It may be cross linking in the oven at 50˚C. try drying at room temperature.

Dear all, I think the molecular weight is too high, may be above 10 millions (g/mol). I encountered similar problem with homopolymers of polyacrylamide. My Regards

We have faced similar issue when polymerization of AAM. However, the precipitate was dissolved under continuous mixing and heating.

Hi;

I totally agree with Pr. Peter Bedwell, the insolubility can be the result of a cross-linking of the polymer during the drying in the oven. Please check the following document.

With my best regards

I think, molecular weight and polydispersity are too high. You can reduce polymerization reaction time. When drying in vacuum oven, you can decrease the temperature below 40 °C.

You can use mixed solvent, first miscible organic polar solvent to dissolve it and then add water as 2nd solvent.

There is possibility to cross-link between acrylamide and sulfonic acid groups. But if the product is purified well, then the possibility for cross-linking will be very low. Try to remove solvent in room condition and then dry in vacuum oven.

One way to avoid crosslinking is to neutralize the AMPS units before drying with Na2CO3 or another inorganic base. The sodium or potassium salt of the sulfonic acid would be less active in promoting the crosslinking reaction. In my opinion the crosslinking is caused be reaction of the amides to imides.

----CO-NH2 + H2N-CO----- -> ---CO-NH-CO---- (acid catalysed)

Further it would be advisable to regulate the molecular weight of the copolymer with a thiol like mercaptoethanol.