Certain polythioether polymers are presented, as well as compositions which are radiation curable to polythioether polymers and seals and sealants comprising same. The compositions radiation curable to polythioether polymers include those comprising: a) at least one dithiol monomer; b) at least one diene monomer; c) at least one multifunctional monomer having at least three ethenyl groups; and d) at least one photoinitiator. In another aspect, the compositions radiation curable to polythioether polymers include those comprising: f) at least one dithiol monomer; g) at least one diene monomer; h) at least one multifunctional monomer having at least three thiol groups; and i) at least one photoinitiator. In another aspect, the compositions radiation curable to poly-thioether polymers include those comprising: k) at least one thiol terminated polythioether polymer; l) at least one multifunctional monomer having at least three ethenyl groups; and m) at least one photoinitiator.