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Topic: Polymerization reaction mixture becomes too viscous to proceed?  (Read 511 times)

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Offline PSbP2VP/NMP+PtCl62-

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Polymerization reaction mixture becomes too viscous to proceed?
« on: February 09, 2021, 01:48:01 PM »
I am trying to synthesize 3 g of a 1:1 random copolymer of styrene and methyl methacrylate using nitroxide mediated controlled radical polymerization. The recipe that I am following involves adding S, MMA, and Initiator (2-phenyl-2-TEMPO-ethanol) alongwith a small amount of solvent (toluene) to a schlenk flask, remove dissolved oxygen with three freeze-pump-thaw cycles, and then let the polymerization happen at 125C for 72h. However, after only 17 hours, the reaction mixture has decreased substantially in volume and become so viscous and dry that even the stirbar isn't moving! Is this something that happens to polymerization reactions, and is there a way to get around it?

Online rolnor

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #1 on: February 09, 2021, 04:25:52 PM »
Methylmetacrylate has bp 101°C?

Offline PSbP2VP/NMP+PtCl62-

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #2 on: February 10, 2021, 03:38:32 AM »
Yeah but it's a sealed vessel. It's not going to go away.

Online rolnor

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #3 on: February 10, 2021, 04:44:16 AM »
Could it be a leak? How do you explain the decreased volume?

Offline Enthalpy

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #4 on: March 03, 2021, 05:54:43 AM »
How well do you protect MMA against light?

Offline PSbP2VP/NMP+PtCl62-

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #5 on: March 03, 2021, 05:10:55 PM »
You guys, I'm sorry for not checking back in here for so many days. It turns out that a lot of the monomer/solvent were getting absorbed into the red rubber septa that I used to seal the flasks! I purchased some septum inlet adapters to replace the rubber septa, and the volume doesn't change and I am getting excellent yields.

Everyone uses these NR septa in our lab but most of them do reactions in much larger batches so I suppose the effect isn't as drastic for them as it was for me.

In any case, thanks a lot for thinking about the problem and for your inputs!

Offline PSbP2VP/NMP+PtCl62-

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #6 on: March 03, 2021, 05:15:26 PM »
How well do you protect MMA against light?

This is an interesting point. I actually don't do anything to protect it against light. My understanding was that because I'm making a random copolymer and not e.g. alternating/gradient copolymers, a small degree of autopolymerization in visible light wouldn't make a big difference.

Offline wildfyr

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #7 on: March 03, 2021, 10:41:18 PM »
Don't worry about ambient light with this polymerization. MMA absorbs the fluorescent light in the room very poorly, and the TEMPO derivative that gives you the "living" polymerization characteristics is what matters most.

If you left the reaction for weeks maybe auto photopolymerization would matter.

As a subtlety here, there is some reaction gradient with styrene and MMA in a nitroxide mediated polymerization like this. I'd have to go look it up, but I think NMP is "happiest" with methacrylates, followed by styrenics, followed by acrylates. So in the start of the reaction the polymers will be enriched with methacrylate, and as it gets used up styrene will be more enriched. Its been many years since I ran the reaction, so maybe its vice versa. Anyways, shouldn't matter much for you.

Offline PSbP2VP/NMP+PtCl62-

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #8 on: March 07, 2021, 09:41:04 PM »
Thanks for your thoughts, wildfyr!

Offline Enthalpy

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #9 on: March 08, 2021, 06:21:06 PM »
Don't worry about ambient light with this polymerization. [...]

I have no opinion about the exact setup described here. But I can testify that MMA fully hardens in <10min under fluorescent lamps for having used that. So in 72h, I'd expect strong competition from induction by light, even if light isn't as concentrated as what I used.

I had one long tubular lamp every 0.1m at 0.2m distance in my setup. One lamp every 1.5m at 3m distance would do the same hardening in 15*10min=2.5h. Fewer lamps acting over 72h must polymerize MMA very efficiently.

Offline wildfyr

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #10 on: March 10, 2021, 09:34:35 PM »
"But I can testify that MMA fully hardens in <10min under fluorescent lamps." Normal office white light lamps???

What?? With no photoinitiator? I'm currently employed as a UV radiation curing coatings chemist, and literally worked with MMA this morning. So you are going to have to provide some more information. Heck in 10 minutes a thin coating of MMA will evaporate noticeably!

Even acrylate oligomers (which we use more typically, and are significantly more reactive than methacrylates) need to be blasted with hundreds of mJ/cm2 of UV light with a photoinitiator to polymerize appreciably. Typically its done in a couple seconds, but still... the  sub 250 nm UV in typical fluorescent lamps is tiny. MMA absorbs below 260 nm. And without a photoinitiator!? I literally have glass vials full of acrylates without a PI sitting on my bench for weeks still liquid.

Enthalpy, did you remove the phosphor filter from the lamps? That would make more sense, as much more UV would be impinging on your MMA in that case.

With the phosphor on, the spectrum is virtually UV-less https://en.wikipedia.org/wiki/Fluorescent_lamp#/media/File:Fluorescent_lighting_spectrum_peaks_labeled_with_colored_peaks_added.png

Offline Enthalpy

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Re: Polymerization reaction mixture becomes too viscous to proceed?
« Reply #11 on: March 11, 2021, 08:24:14 PM »
Hey, you believe what you want!

I used completely standard fluorescent tubes. They emit some UV, the fraction that goes unabsorbed through the phospors.

And I just followed the recommendations by the MMA provider, it worked perfectly. I didn't check any absorption spectra or whatever. I just testify the MMA polymerizes in <10min under these conditions.

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