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radical polymerization

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Rayan:
Hello,
I hope i'm posting this in the right form..
Well i'd like to ask about the kinetics of a radical polymerization; i found in my course that we suppose that the rate of formation of the free radicals is equal to their rate of consumption, and that's because the terminating constant is much greater than the initating constant.
Here's my question: if the terminating constant is much bigger then the initiating constant, then why do polymerization still occur?
thanks in advance

ps: i hope i'm speaking correct english. i had trouble translating this from french..

Mitch:
Because the polymerization is not reversible

agrobert:
Also, not all termination steps are unfavorable.  For example in radical chlorination Cl. can attack Cl. but Cl. can be regenerated from Cl2.

Rayan:
are there any other factors that also affect the polymerization?

P:

--- Quote from: Rayan on November 06, 2007, 02:57:17 PM ---Here's my question: if the terminating constant is much bigger then the initiating constant, then why do polymerization still occur?
thanks in advance

--- End quote ---

To terminate the radicals have to collide with each other - if two radicals meet then they will terminate.  Until they actually meet however (conc. is low compared to the monomer) they will whizz around reacting with monomer until two radical chain ends come into close enough proximity for a termination reaction to take place.


--- Quote from: Rayan on November 11, 2007, 12:24:51 PM ---are there any other factors that also affect the polymerization?

--- End quote ---

look up chain transfer.

PS: Some factors which effect polymerisations are: Temp, Solvent Conc., type of solvent, atmosphere (some need to be oxygen free and thus are degassed first).

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