Field-Cycling NMR Relaxometry in Tire Elastomer Science

Field-cycling (FC) NMR relaxometry is an ideal tool to investigate multiscale polymer dynamics since it can give access to longitudinal relaxation rates (R₁(ω)) over a broad Larmor frequency range, which can be further extended by employing the frequency-temperature superposition principle. Applications of FC NMR on elastomers of interest for tire industry (i.e., cis-1,4-polyisoprene, cis-1,4-polybutadiene, and co-poly [styrene-butadiene]), aimed to obtain information on segmental and polymer dynamics over different regimes as a function of chain length in polymer melts and in dependence on cross-linking degree and addition of fillers or additives in rubbers, are here reviewed for the first time. After a brief presentation of theoretical tools used in data analysis, studies on polymer melts at variable temperature are reported allowing theories for polymer dynamics, such as tube reptation and renormalized Rouse models, to be tested in the entanglement regime through characteristic dependences of R₁(ω) on Larmor frequency. Then, studies on rubbers and elastomer compounds are illustrated, highlighting the effects of curing conditions (i.e., temperature, concentration of sulfur and accelerant), and the presence of reinforcing fillers and additives (e.g., tackifying resins) on segmental dynamics, related to macroscopic properties as glass transition temperature, and on collective polymer dynamics. Issues connected with the application of FC NMR relaxometry to polymeric systems with increasing structural and compositional complexity are critically discussed.