Novel sulfonated block copolymer containing pendant alkylsulfonic acids: Syntheses, unique morphologies, and applications in proton exchange membrane

In this article, we report the syntheses and charac- terizations of a series of novel block polyelectrolytes, poly(sty- rene-block-sulfonated hydroxystyrene) (PS-b-sPHS), containing pendant sulfonic acid groups attached to the backbone via propyl spacers in the sPHS domain. PS-b-sPHS with various compositions were synthesized via anionic polymerization and the following analogous chemistry to achieve accurate control of molecular weight (Mw), narrow polydispersity and high degree of sulfonation. Proton exchange membranes (PEMs) were prepared from PS-b-sPHS with sulfonic acids in either po- tassium salts or tetra-alkylammonium salts via solvent casting and following treatments. Some unique morphologies, such as hallow channels and lamellar arrangement of strings of beads, were observed as a consequence of equilibrium between microphase separation and columbic interactions between pol- yelectrolytes. The transportation properties were found to closely relate to the morphologies of the PEMs. The combina- tion of microphase separation of block polyelectrolytes and freedom of movement of pendent alkylsulfonic acids was dem- onstrated to effectively enhance the proton transport and sup- press the methanol crossover for the PEMs, leading to the selectivity higher than Nafion 117 by five times at most. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2325-2338, 2011