Preparation of poly(styrenesulfonic acid) grafted Nafion with a Nafion-initiated atom transfer radical polymerization for proton exchange membranes

Abstract

This work reports the synthesis of a poly(styrenesulfonic acid)-grafted Nafion (Nafion-g-PSSA) copolymer through atom transfer radical polymerization (ATRP) using Nafion chains as a macroinitiator. The C–F linkages of the –CF– groups and –CF₂–SO₃H groups serve as the initiating sites for the ATRP of the employed styrenic monomer. The PSSA chains further enhance the hydrophilic–hydrophobic microphase separation in the Nafion-g-PSSA based membrane, demonstrating relatively large ionic cluster domains and small distances between the hydrophilic and hydrophobic domains compared to the neat Nafion based membrane. Consequently, Nafion-g-PSSA is an effective additive for the fabrication of Nafion-based proton exchange membranes. With an optimum fraction of 15 wt% Nafion-g-PSSA, the modified Nafion membrane exhibits a proton conductivity of about 97 mS cm⁻¹ (95 °C, RH = 100%), which is larger than the values measured on the recast neat Nafion membrane (53 mS cm⁻¹) and a commercial Nafion 212 membrane (88 mS cm⁻¹). The Nafion-initiated ATRP is effective for preparation of Nafion derivative materials for proton exchange membranes.