I have been doing synthesis of PNIPAAM in different molecular weight. The precipitation is really a tough problem. Because I couldn't separate the monomer from the polymer clearly with ethyl ether alone or petroleum ether alone or both of them in the ratio of 1:1. I can always see the peak of NIPAAM monomer in HNMR even after 3 times of precipitation. I want to know how other are doing this and can anyone give me some advice? Thanks a lot!
Dear Chao,
Yes, reprecipitation of a polymer might be tedious and difficult. You should find a good solvent for the monomer which is a bad solvent for the polymer.
Nevertheless, did you try to heat up above the LCST of polyNIPAAM? You know... above this temperature, the polymer collapses and can be centrifuged, but the monomer remains highly soluble. Repeat it several times and let me know.
SALUT!
Tony
Dear Chao,
If PNIPAAm is obtained by aqueous redox polymerization, you can precipitate the PNIPAAm in the same amount of water due to the cononsolvent behavior of the methanol/water. Additionally, resulting polymer could be purified by dissolution in chloroform and further precipitation in an excess of hexane.
Regards,
Erlantz.
Fully agree with Erlantz,
From a good solvent to a bad solvent mixture but keeping the monomer soluble.
SALUT!
Tony
Dear Chao,
Previous advice from Antony is the most reliable and simple in my opinion. You can use filtering Instead of centrifugation, to wash the polymer on the filter with hot water, and then rinse with cold water.
You can simply remove the monomer residual in a vacuum, because it is a quite volatile substance.
Yakov
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