RareEarth
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Unable to get styrene to polymerize...
I'm attempting to coat glass beads with styrene monomer + 5% divinylbenzene for crosslinking, and I have not had any success getting the
polymerization reaction to occur.
The glass beads are being stirred in a kitchen-stand mixer. I used Methyl Ethyl Ketone Peroxide (MEKP, also contains some H2O2, liquid resin hardener)
from the hardware store, and a cobalt salt as the initiator for the MEKP. MEKP is used in conjunction with cobalt salts to initiate radical reactions
for hardening fiberglass resins.
So, with the beads stirring with the styrene + DVB, I added about 2% by weight of MEKP and Cobalt salt (more than enough to get the reaction going). I
thought the reaction started to heat it, signifying a reaction, but it may have been heat generated from the mechanical friction of the stirrer.
I let this go overnight and in the morning all the liquid was gone, and the beads weighed almost exactly the same, when they should have weighed 200g
more. So, all the styrene and DVB evaporated (and no there is no way for me to seal off the stirrer to prevent this).
I don't understand, what could have gone wrong? This is actually the second attempt I have made at this process, the first one I utilized AIBN + UV
light. That one failed and I had just assumed my AIBN was inactive due to being left in a hot storage unit for months. I didn't think this second
attempt would fail. How can such an easy reaction go wrong?
The only thing I could think of is that my styrene monomer is bunk somehow, but I'm not sure how. Can anyone perhaps suggest where I might find
styrene monomer locally?
[Edited on 24-6-2015 by RareEarth]
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Ozone
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1. Your monomer(s) may be stabilized with TBHQ or the like. Pass it through chelex resin or distill prior to use.
2. Avoid air if possible.
3. Try heat. AIBN has an initiation half life of about 10 Hr at 80 °C. Of course, you will need a sealed vessel.
4. Your UV may not be sufficiently strong at the particular wavelength you need (or is filtered out by glass, plastic, etc). You may want to look up
the emission spectrum and wattage/flux (distance is key, here) and plan accordingly. Or, try an appropriate photosensitizer.
5. Benzoyl peroxide/catalyst should just go (hardener for Bondo, for example). Again, heat makes it go faster.
6. Have you tried a simple resin-casting kit (styrene-BPO/cat)?
7. For large bulk polymerizations, beware of gel-effect (Trommsdorff), particularly if heated.
8. How do you propose that the cross-linked material will coat the beads? I suspect you will get a solid block of polymer with the beads cast inside.
O3
[Edited on 24-6-2015 by Ozone]
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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RareEarth
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1) The DVB did have a stabilizer with it, but at very small quantities. I used excess initiator to combat this so this should not matter. The styrene
itself was from an online shop that sells it specifically for curable polymer-coatings.
2) I didn't think air would be much of a problem since many of these products and their applications are designed to be cured in open air.
3) It's difficult to heat since it is being mixed in stand mixer, and I have no way to contain/condense the vapors. Heat would be ideal, but not
possible in this case, and honestly shouldn't be necessary. MEKP/Co is often used for very rapid room temperature curing.
4) The UV was from a "reptile UV bulb" and was very close to the beads. I honestly just think my AIBN was inactive since it was in a storage unit for
8 months which would sometimes be at 100f for many days straight. Poor storage on my part.
5) The MEKP that I used was bondo brand, though I plan on ordering a bottle of it. The bondo fiberglass resins usually contain cobalt in the resin
which reacts with the MEKP when it is mixed.
6) Do they sell polystyrene resin casting kits anywhere locally? I was just at an arts and craft store and didn't see any.
7)
8) Well initially I was adding a slight bit of styrene at a time. Maybe 1/10th of the volume of the beads. As a measure, I also added food coloring to
see if the beads were being coated properly. Sure enough, after enough stirring, the beads were entirely coated. The mechanical stirring would have
been strong enough to prevent any sticking of the beads together. As long as a pool of liquid was prevented, the beads should not all stick together
as a single mass.
Regardless of all this, the MEKP and cobalt should have done the trick. I have seen guides on using MEKP polyester/styrene resin kits and they all say
you have to work with it very quickly because it is fast acting (sometimes on the scale of less than 10 minutes).
I'm in a bit of a predicament because I can't heat this in the current vessel because of no reflux, and I can't use an actual vessel because to my
knowledge there is no easy to mix the beads amongst themselves completely. The mixing shaft would need to scrape all sides of the vessel.
Do you have any other suggestions to how I might acquire some cross-linked polystyrene beads/pellets? All the ones online are either non-crosslinked,
super expensive (5g / $100), or functionalized (ion exchange resins), and despite much searching I cannot figure out how to directly make reasonably
sized polystyrene beads from monomer.
[Edited on 24-6-2015 by RareEarth]
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Ozone
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Suspension or emulsion polymerization, probably with either BPO (organic phase) or REDOX initiation (Fe/persulfate, for example) would give beads. The
size would relative to the shear applied during the polymerization and quantity of surfactant.
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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Dr.Bob
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If the UV lamp light is passing through the glass or plastic container walls, the UV component will be filtered out a lot. The light needs to either
be over the open container, or the container needs to be UV transparent material, such as quartz. That is why photochemistry is such a pain, except
in a shallow glass baking dish on the rooftop...
Chem with Polymer Labs, they specialize in cross linked polystyrene, as well as AAPPTec, Advanced CHemtech, and almost any peptide chemistry company.
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zed
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Bondo brand? Red Paste in a tube?
I used to cast a lot of Styrene. Used a clear, liquid form of MEK Peroxide. Worked, but not as well as you might think. Remained tacky, almost
indefinitely. Used to finish the hardening by boiling the molded castings in H2O.
How big are those glass beads? Some reason you can't just dip 'em in molten poly-styrene, or dip 'em in a styrene solution.....?
So, just how big do your poly-styrene beads need to be?
Styrene ain't hard to acquire, if it turns out there is a problem with the styrene you are currently using. You can always de-polymerize some
existant poly-styrene, via destructive distillation(AKA pyrolysis). Old clear, audio cassette cases seem like a likely source. Not much additive.
Also, keeping in mind that Poly-styrene is a thermo-plastic material, it might be possible to cast beads from a melt. Or, let molten drops, fall into
water. Depending on size required.
[Edited on 26-6-2015 by zed]
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Ozone
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Unfortunately, the polymer will be not thermoplastic after it is cross-linked with DVB.
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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zed
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Had a friend who experienced problems producing polymer beads. Turned out it was actually a case of industrial espionage. A Mole, had contaminated a
critical reagent, to insure failure.
As I recall, Butylamine was the culprit. So it goes. As hard as Chemistry is, sometimes folks work to make it harder.
So, how big do those beads need to be?
[Edited on 27-6-2015 by zed]
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