Synthesis and characterization of star-shaped sulfonated new poly(ether triazole)s: Proton exchange membrane properties

Abstract

Several star-shaped sulfonated poly(ether triazole)s abbreviated as PTAPSH-XX was prepared by Cu (I) catalyzed click polymerization of a mixture of a new tri-azide monomer namely, 4,4-tris[3-trifluoromethyl-4(4-azidophenoxy)phenyl]biphenyl (PGZ) (B3) and 4,4′-diazido-2,2′-stilbene disulfonic acid disodium salt (DADSDB) with an equimolar amount 4,4′-(propane-2,2-diyl) bis((prop-2-ynyloxy)benzene) (BPEBPA). The degree of sulfonation of the prepared copolymers was varied by changing the molar ratio of DADSDB in the polymer feed. The monomer and copolymers were characterized by FTIR and NMR spectroscopic techniques. The salt form of the branched copolymers was converted into flexible membranes by solution casting technique using dimethyl sulfoxide (DMSO) as solvent and was converted to their acid form by acidification in 1.5 M H2SO4. The introduction of the branching unit largely governs the physicochemical properties and proton conductivity of the membranes. The polymers displayed desirable set of properties required proton exchange membrane applications like high thermal stability (Td10 ~ 259–290 °C), low water uptake and excellent dimensional integrity. The membranes also displayed improved mechanical properties (TS = 51 to 73 MPa, YM = 2.07 to 2.37 GPa), enhanced oxidative stability and high proton conductivity (44 to 102 mS cm−1 at 80 °C). The TEM images of the PTAPSH-XX membranes revealed excellent phase segregated morphology with the formation of ionic clusters within 15 to 90 nm.