NMR cryoporometry of polymers: Cross-linking, porosity and the importance of probe liquid

The morphology of cross-linked polymers plays an important role in their physical and chemical properties. NMR cryoporometry allows for the investigation of these structures over different length scales, through appropriate choice of probe liquid. The different structures of two different polymeric samples, one a cross-linked polymer hydrogel, the other a pore-expanded ion-exchange polymer, are analysed here. The ability for NMR cryoporometry to analyse both polymeric materials in the swollen state is successfully demonstrated, as is the importance of probe-liquid choice for the analysis of different regions of the pore structure. In both cases, water is used to identify populations of pores smaller than ca. 5 nm. The use of t-butanol and menthol reveals the presence of additional mesoporous structures in the ion-exchange resin as well as the responsiveness of the pore structure to the liquid used to swell it.