Proton conducting poly(vinylidene fluoride-co-chlorotrifluoroethylene) graft copolymer electrolyte membranes

A series of proton conducting comb copolymer membranes consisting of poly(vinylidene fluoride-co-chlorotrifluoroethylene) backbone and poly(styrene sulfonic acid) (PSSA) side chains, i.e. P(VDF-co-CTFE)-g-PSSA were synthesized using atom transfer radical polymerization (ATRP). ¹H NMR, FT-IR spectroscopy, wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) results present the successful "grafting from" method using ATRP and the well-defined microphase-separated structure of the polymer electrolyte membranes. All the properties of ion exchange capacity (IEC), water uptake and proton conductivity for the membranes continuously increased with increasing PSSA contents. The results of thermal gravimetric analysis (TGA) also showed that all the membranes were stable up to 300 °C. After terminated chlorine atoms were converted to end-functional azide groups (P(VDF-co-CTFE)-g-PSSA-N₃), the polymer electrolyte membranes were crosslinked under UV irradiation. The crosslinked P(VDF-co-CTFE)-g-PSSA membrane with 73 wt.% of PSSA content exhibited the reduced water uptake from 300 to 83%, the increased tensile strength from 21.1 to 26.2 MPa and the slightly reduced proton conductivity from 0.074 to 0.068 S/cm at room temperature compared to the uncrosslinked membrane.