be used in a variety of applications, such as cling wrap and milk bottles, due to its flexibility and lightweight nature.
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Polystyrene: Polystyrene consists of long carbon chains with benzene rings attached. This structure gives it rigidity, making it suitable for use in manufacturing products like cutlery and food containers. It can also be utilized as insulation in construction, owing to its strength and thermal resistance.