# Time Domain NMR in Polymer Science: From the Laboratory to the Industry
## 3 Applications
### Industrial Applications
No correlation is detected between the two variables (Reprinted with permission from reference [111]. Copyright 2013 Royal Society of Chemistry). of polyurethane (PU) were swelled with mixtures of acetone and water in different proportions. Decomposition of FID signal in at least six components allowed to observe that the mechanism of swelling depends on the composition of the swelling medium [115]. An even more interesting finding was the possibility to correlate the mechanical properties of the polymer with its relaxation behavior. For the same system PS-SBR, the elastic modulus correlated with the slower T\({}_{2}\), while the stretching exponent showed a good correlation with the elongation at break (Figure 21b) [114]. In PU foams, soft and hard components mix only to a limited extent. The degree of mixing can be calculated from the difference between the hard component proton fraction from NMR and the expected one from the formulation recipe. The T\({}_{2}\) of the soft domain showed a correlation with the foam recovery time, i.e., a decrease with increasing T\({}_{2}\) (Figure 21c). Another correlation was found with the viscous dampening (tan8) with higher values at lower mobility [116]. Furthermore, stress-relaxation has been monitored with the compositional variation in semi-crystalline polymers, analyzing samples of PVDF, which has major applications in flexible risers for oil production. Stress-relaxation under strain is accompanied by a decrease in crystallinity, with a contingent increase in the rigid-amorphous phase [117]. It has a great outcome in evaluating the material stability in retaining its mechanical properties at precise operative conditions. The improvements caused by changes in the formulation can also be studied, for example, the impact of different crosslinkers [66], stabilizers [107] or plasticizers. The introduction of new plasticizers had been the focus of [PERSON] et al. [118] in a common resin employed as adhesive, such as  
Figure 21: Connection of NMR parameters to chemical or physical properties. (**a**) T\({}_{2}\) distributions (at 30 \({}^{\circ}\)C) have been found varying according to the composition of a rubbery component, such as SBS, in a thermoplastic matrix, such as PS. The experimental distribution can be described as a superposition of the relaxation of the neat components (Reprinted with permission from reference [114]. Copyright 2007 Elsevier). (**b**) Correlation between the stretching exponent \(b\) of the fitting function for T\({}_{2}\) and the strain at break, showing a kink that has been attributed to a decreasing benefit of heterogeneity (\(b<0.9\)) (Reprinted with permission from reference [114]. Copyright 2007 Elsevier). (**c**) Variation of the foam recovery time as a function of T\({}_{2}\) for the soft component in PU foams (Reprinted with permission from reference [116]. Copyright 2015 Elsevier). hexamethylenetetramine (HMTA). T\({}_{1}\) relaxation proved to be a viable parameter to compare the efficiency of different plasticizers and its change with concentration, according to the assumption that a higher T\({}_{1}\) is related to more hindered mobility, thus a more rigid system, which, in this case, depends on a higher crosslinking degree [118]. Both reactive [119] and nonreactive [120] plasticizers have been taken into account, and the complete mechanism of action was further highlighted with DSC and FTIR measurements. More detailed monitoring of the crosslinking reaction at different temperatures was proposed in a subsequent paper [120]. The fundamental role of a properly solubilized plasticizer was clarified in terms of reduction of the temperature onset of crosslinking reaction and increase of the final crosslink density. MQ measurements can also be applied to follow the progress of a chemical reaction [121], typically it can be the curing reaction, although it is necessary to employ a single-point approach, measuring at a fixed DQ time, chosen near the maximum of the DQ build-up.