CO₂ Adsorption on PIMs Studied with ¹³C NMR Spectroscopy

Polymers of intrinsic microporosity (PIMs) can be functionalized with nitrogen-bearing groups, such as a nitrile group for PIM-1 and a methylated tetrazole group for MTZ-PIM, to physisorb CO₂. Static ¹³C NMR spectroscopy was used to investigate CO₂ dynamics by analysis of one-dimensional spectra and T₂ relaxation times at temperatures ranging from 6 to 295 K. Each polymer had two different loadings of CO₂ to determine the dominating relaxation mechanism at lower temperatures and deduce the identity of the weaker secondary adsorption site on the rigid polymer backbone. Both polymers, with a high loading of CO₂, experience a narrowing of the ¹³C NMR line width as the samples are warmed to 80 K, which is the onset of the weakly adsorbed CO₂ hopping on and off the polymer backbone.