Synthesis and characterization of novel phosphonated and sulfonated poly(styrene-isobutylene-styrene) for fuel cell and protective clothing applications
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A novel aromatic block–graft copolymer of sulfonated poly(styrene–isobutylene–styrene)‐graft‐poly(vinyl phosphonic acid) (SIBS‐g‐PVPA SO3H) was synthetized for direct methanol fuel cell (DMFC) and chemical and biological protective clothing (CBPC) applications. The polystyrene (PS) blocks of SIBS were chloromethylated via a Friedel–Crafts reaction to obtain the macroinitiator SIBS‐CH2Cl. Atom transfer radical polymerization (ATRP) was performed to graft VPA to the chloromethylated groups of the macroinitiator and yield SIBS‐g‐PVPA, which was subsequently sulfonated using acetyl sulfate as the sulfonating agent. After each functionalization step, a membrane was prepared by using the solvent casting technique. The final membrane was composed of triblock SIBS as the backbone, PVPA grafts attached to the chloromethylated PS end blocks and sulfonic groups in the non‐chloromethylated PS units. A comprehensive materials characterization study (e.g., GPC, FTIR, TGA, EA) was performed to confirm proper functionalization of each material. Unique ionic interactions (i.e., crosslinking via formation of sulfonate–phosphonium complexes) arose between the phosphonic and sulfonic groups (i.e., PO3H2 and SO3H, respectively) that enhanced the water absorption capabilities, thermal and oxidative stability, and the transport properties of SIBS. The SIBS‐g‐PVPA SO3H membrane presented high Nafion®normalized selectivity and separation efficiency, indicating that this ionomer adequately functions for both applications.