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Design and characterization of azo-linked porous organic polymers

Porous organic polymers (POPs) are solid materials which are built by covalently linking organic molecular building blocks of different geometries and topologies. Characteristics of POPs such as large specific surface area, high porosity, high chemical and thermal stability and low density, make them suitable for a range of applications, especially in gas storage and separation. For example, POPs containing azo linkages were found to exhibit high affinity for CO2 uptake and low affinity towards N2, making them as good candidates in post-combustion CO2 capture and for highly selective gas separations. In the present study, we synthesized several new azo-linked polymers by coupling of 1, 3, 5-tris(4- nitrophenyl)benzene with various aromatic diamino compounds, differing in length and rigidity, under basic conditions. The obtained polymers are insoluble in common organic solvents. IR and 13C CP/MAS NMR spectroscopy suggested formation of azo linkages and the presence of nitro and amino end- groups. Powder XRD data revealed amorphous nature of azo polymers while TG analysis indicated their very high thermal stability. DFT study revealed the most probable sites of interaction between the building units connected by azo bonds and gas molecules of CO2 and N2. Binding energies were calculated for both aromatic and azo groups to delineate their effects on CO2/N2 selectivity of the synthesized POPs.

Porous organic polymers, azo-linked polymers, 1, 3, 5-tris(4-nitrophenyl)benzene,

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