WHY do alkene molecules join together in polymerisation?

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Niamh Baines
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I have an exam question on this. I know how polymerisation works but i dont know why alkene molecules are able to join together. Please help
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Torel
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They join together due to the addition of a free radical.

This stems from the reaction of Ethene with oxygen, causing an Ethene free radical, this then causes a chain reaction when Ethene free radicals meet with ethene molecules.

This is because of the way the pi bond works and the fact that the free radical addition gives a stronger bond than the pi bond that already exists, thus making the molecule more stable.

(I just used Ethene, as personally I can conceptualise that more easily)
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charco
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(Original post by Niamh Baines)
I have an exam question on this. I know how polymerisation works but i dont know why alkene molecules are able to join together. Please help
While the explanation above is correct for oxygen catalysed addition polymerisation, nowadays this is carried out using a Zeigler-Natta catalyst, which gives more control over the type of polymer produced (isotactic rather than atactic).

Here's a small interactive showing addition polymerisation that may help
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Niamh Baines
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Thank u so much
(Original post by Torel)
They join together due to the addition of a free radical.

This stems from the reaction of Ethene with oxygen, causing an Ethene free radical, this then causes a chain reaction when Ethene free radicals meet with ethene molecules.

This is because of the way the pi bond works and the fact that the free radical addition gives a stronger bond than the pi bond that already exists, thus making the molecule more stable.

(I just used Ethene, as personally I can conceptualise that more easily)
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Niamh Baines
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Thanks u really helped

(Original post by charco)
While the explanation above is correct for oxygen catalysed addition polymerisation, nowadays this is carried out using a Zeigler-Natta catalyst, which gives more control over the type of polymer produced (isotactic rather than atactic).

Here's a small interactive showing addition polymerisation that may help
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