Influence of Resins on the Structure and Dynamics of SBR Compounds: A Solid-State NMR Study

The tackifying effect of resins used in the tire industry highly depends on the compatibility and interaction strength with the rubber matrix. Here, uncured and cured styrene/butadiene rubber compounds, either in the presence or absence of a hydrocarbon aromatic tackifying resin, were studied by means of high-resolution and time-domain solid-state NMR (SSNMR) techniques to investigate resin/polymer interactions and the effect of the resin on the dynamics of polymer chains. 13C direct excitation and cross-polarization spectra, combined with low-field measurements of 1H T1 and analysis of 1H on-resonance free-induction decay, provided information on the dynamic heterogeneity of the samples and the degree of mixing between the resin and the rubber matrix. Moreover, 1H T1 and T1ρ relaxation times at variable temperatures were used to investigate the effect of resin on both segmental dynamics activated at the glass transition and collective polymer dynamics. SSNMR findings were discussed in relation to crosslink density and Tg data. The obtained results show that the resin is intimately mixed with the polymer, while maintaining its rigid character. A slowdown of segmental dynamics, related to an increase in Tg, was found as a consequence of resin addition, while no effect was evidenced on fragility and collective polymer dynamics