# Time Domain NMR in Polymer Science: From the Laboratory to the Industry
## 3 Applications
### Discovery and Characterization of New Materials
Monitoring the reduction of rigid fraction from below the PBA T\({}_{\text{g}}\) towards higher temperatures, two softening regions were detected, as shown in Figure 9: the first one corresponding to the complete mobilization of PBA protons above T\({}_{\text{g}}\), a second one at higher temperature than PS T\({}_{\text{g}}\), where the system starts to reptate and no rigid fraction remains. In between these two transitions only PS protons contribute to rigid fraction [51]. Furthermore, common plastics can acquire a plethora of new perspectives, depending on chemical modification or manufacturing. An example is given by the fabrication of PS-based polyHIPEs (polymerized high internal phase emulsions) [52], which are studied because of their easily tunable properties, especially their high porosity. A good understanding of polyHIPEs structure and its origin is fundamental to obtain good homogeneity of the material and good control over the properties. The effect of the introduction of para-DVB (para-divinylbenzene) was investigated. [PERSON] et al. measuring \({}^{1}\)H T\({}_{1}\) and \({}^{1}\)H T\({}_{1\sigma}\), to explore both local and segmental motions, concluded that a higher content of DVB creates a network with small clusters of chains, allowing greater freedom of rotation of phenyl groups and a greater alignment of chains. Further addition of para-DVB reduces both parameters, an indication of a more mobile but disordered structure. These assumptions correlate well with the strong decreasing of the elastic modulus (Table 2 in reference [52]). Other porous materials that have attracted interest as study subjects for TD-NMR are hydrogels, which are particularly relevant as biotechnological platforms. Especially PVA (poly vinyl alcohol) underwent a thorough investigation, thanks to its biocompatibility. Some studies were conducted to gain insights into the structure of PVA cryo-gels, analyzing the process of gelation. Increasing the number of freeze-thaw cycles, the D\({}_{\text{res}}\) increases through the formation of rigid polymer areas, probably crystallites. This process is completely thermo-reversible, according to the simultaneous reduction of rigid fraction and constant D\({}_{\text{res}}\) with higher temperatures, allowing to formulate a mechanism consisting of the melting of secondary and primary crystals up to a threshold temperature where both rigid fraction and D\({}_{\text{res}}\) becomes null, that corresponds to transform the gel into an isotropic aqueous solution [53]. Removing the water out of a chemically crosslinked gel, a xerogel is obtained. In reference [54], PVA crosslinked with glutaraldehyde (GA) was characterized taking \({}^{1}\)H T\({}_{1}\) as structure descriptor. It turned out to be very sensitive both to crosslinking degree and to loading with silica, both of them inducing a reduction in \({}^{1}\)H T\({}_{1}\) due to the decreased number of hydroxyl moieties available for hydrogen bonding. That also highlighted the existence of an interaction between PVA  
Figure 9: Temperature dependence of PBA@PS core-shell nanoparticles rigid fraction. The inset highlights the region close to room temperature, showing an agreement of the composition with the expected composition derived from the synthesis feed, indicated by the solid line (Reprinted with permission from reference [51]. Copyright 2016 Wiley). and silica, that was not detected before with other techniques. \({}^{1}\)H T\({}_{1}\) also has the possibility to estimate the extent of spin diffusion path length, that means the length of spatial homogeneity, which decreases with both the crosslinking and loading. Functional composites materials response has also been characterized, especially concerning the realization of optical devices to exploit photophysical processes in photon harvesting. To match the need for solid supports and a high diffusion path length to ease the probability for the active molecules to get in contact with each other, polymers are addressed as the most adequate matrixes.