## 4 Conclusions  
In this work, the effects of the tackifying resin Kristalex(tm) 5140 on the structural and dynamic properties of SBR compounds of interest to the tire industry were investigated through a combination of high-resolution and TD SSNMR techniques. To this end, uncured and cured SBR compounds, either in the absence or presence of 15 phr of resin, as well as a pure Kristalex(tm) 5140 sample, were studied, and the obtained results were discussed in comparison with \(T_{\rm g}\) and crosslink density data. From the \"macroscopic\" point of view, an increase in \(T_{\rm g}\) and a slight decrease in crosslink density were observed as a consequence of resin addition. From the \"microscopic\" point of view, the resin was found to be intimately mixed with the polymer in the rubber matrix, while maintaining its rigid character. Moreover, the resin induced a slowdown of segmental dynamics of the polymer in both uncured and cured samples, while it did not affect the polymer fragility and the spectrum of collective polymer motions in the Rouse regime. In conclusion, the obtained results showed for the first time that SSNMR can provide very useful information on the degree of mixing and interaction between resin and polymer in rubber compounds. This information could help the comprehension of the molecular origin of the observed macroscopic and mechanical properties, which is fundamental to drive research towards formulations with improved and optimized performances. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13031939/s1](https://www.mdpi.com/article/10.3390/app13031939/s1)]([https://www.mdpi.com/article/10.3390/app13031939/s1](https://www.mdpi.com/article/10.3390/app13031939/s1)), Figure S1: \({}^{1}\)H FID (black points) and Gaussian fitting function (green line) obtained for Kristalex; Figure S2: Integral intensities of the \({}^{13}\)C CP/MAS signals (points) and fitting functions (black lines) obtained for vSBR (**a**), vSBR_k (**b**) and Kristalex (**c**) as a function of the contact time \(\tau_{\text{CP}}\); Figure S3: \({}^{1}\)H NMR susceptibility curves of the investigated samples at the indicated temperatures. Table S1: \(T_{\text{CH}}\) and \(T_{1\rho}\) values obtained from the analysis of the CP curves for the investigated samples; Table S2: \({}^{1}\)H \(T_{1\rho,i}\) values and relative weight percentages (\(W_{i}\)) obtained for vSBR and vSBR_k at the investigated temperatures; Table S3: \({}^{1}\)H \(R_{1\rho}\)\({}^{PWRA}_{1\rho}\) (experimental), \(R_{1\rho}\)\({}^{vS}\) (calculated) and \(R_{1\rho}\)\({}^{pol}\) (calculated) obtained for vSBR and vSBR_k at the investigated temperatures. M.P. and F.N. ([PERSON]) contributed equally to this work. Conceptualization, M.G., F.M., F.N. ([PERSON]) and L.C. ; methodology, all authors; software, M.P., F.N. ([PERSON]), F.M. and F.N. ([PERSON]); validation, M.P., F.N. ([PERSON]), F.M. and F.N. ([PERSON]); formal analysis, M.P., F.N. ([PERSON]), F.M., F.N. ([PERSON]), L.C. and M.C. ; investigation, F.M., F.N. ([PERSON]), M.P., F.N. ([PERSON]) and L.C. ; resources, M.C., L.G., L.C., F.M. and M.G. ; data curation, M.P., F.N. ([PERSON]), F.M., F.N. ([PERSON]), L.C. and M.C. ; writing--original draft preparation, F.M., F.N. ([PERSON]), L.C., M.P., F.N. ([PERSON]), M.G. and M.C. ; writing--review and editing, all authors; visualization, F.M., F.N. ([PERSON]), M.P. and [PERSON]. ([PERSON]); supervision, M.C., L.G. and M.G. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The data presented in this study are available on request from the corresponding authors. CISUP (Center for Instrument Sharing-University of Pisa) is acknowledged for the use of the Bruker Avance Neo 500 solid-state NMR spectrometer. [PERSON] acknowledges MUR (Ministero dell'Universita e della Ricerca) for the project PON 2014-2020 (D.M.