Synthesis, microstructures, and gas separation performance of norbornyl bis-benzocyclobutene-Tröger's base polymers derived from pure regioisomers

Abstract

The chain configuration significantly influences the microstructures and gas separation performance of polymers of intrinsic microporosity. Herein, pure regioisomers of norbornyl bis-benzocyclobutene-containing (N2BC) diamines, i.e. anti-CANAL-4-MeNH₂, syn-CANAL-4-MeNH₂, anti-CANAL-2-Me₂NH₂, and syn-CANAL-2-Me₂NH₂, were prepared through Pd-catalyzed arene-norbornene annulation (CANAL) reactions, and the isomers were separated by column chromatography. CANAL-TB polymers with defined distributions of methyl and TB groups were then prepared from the above isomers. The isomeric effects of methyl and TB groups on the properties of these polymers were investigated. Anti-CANAL-TB-2 exhibited a higher Brunauer–Emmett–Teller surface area (S_BET), higher fractional free volume (FFV), and greater interchain distance relative to syn-CANAL-TB-2. In contrast, anti-CANAL-TB-4 displayed lower S_BET and FFV than syn-CANAL-TB-4. Furthermore, anti-CANAL-TB-4 exhibited a unimodal size distribution of ultramicropores, while syn-CANAL-TB-4 had a bimodal size distribution of ultramicropores. Consequently, syn-CANAL-TB-4 possessed simultaneously higher gas permeability and perm-selectivity compared with anti-CANAL-TB-4, with its H₂/CH₄, H₂/N₂ and O₂/N₂ separation performances approaching the 2015 Robeson's upper bounds.