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Topic: Behaviour of Vazo 68 initiator in polymerisation  (Read 3448 times)

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Offline charzhino

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Behaviour of Vazo 68 initiator in polymerisation
« on: January 17, 2012, 05:58:27 AM »
I am using Vazo 68 (4,4-azobis cyanovaleric acid) in the homopolymerization of methacrylic acid. Vaz0 68 has to be stored at around 5 oC. The reaction generally proceeds with adding the Vazo and monomer to deionized water (which has been boiled beforehand to remove additional dissolved oxygen) at room temperature, then heating the reaction to 74 oC. Due to efficiency and time issues how would the reaction be affected if instead of boiling the water and waited for it to cool, I heated it to 45-50 oC and let the steam escape for around 30 minutes. Then instead of letting it cool, I added the monomer and initiator at 45 oC and heated to the target temperature of 74 oC.

My main goal is to achieve a specific viscosity on the final polymer, if that helps. If anyone can help on the chemistry that could take place in regards to the initiator that would be appreciated. I am thinking that the Vazo molecules may dissociate and recombine quicker at 40 oC, thus reducing the rate of polymerisation. The half-life of Vazo at 60 oC is 10 hours if that helps. Thanks.

Offline fledarmus

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Re: Behaviour of Vazo 68 initiator in polymerisation
« Reply #1 on: January 17, 2012, 08:12:32 AM »
The purpose of boiling the water is to deoxygenate the water? There are other ways...

One would be to pull a vacuum on the system so the water boils at a lower temperature.

Another way would be to bubble an inert gas such as nitrogen through the water.

The problem with just heating to a lower temperature is that you are concerned with the solubility of the oxygen in the water. The solubility decreases as the temperature of the water increases, or as the pressure above the water decreases. Although you will have less dissolved oxygen at 45-50C, it will still be more than you would have at 100C, or at a pressure which would boil your water at 45-50C.

Offline jaspevacek

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Re: Behaviour of Vazo 68 initiator in polymerisation
« Reply #2 on: January 18, 2012, 02:47:58 PM »
Unless you are overly concerned with the kinetics of the reaction (i.e., if that is the whole point of the experiment), then ignore the oxygen or add a little more initiator.

Regarding your other questions: the initiator undergoes thermal homolysis - heat splits it in two identical parts, one on each side of the azo group, thus forming nitrogen and two radicals. Cage effects (the dissociation and recombination that you mentioned) are more of a concern with Vazo 64 (AIBN).

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