Considerations of macromolecular structure in the design of proton conducting polymer membranes: Graft versus diblock polyelectrolytes

Model fluorous-ionic copolymer systems were synthesized and studied to investigate the role of polymer architecture on morphology and properties of solid polymer electrolytes. Two types of compositionally similar but architecturally distinct copolymers were investigated: P(VDF-co -CTFE)-g -S PS graft copolymers, comprising a hydrophobic fluorous backbone and sulfonated styrene side chains, and P(VDF-co -HFP)-b -S PS diblock copolymers, comprising a hydrophobic fluorous segment linearly connected to a sulfonated styrenic segment. The macromolecular structure plays an important role in determining membrane morphology. Graft membranes possess a small ionic cluster morphology while diblock membranes possess a lamellar-like morphology. These morphological differences affect the threshold of ionic percolation, water sorption, proton mobility and concentration, proton conductivity, and anisotropy of ion conduction.