Back Cover: Thermally Rearranged Polymer Membranes Containing Tröger's Base Units Have Exceptional Performance for Air Separations (Angew. Chem. Int. Ed. 18/2018)

Gas‐separation membranes rely on rigid backbones and high porosity for enhanced selectivity and permeability. In their Communication on page 4912 ff., B. A. Helms et al. demonstrate the synthesis of thermally rearranged polymer membranes containing rigid, contorted Tröger's base units that show exceptional O2/N2 separation performance. The smaller O2 molecules can “squeeze through the cracks” in the rigid polymer pore network. Credit: wall image adapted from https://flic.kr/p/nER9MF.