Synthesis of Neopentyl Styrene Sulfonate

Jerry Gilligan, Vassar College ’11 and Prof. Sarjit Kaur

Polymer Electrolyte Membranes (PEMs) are proton conducting materials that are being developed for a variety of applications including fuel cells. PEMs are typically sulfonated polymers that show high proton conductivity, are thermally stable, and can form intact membranes. While Dupont’s Nafion PEM meets these basic requirements, it is expensive, shows permeability to methanol (a possible fuel), and cannot be used above 80°C. Thus there is interest to develop hydrocarbon based PEMs that also show high proton conductivity. The focus of this project is to develop a sulfonated, nanoporous triblock copolymer with a controlled morphology that can improve proton conductivity through better conduction paths, and a triblock copolymer, poly(lactide-sulfonated styrene-styrene) was selected to test this concept. The PLA block was previously synthesized using ring-opening polymerization of lactide using a bifunctional initiator. Previous attempts to add the sulfonated styrene block directly using styrene sulfonic acid were unsuccessful, possibly related to the presence of the free sulfonic acid group. In order to overcome this problem, styrene sulfonic acid was protected using a neopentyl group. Styrene sulfonic acid was first reacted with thionyl chloride in DMF to give styrene sulfonyl chloride. This molecule was then reacted with neopentyl alcohol to obtain neopentyl styrene sulfonate. Both reactions initially gave low yields and were optimized to improve yields. Future work will focus on adding the neopentyl sulfonated styrene to the PLA block containing a nitroxide initiating end group.