STRUCTURE AND DYNAMICS OF ELASTOMERIC MATERIALS BY MEANS OF 1H TIME-DOMAIN NMR: EFFECT OF CROSS-LINKING

Elastomeric materials are nowadays of central importance in many elds of application, where they need to full specic mechanical requirements. The mechanical properties of an elastomeric material take their origin on the features and topology of the polymer network. In fact xed chemical cross-links and physical entanglements among polymer chains impose notable restrictions on chain mobility and are at the basis of rubber elasticity [1]. An additional reinforcement eect can be achieved by incorporation in the rubber matrix of dierent nanoparticles, such as carbon black, carbon nanotubes, nanosilica, and clays [2, 3]. So far extensive research eorts have been addressed to the comprehension of the relationships between the \molecular" and mechanical properties of elastomeric materials, but a full understanding is still lacking. In this frame, NMR spectroscopy can play an important role giving access to many structural and dynamics information on wide spatial and time scales. In this work we applied a combination of dierent time-domain NMR (TD-NMR) techniques to the study of elastomeric materials based on isoprene, butadiene and styrene-butadiene rubbers, with application in the tyre industry. In particular the in uence of chemical cross-links on the polymer chain dynamics in a wide spectrum of motion frequencies was investigated, by studying samples obtained using dierent vulcanization conditions. 1H Multiple Quantum (MQ) experiments [4] were used for the measurement of the residual 1H-1H dipolar interaction: the latter is dependent on the anisotopic character of the fast reorietations of chain segments and, therefore, it is related to the amount and distribution of the topological constraints within the polymer network. Further and complementary information on dierent regimes of polymer dynamics were also obtained by means of measurements of 1H spin-spin relaxation times (T2) and variable temperature 1H T1 Fast Field Cycling (FFC) [5] experiments. References: [1] S. Schl?ogl, M. L. Trutschel, W. Chasse, G. Riess, K. Saalw?achter Macromolecules 47, 2759-2773, (2014). [2] R. Scotti, M. D'Arienzo, B. Di Credico, L. Giannini, F. Morazzoni, Silica-Polymer Interface and Mechanical Reinforcement in Rubber Nanocomposites. In Hybrid Organic-Inorganic Interfaces; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, pp. 151-198, (2017). [3] G. Kraus, Reinforcement of Elastomers; Interscience Publishers: New York, (1965). [4] K. Saalw?achter Prog. Nucl. Mag. Res. Sp. 51, 1-35, (2007). [5] R. Kimmich, Field-cycling NMR Relaxometry: Instrumentation, Model Theories and Applications; The Royal Society of Chemistry, (2019).