EFFECT OF CROSS-LINKING ON DYNAMICS OF ELASTOMERS:INSIGHTS FROM 1H FIELD CYCLING NMR

Long polymers experience very complex dynamics covering wide time and spatial scales. (1) 1H ?eld-cycling (FC) NMR relaxometry is an ideal technique to characterize polymer dynamics. (2) Indeed, measurements of 1H longitudinal relaxation rates (R1 = 1=T1) at di?erent Larmor frequencies allow to study dynamics on a huge range of motion times, especially by combining experiments at di?erent temperatures based on the frequency temperature superposition (FTS) principle. Achieving an in-depth comprehension of dynamics is fundamental in the ?eld of elastomers. In rubber technology, chemical cross-linking and/or the addition of ?llers are employed to get elastomers with enhanced elasticity and mechanical properties. The improved mechanical properties arise from the restrictions on chain mobility imposed by the new constrains, and a full understanding of these e?ects could be of valuable help for the design of materials with optimized performances. In this work, 1H FC NMR was employed to investigate dynamics of elastomers of technological interest for the tire industry. In particular, experiments were carried out over a wide temperature range on polyisoprene, polybutadiene, and poly(styrene-co-butadiene) rubbers, uncured and vulcanized under different conditions. (3) The obtained results pointed out signi?cant di?erences between uncured and cross-linked elastomers, disclosing insights into the e?ect of cross-linking on local glassy dynamics as well as on slower and longer-range motions of the polymer chains. (1) M. Doi et al., The Theory of Polymer Dynamics; Science Publication: Oxford, London, 1986. (2) R. Kimmich et al., Adv. Polym. Sci., 170 (2004), 1-113 (3) F. Martini et al., Macromolecules, 53 (2020), 10028-1003