A variety of cross-linking agents can be used such as: 1,4-phenylene-bis-acrylamide; N,N'-bis(acryloyl)cystamine; 2-(methacryloylamino)ethyl 2-methyl acrylate , etc.

It depends on the polymerization medium (the solubility issue). However, to match the reactivity ratios of functional monomers and to ensure smooth incorporation of the comonomers, the reactivity ratio of the cross-linker should ideally also be matched to that of the functional monomer(s). This roughly means that the crosslinker should have a similar structure to the monomer.

Well, it depends if 1) you just want replacement reagent while maintaining the same functional group (acrylamide) or does not matter, 2) If you want replace change the functional group... Anyway, if you are making hydrogels, for example, there are many compounds such as glutaraldehyde can be used as cross-linking agent. Some other crosslinking compounds are formaldehyde, epoxy compounds, dialdehyde... Anyway, I can suggest ethylene glycol diacrylate or PEG diacrylate.

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