Does anyone know the procedure of removing the inhibitor from the monomer acrylic acid? Is it necessary to do so in order to achieve polymerization?
Liquid monomers are always stabilized before shipping to increase their shelve-life. This is achieved by introducing few ppm of a radical-scavenging compound, usually a hidroquinone or catechol derivatives. It is usually taken off before polymerization, otherwise it will react with the free radical initiator at early time reducing hence their efficiency and concentration, so if it remains a part it will launch the polymerization but the conversion and ultimate molecular weight became unpredictable.
To remove the inhibitor there are two major techniques used without any problems:
- one is by passing the liquid monomer througn a column filled with silica or alumina gels
- and the second is by washing with a concentrated solution of NaOH (4N), followed by drying (dehydrating agent) and sometimes distilled under reduced pressure
To tell you, this situation is already discussed in the area of the researchgate.
Liquid monomers are always stabilized before shipping to increase their shelve-life. This is achieved by introducing few ppm of a radical-scavenging compound, usually a hidroquinone or catechol derivatives. It is usually taken off before polymerization, otherwise it will react with the free radical initiator at early time reducing hence their efficiency and concentration, so if it remains a part it will launch the polymerization but the conversion and ultimate molecular weight became unpredictable.
To remove the inhibitor there are two major techniques used without any problems:
- one is by passing the liquid monomer througn a column filled with silica or alumina gels
- and the second is by washing with a concentrated solution of NaOH (4N), followed by drying (dehydrating agent) and sometimes distilled under reduced pressure
To tell you, this situation is already discussed in the area of the researchgate.
In industrial grade there is no need for removing the inhibitors and in order to solve this problem higher amount of initiator can be used. but for higher accuracy work you can use vacuum distillation in addition to methods that Abdelkader BOUAZIZ mentioned.
Distill it through a column/condenser filled with copper turning.
or add copper sulfate and distill
Boiling point of acrylic acid is high, Rate of propagation is very high and can not be washed with NaOH because it is soluble in water. the best way is to stir it over active alumina for 24H at RT
The best method that works for us is a distillation under reduced pressure with copper wire, shavings or foil (clean, shiny surface is essential) in the distillation flask, not in the condenser or the receiving flask. In this way any radicals forming during the heating of the distillation flask are quenched. After the distillation you should store any unused portion at -4oC, but not for a long time. Good luck.
I think the answers given above cover the topic already. Alternatively, you can check how other researchers that determined kinetics of the polymerization reaction did this, e.g. Cutie et al. Journal of Polymer Science Part B: Polymer Physics
Volume 35, Issue 13, pages 2029–2047, 30 September 1997. But, they also did not remove the inhibitor first.
For our studies we use PA grade acrylic acid with 50ppm MEHQ as delivered and compensated for that with the initiatior dosage.
If you really want to remove inhibitor, please handle with great care. Acrylic acid in the purest form can be subject of fast almost explosive polymerization when heated or when incidental impurities trigger the reaction.
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