Highly Conducting Anion-Exchange Membranes Based on Cross-Linked Poly(norbornene): Ring Opening Metathesis Polymerization

A series of cross-linked (XL) anion-exchange membranes (AEMs) were synthesized on the basis of the ring opening metathesis polymerization (ROMP) of norbornene monomers (rPNB). Poly(bromopropyl norbornene)-block-poly(butyl norbornene) diblock copolymers and poly(bromopropyl norbornene) homopolymers have an all-hydrocarbon backbone and a high ion-exchange capacity (IEC), up to 4.73 mequiv/g. N,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHDA) was used as a cross-linking agent to control the water uptake and mechanical instability. The cross-linked (20 mol % concentration) membrane made from high molecular weight poly(bromopropyl norbornene) (XL20-rPNB-LY100) had the highest conductivity of 99 mS/cm at 25 °C and 195 mS/cm at 80 °C. The alkaline stability of the best membrane was excellent with no detectable degradation in conductivity after 792 h in 1 M NaOH at 80 °C. Membranes were successfully tested as the polymer electrolyte in an AEM fuel cell.