Addition polymerisation. (1 Viewer)

[undalay]

Okay so we all know that in the formation of LDPE the initiator, usually an organise peroxide, becomes part of the end polymer.

For the ziegler-natta process:

1. Does it become part of the end polymer?
2. How does termination occur for the ziegler-natta process?
3. How exactly does the process itself work?

Thx for your help : D

 

[cameron0110]

I'm fairly sure that the ziegler natta process doesn't need an initiator.

What happens is that the alkene binds to the metal catalyst and an alkyl group is added (cause funny stuff happens at metal surfaces). This then gives the propagating polymer chain and a vacancy for another alkene to bind and so it continues. Termination occurs when the 2nd hydrogen of the growing polymer chain is removed by the metal (again, metal surfaces do weird stuff) which gives the polymer you want but with a double bond at the end.

So basically instead of the initiator ending up at the end of the polymer, you just get a double bond. Like everything in life, wikipedia has some decent stuff on this.

 

[undalay]

what's the difference between the catalyst (the metal) and an initiator?

 

[cameron0110]

The initiator is used in the reaction (you need one for every polymer chain you want to create) while the catalyst is not used up in the reaction so in principle it can be reused.

Also the initiator becomes part of the finished polymer while the metal catalyst doesn't. Hope that helps.

 

[benji6667]

ill try and re-call this from vague memory

-the Zieglar-natta process does not become a part of the polymer at the end as it uses a catalyst (such as triethylaluminium)

-termination occues when the catalyst is removed, the monomer units are consumed, the conditions are no longer met (ie pressure, temperate) or two activated chains collide to form one chain (and effectively terminating that chain)

hope this helps

-

 

[minijumbuk]

How can you start and end a polyethene chain with 2 ethene molecules? Don't the ethene molecules already have 4 bonds? So how can it bond with the beginning and end of the chain?

 

[Red-Ink-Frenzy]

How can you start and end a polyethene chain with 2 ethene molecules? Don't the ethene molecules already have 4 bonds? So how can it bond with the beginning and end of the chain?

Polymerisation of ethylene is an addition reaction, therefore the double bonds break into single bonds.

The intiator creates an activated ethylene molecule (by attaching to it), and is used in the reaction (unlike a catalyst).

Propagation occurs when the 'activated' molecule connects with an ordinary ethylene open bond, making the chain longer.

Termination occurs when two activated chains collide; they join to form a stable polymer molecule or exchange an H atom to form two stable molecules

Hope this answers your question.

 

[minijumbuk]

No, I mean in the catalysed Ziegler-Natta process, the production of HDPE as cameron0110 described.