Hi, guys! Today I am arriving with a new question. I am facing a problem while purifying a polymer. Then I doubt whether the polymer is getting purified! After synthesizing the polymer, I am dissolving the polymer in the minimal volume of solvent, and then I am precipitating it in the excess amount of non-solvent followed by drying to collect the final product.
Here my question is that is the unreacted monomer getting out of the polymeric part? If yes, then how? Because I am drying the material with containing both solvent part and non-solvent part.
Hi,
You need to separate the precipitated polymer from the liquid, for example simply by filtration. The non-reacted monomer should be mostly dissolved in the liquid (antisolvent for the polymer but solvent for the monomer). Then you need the cycle re-dissolution, precipitation, filtration - typically 3 times.
Best wishes
Hi..
hopefully the polymer will precipitate out, and the monomer will remain in solvent due to comparatively more solubility.
Please, follow the recommendations of Daniel Crespy. Besides, you need not limit the amount of solvent too much. For an effective polymer purification, its solution should not be viscous !!!! AND it should be added into non-solvent drop-by-drop under intensive stirring !!! After primary separation by filtration or upon sedimentation of the precipitated polymer, wash it a few times with the non-solvent to remove soluble residues as much as possible.
Best wishes, JV
The normal method for radio tracer work is : dissolve the polymer in a solvent then precipitate it in a non solvent. The polymer is then dried and the process repeated as many times as required. For example polystyrene is soluble in benzene or toluene. So dissolve about 1g in 20 ml of toluene and precipitate it in 400ml methanol, filter and dry the polymer under vacuum at 40C. Repeat the process several times if necessary . In the case of C14 labelled AZBN,this can be mixed with an inactive polystyrene and the C14 activity checked after each purification . Hence the number of purification can be decided.
In the case of polyvinyl acetate benzene was used as solvent and n-heptane non solvent. For polyacrylonitrile DMF was the solvent and methanol the non solvent.
So you need a sensitive method for monomer detection to test your metod.
Daniel Crespy sir thanks for your answer. But can you mention what filtration technique shall I apply to for separating the precipitate from monomer?
If you are getting large solid particles, you can do vacuum filtration or gravitational filtration on a Whatman 1 filter paper. If the particles are small/fine use gravitational filtration on. Whatman 5. Your product stays on the paper. If the particles are extremely fine use centrifugation instead and decant the solvent carefully. The product is at the bottom. A common occurrence is that you can get the product as a gel. That sticks to the walls of the collecting vessel and if its transparent you wont see it but only when you decant the supernatant.. Whats the polymer by the way?
I agree with others. Sometimes you need to do this solution and precipitation steps for few times. Make sure while precipitating your polymer in non-solvent, stir it for a while. You can then centrifuge the solid part or filter it by filter paper. Wash the solid obtained again with the non-solvent (for several times) so that it takes away the monomer adhered to the solid. Then run an NMR to check the presence of monomer.
Thanks, Parijat da! Thanks to everyone for their ideas. I'll try my best with them to make the polymer purified.
Purification by repeated dissolution in solvent and precipitation in nonsolvent is general method. You need to select solvent/nonsolvent combination, so that the polymer is precipitated and monomer, catalyst remain in solvent/nonsolvent mixture. At times you have to use solvent combination. Even hot solvent is used sometimes. If the polymer solution is concentrated, it may retain monomer/catalyst adsorbed. Very dilute solution of polymer is the answer. 2-3 reprecipitations will give the desired purification. For a tenacious monomer, keep the polymer in a good solvent and leave for 24-48 h.
you should not assume purification, nor having doubts. You need to have some basic analytics measuring polymer purity and unreacted monomer concentration.
Thank you, Asit Baran Samui sir for your kind response. Can you kindly give a kind explanation whether the remaining monomer gets devoid of the resultant polymer via repeated precipitation? If yes then how? Because I am doing the precipitation repeatedly in the same beaker or a petri dish followed by drying.
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