I am working on polymerizing monomers similar to lactic acid, each containing one carboxylic acid and one alcohol group, through a polycondensation technique. Despite using vacuum conditions during polymerization and employing titanium butoxide as a catalyst at high temperatures (180°C), I am encountering difficulties in achieving high molecular weight polymers. Specifically, the molecular weight of the resulting polymer reaches only about 20 kDa, whereas my target is around 40 kDa.
Initially, I conducted the reaction for 16 hours at 180°C. Following this, I increased the temperature to 230°C, and after one hour, I applied a vacuum for 4 h to enhance the molecular weight. This polymerization process is being carried out in bulk.
If I were to use a solvent, which solvent should I use and at what temperature?
Please give a suggestion.
Dear Md SHAFI Alam ,
This might not address your problem, but when doing this type of polymerization, normally the reaction is chemically controlled at the beginning, but since the viscosity of the reaction media is constantly increasing, at some point it becomes diffusion controlled. To overcome this and achieve higher molecular weights, the first option is to increase temperature. I think you already tried this and the results are not that successful. To that approach, I would suggest adding some solvent to decrease the viscosity of the reaction media so the molecules can keep reacting. Also, temperature steps might be quite useful, instead of setting a constant temperature through the whole reaction.
Hope this helps!
Agustin Forchetti Casarino
Initially, I conducted the reaction for 16 hours at 180°C. Following this, I increased the temperature to 230°C, and after one hour, I applied a vacuum for 4 h to enhance the molecular weight. This polymerization process is being carried out in bulk.
If I were to use a solvent, which solvent should I use and at what temperature?
Dear Md SHAFI Alam ,
When using the solvent, just keep in mind about its boiling point. According to the process you are commenting, solvent might be used during your 180C and your 230C stages, at ambient pressure. This means you would need a solvent with a very high boiling point (more than 230C). When you apply vacuum, the solvent will boil at a lower temperature, so in your last stage of the reaction it will be eliminated.
If it is hard to find a solvent with a boiling point above 230C, just use solvent during your 180C stage (by using a solvent with a boiling point above 180C). Then, when increasing temperature, the solvent will be eliminated. DO NOT CLOSE YOUR SYSTEM, BECAUSE THE SOLVENT NEEDS TO COME OUT. If you close it, it will increase the pressure inside and that can be dangerous.
Just a comment: I am not aware of the synthesis of PLA from polylactic acid at all, but I found 180C a very high temperature for a chemical reaction. Maybe checking a bit more about this might give you some ideas on how to operate.
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