I am conducting free radical polymerization with the following conditions:
- Initiator: AIBN
- Solvent: DMF
- Monomer: MMA (5 g)
- Initiator Amount: AIBN (0.04 g)
- Solvent Volume: DMF (20 mL)
- Reaction Temperature: 70°C
- Reaction Time: 6 hours
- Atmosphere: Nitrogen (N₂)
- Setup: Condenser used
However, instead of obtaining a powdered polymer, I am getting a gel-like or highly viscous polymer. Please suggest what could be the reason.
Thank you
Dear Ismail Khan ,
Are you evaporating the solvent after your polymerization? If you try to eliminate the DMF from the reaction after the MMA is polymerized, you might be able to obtain a powder as you mention.
Maybe the high viscosity/gel aspect might be due to a plasticizing effect of DMF that is trapped in the polymer matrix.
Best of luck!
All of the conditions for your reaction seem to be proper.
But in the case of the use of DMF as solvent, you have both the monomer, MMA, and the resulting polymer, PMMA, soluble. So, what happens is your dissolved monomer is polymerizing into a polymer which becomes dissolved in the solvent as well.
You are probably reaching very high conversion, and therefore, large molar mass for your polymer.
In order to isolate your polymer you can either add a non-solvent, such as ethanol, or vacuum dry your reaction medium to eliminate the solvent. I also suggest reducing the reaction time.
Hi, Thank you for the response. I aim to obtain a high molecular weight polymer, but my current sample shows multiple GPC peaks, with a major peak at MW = 2400 Da, suggesting incomplete chain growth and possibly causing the jelly-like polymer. YES, After polymerization, I precipitate PMMA using cold methanol as an anti-solvent and dry the sample overnight in a vacuum oven. How can I improve polymer chain growth to get a high molecular weight? Should I change the solvent to avoid the plasticizing effect? Joao Arthur Batalha Agustin Forchetti Casarino
You could try bulk polymerization, by not using a solvent. You just need to add the radical initiator to the MMA and apply temperature.
It usually yields higher molar masses. On the other hand, it also yields greater polydispersity.
However, you need to be very careful in controlling your reaction, especially temperature, or else you could come across the gel effect, when molar mass grows very fast and limitless.
prof. Joao Arthur Batalha thank you for the response. My project scope is not to use bulk polymerization and use any solvent and do free radical polymerization and get a high molecular weight PMMA. With solvent, I have more control over the reaction condition, and also later on I can mix different materials and see the effect of those. Could you please share if there is any literature on MMA-FREE RADICAL POLYMERIZATION USING AIBN IN A SOLVENT? I am unable to find it .Thank you
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