Dear Mohosin Rana, I think the following reasons are behind this problem.

- may be this conditions favor the cage effect, since with AIBN generally the polymerization temperature of 60°C is enough. Also AIBN concentration is to be checked.

- may be N2 is not dry and pure enough. Purging for a time between 20-30 min is sufficient.

My Regards

Dear Abdelkader BOUAZIZ, thank you so much for the answer.

- I've used 0.04 g of AIBN in this case. Moreover,I also tried with the polymerization temperature 60oC and got no polymers.

- The N2 cylinder that I am using is the same one that I used earlier to do the polymerization with different feed composition (high cross-linker density) and it worked. It also made me more confused. Because, I am using same experimental settings, just changed the cross-linking density and now facing trouble to get polymers from polymerization with low cross-linker density (1 mol%).

Hope this will help you to give some solutions to overcome this problem.

Thanks again.

For sure it is the dissolved O2 problem you entangled with. So, I recommend to properly degas the solution with N2 gas, and then seal the solution under the inert atmosphere. The free space of the reaction vessel should be as small as possible.

To do so, you can use a screw cap vial with a rubber septum fixed on the cap. Insert a large needle beneath the solution through the septum for feeding the vial with N2 gas, and use another small needle as an outlet (similar to the attached figure). Degas the solution for about 10 min. If the solvent is volatile, put the vial in an ice bath while degassing.

Dear Ali Nematollahzadeh , thank you so much for the reply. I was also considering this issue as a reason. But I am confused because your instruction is bit similar to my setup I think. I've attached the illustration of my setup for your kind concern. Please note that, last 6 months I am working with polymer synthesis in this way and I got polymers every time. But once I reduced the cross-linker concentration, I started to face this problem. I purge the solvent at 18oC with N2 for 30 min before adding the feed components in the solution. I used to add 100 ml solvent in 250 ml sized flask with 2 g monomer and 10 mol% crosslinker. But this time I changed the crosslinker to 1 mol%. The three possible reasons are in my mind, i) dissolved oxygen, ii) inhibitors present in the reaction, and iii) inability of AIBN to initiate the reaction. For first issue, as I said, I double checked the setup, although this time I am using new N2 cylinder (99% purity). For the second issue, I used freshly recrystallized both monomer and AIBN. The only issue from my side is now AIBN. I am not sure whether that one is a major issue or not. Is there any other way I can crosscheck these three issues? Please kindly let me know if you have any suggestions. Thank you again.

Dear all, bubbling is passing N2 through the solution via a glass tube. It is the dissolved O2 that inhibits polymerization. The O2 presents above the solution is less harmful since it needs a certain time to be dissolved first after that it may reacts with free radicals. So, if this not an error in drawing the setup, you are not purging the reactants solution, and this may be the reasons why no polymerization took place. My Regards

Already we have experienced the same problem in our Lab.

Employing the set-up similar to that you attached herewith but a bit elegant, we tried but it didn't work! When we changed the initiator from AIBN to APS or BPO, it worked. We concluded that AIBN is more sensitive to the O2.

When we used a smaller vessel (150 mL flask for 110 mL solution with AIBN) with careful degassing and sealing the flask, it worked again. But the same volume of the reaction solution didn't work in a 250 mL flask! Overall, the reaction was not reproducible.

To see a proper setup for O2 sensitive polymerization reaction please see the following link

https://www.chemistryviews.org/details/education/4360441/Tips_and_Tricks_for_the_Lab_Air-Sensitive_Techniques_3.html

Finally, we decided to use smaller reaction vessels with as low possible as free space on top of the solution, and of course, with careful sealing of the necks.

As it is difficult to seal glass flasks, especially the outlet of the condenser, we use a glass vial with escrow cap with a hole in the middle of the cap. The cap does not let the septum to burst out (like a Penicillin vial with septum and cap). First, we put a rubber septum on the vial and then cap it. As I explained in the previous post, we use 2 needles for the degassing. After finishing the degassing, first we remove the small needles, then the large one. In this case there is no need for condenser and sophisticated glassware.

It is more easy to use a glass vial with the rubber septum attached herewith, with no need for escrow cap.

Dear all, if you have polymerization tubes similar to those used in a Schenk setup, it is more efficient to use freeze-thaw cycling to eliminate O2 instead of N2 purging. My Regards

Dear Abdelkader BOUAZIZ

I agree with you. Schlenk tube is a good choice for freeze-thaw and then closing the stopcock under N2 blanket.

This is the reaction vessel we used with 100% reprehensibility.

Dear Ali Nematollahzadeh & Abdelkader BOUAZIZ , Thank you so much for the elaborate explanation of the reason. These illustrative images are also very helpful to understand the problem and the way to solve it. I will do degassing more promptly according to your suggestions. Hopefully, it will work. Thank you once again for your suggestions and tips.

Mohosin Rana I would be grateful if you could let me know the outcome.

Dear Ali Nematollahzadeh , yeah, sure. I will definitely let you know the update...thank you again...

Dear Ali Nematollahzadeh

Thanks for helping me out. Finally, It worked! I am really grateful to you for your assistance.

Excellent! How was it resolved?