Question

Why is polyacrylamide insoluble in acetone and ethyl acetate?

Answer 1

Polyacrylamide is soluble in cold water and morpholine (C4H9NO). It is insoluble in pretty much everything else. You have to be careful, some materials marked "polyacrylamide" are actually compolymers, with 97-99% acrylamide repeat units, and the balance something else (usually an acrylic or multifunctional monomer). In this case, it will only form a gel.

Polyacrylamide is ususally a huge molecular weight material, so it will take a long time to dissolve. Perhaps your solubility test in water might have passed if you had given it an hour or two, at least, to go into solution. Heating will not help dissolve it; in fact, polyacrylamide will crash out of water solution upon heating.