Soxhlet extraction may be your best option for removing monomer

It would be good to have more details about your gel. If it is a hydrogel, it may be enough to place it, similar to a dialysis bag, into a large beaker with water or aqueous buffer solution, at slow magnetic stirring, to follow leakage of the monomer by its UV absorbance and to change water from time to time.

Thanks to Dr Andrew really i havnt think of extraction of residual monomer in that angle. Generally we do soxhlet extraction for extraction of pesticide residue from soil or grain sample. really need to check it.

Dr Ivanov thank you for your valuable suggestion. Yes i was talking about hydrogel. But i have some question regarding it because the experiment you are suggesting is more like checking of release of residual monomer from hydrogel sample which may of long procedure taking more than two days depending on the networking characteristics of hydrogel. I need some method which is less time taking and can extract all the residual monomer at one time.

To make it a bit faster you may consider freeze-drying, of course if your monomer is volatile. Note, however, that freeze drying may affect the gel pore structure. I would go to the dialysis-like method suggested before because it gives you a way to measure the washed out quantity: in case if you need to confirm that the monomer has been actually removed.

Dr Ivanov what do you think about solvent replacement method for extraction of residual monomer?

Applicability of solvent replacement (and other methods) depends on your goals. This was the reason why I wished to have more details (perhaps, some other readers too). Just conceive that people who answer your question do not have idea of the shape, size, exact chemistry and the purpose of your gel, whether you need it intact or it can be destroyed ,etc. I was accidentally right presuming you have a hydrogel. If you have your gel in small pieces or you do not mind to destroy it into small pieces, then solvent exchange (for example in a Soxlet, as Andrew Lowe suggested, may be fine.

Depending on the nature of your application, you could perhaps even look at the treatment of the hydrogel with ionising radiation in order to graft the monomer onto the polymer. Relatively low irradiation dose should be considered as most acrylic polymers tend to degrade under irradiation.

I agree with Dr Ivanov method - the dialysis like method. If you have large gel, you may place it in some netting/clothing and let it completely immersed in water. Change the water every day and follow the concentration by using UV-Vis until there is no residue. The most you can do to speed the process up is by using stirrer, apply heat, larger volume of water and maybe other solvent that can dissolve acrylic monomer better than water.

I agree with Dr Ivanov and Dr Hamzah. The extraction of residual monomer is a diffusion process. Therefore, we should make one dimension of the gel small and change the water frequently (to enlarge the concentration gradient).

just a simple remark concerning the soxhlet extraction. The selection of the extraction solvent must be donne with great accuracy for two main reasons:

- the problem of residual solvent, so the solvent must have a good affinity to the monomer and a very poor one to the matix (gel).

- one should be aware about the possible change in the morphology of the gel since the twin effect of the solvent and heat may surely induce or impart physical changes in the morphology, of cource if the morphology is among those important operating factors of your system.