# A Wide-Ranging NMR Probe for Multiscale Structures
## 5 Applications
### Polymers
When polymers were analyzed below their glass transition temperature, the slow exchange between xenon inside and outside the particles caused different peaks to appear in the spectra (Figure 6). On the other hand, when temperature was increased above the \(T_{\rm g}\), as in the case of poly(butyl acrylate-_co_-methyl methacrylate) (\(T_{\rm g}\approx 32\)\({}^{\circ}\)C) at 60 \({}^{\circ}\)C, a single peak was observed, indicating fast exchange between different environments on the NMR time scale. The analysis of chemical shift and line width data allowed determination of the rate constant of the xenon penetration in the particles, which was observed to be independent on the xenon gas pressure and on the nature of the latex. Thus, it was shown that information regarding the core of the particles and the exchange of xenon between polymer and bulk could be obtained. Figure 6: Variable temperature \({}^{129}\)Xe NMR spectra of xenon dissolved in a polystyrene colloid below the glass transition temperature (\(T_{\rm g}=107\)\({}^{\circ}\)C). Reprinted with permission from reference [92]. Copyright 2006 _Journal of Colloid and Interface Science_. In another work, hyperpolarized \({}^{129}\)Xe NMR was used to monitor the mini-emulsion polymerization of styrene [93]. The polymerization was carried out directly in the NMR instrument, and spectra were acquired at different reaction times. By analyzing the dependence of the chemical shift on the time of acquisition, the authors found that this parameter correlated with the monomer/polymer ratio, allowing the direct monitoring of the polymerization. Moreover, this approach allowed the two different kinetic profiles given by two different initiators to be distinguished between. To validate the results, calorimetric data were acquired, and good agreement was observed between these and chemical shift data. Polymers of intrinsic microporosity (PIMs) are polymers which possess permanent pore sizes below 2 nm due to their rigid and complex structures that do not fill the space efficiently. They can be used for gas storage, gas and liquid separation, preparation of membranes, and sensing [94]. Thorough characterization of their porous structure is crucial in determining their properties and their performances in various applications. In 2010, \({}^{129}\)Xe NMR was used to study two spirobiluorene-based PIMs with different linkers [95]. \(\delta_{\mathrm{S}}\) was extrapolated from variable pressure data and used to determine the average pore diameters, which were <0.8 nm in both cases, showing that the linkers did not have a significant influence on this value. Since the size of the pores created by the structural units of these polymers was predicted to be around 1.2-1.4 nm, the authors concluded that their porous structures were created by interdigitated structural units and deformed pores, possibly generated due to incomplete condensation reactions during the synthesis. Direct comparison between PALS and \({}^{129}\)Xe NMR on an ethanoanthracene-based PIM synthesized by Troger's base formation (PIM-EA-TB) further confirmed the applicability of this technique in the characterization of porosity in this class of materials [96]. [PERSON] Mesoporous Silica  
The extensive study of mesoporous silica by means of \({}^{129}\)Xe NMR began in 1993 with the work published by [PERSON] et al., in which Equation (10) was proposed [8]. Afterwards, many other papers on this type of materials were published[PERSON]  
For example, in 2002, a thorough NMR study on ordered mesoporous silica (OMS) materials and their counterparts functionalized with alkyl silanes (referred to as PNNL materials) was conducted by Ripmeester, [PERSON], and co-workers [9]. Nitrogen adsorption measurements and TEM indicated the presence of regular porous channels with different sizes.