SPTES polymers have been successfully synthesized by direct polymerization using tetramethylene sulfone as the solvent. The chemical structures of the SPTES polymers are confirmed by FT-IR ahd NMR spectroscopy. The thermal stability is characterized by TGA, and the results show that the sulfonated groups on the polymer backbone are stable up to 300 degrees C. The measured proton conductivity reaches values above 300 mS . cm(-1) at 65 degrees C and 85% relative humidity. Tough, ductile, free-standing membranes have been fabricated by solution casting from N,N-dimethylacetamide, which indicates that the SPTES polymers have excellent mernbrane-forming capability and mechanical property. The mono-functional monomers are introduced into the polymerization to end-cap the SPTES polymers. The end-capping groups are effective in improving water, resistance, oxidative stability, and retaining the proton conductivity.