Hey, guys! Take a look at this white crystalline powder with a faint odour of benzaldehyde,
that I’ll use for today’s chemical reactions.
This is dry benzoyl peroxide.
Besides being used as a remedy for pimples,
it also used as a source of free phenyl radicals in organic chemistry,
which, in its turn, makes it a widely-used radical initiator in the chemistry of polymer synthesis.
When dry benzoyl peroxide heated above its melting point (~100°C),
instantaneous and explosive decomposition occurs without flame,
but the decomposition products are flammable.
Let’s put a little bit of benzoyl peroxide on a hot plate and see, what will happen
Slightly wet benzoyl peroxide is used in filmmaking to simulate the explosions of big volumes of fuel products,
because setting this kind of reagent on fire results in the production of rich flame and soot.
A commercially available reagent usually contains 25% water
Such benzoyl peroxide is resistant to physical impact and hard to set on fire with a naked flame
Benzoyl peroxide is incompatible with most of organic compounds of the amines class
So, for instance, the book "Reactive chemical hazards" says,
that addition of a drop of aniline to 1 gramm of the benzoyl peroxide
leads to mildly explosive decomposition after a short delay.
Well, let’s test it!
Yeah, it really is so, but I went one step further and decided to find out, what will happen,
if I add a much more reactive Phenylhydrazine.
And this is a reaction with trimethylamine
Well, now I’ll showcase radical polymerization, using benzoyl peroxide.
So, guys, this is methylacrylate
methylacrylate is an organic compaund, the methyl ester of acrylic acid
Its lable says, that it is stabilised with hydroquinone monomethyl ether
This substance prevents its autopolymerization, which allows it being stored for a long time
without any changes.
To perform the polymerization reaction, we need to get rid of this stabilizer.
It can be done by adding a little amount of alkali dilute solution
As a result, we got stabilizer-free methylacrylate
Then it needs to be distilled, as it’s a bit soluble in water,
although this won’t influence the demonstration of the reaction in any way.
Now I’ll transfer the upper layer of methylacrylate in another test-tube and add a little bit of benzoyl peroxide
Benzoyl peroxide starts to decompose into free radicals at a temperature of more than 60°C,
so, in order to initiate the reaction, we need to heat the test-tube.
Now you’re seeing radical polymerization,
that resembles boiling
Forming gas bubbles represent carbon dioxide
So, when we heat methylacrylate with benzoyl peroxide,
benzoyl peroxide free phenyl radicals and carbon dioxide
This step is called initiation
After the radical initiator is formed,
it attacks a monomer.
During initiation, an active center is created,
from which a polymer chain is generated.
the chain propagates until there are no more monomers
As radicals continue to grow, the system’s viscosity increases.
With this increase, the life span of macro radicals increases too,
which leads to the acceleration of polymerization at a late step,
due to the concentration of said macro radicals.
That late step of polymerization is taking place right now.
Therefore, you can see transparent, jellylike methyl acrylate polymer gather in the test-tube.
By the way, this reaction can be initiated by irradiating methylacrylate and benzoyl peroxide
with a 450nm blue laser diode.
Now let’s take a newly formed polymer out of the test-tube
Take a look at this soft, sticky, stretchy material
Polymethylacrylate is destructed at 250 °С,
forming carbon dioxide, methanol and low molecular weight polymers,
that are even more sticky, than this one.
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Hope you enjoed. Seeya next video