The network structure and chain dynamics of ionic elastomers based on carboxylated nitrile rubber (XNBR) cross-linked with different content of magnesium oxide (MgO) have been studied by different low-field time-domain NMR experiments. Ionic contacts created during the vulcanization tend to aggregate trapping some polymer segments that show restricted mobility as it was quantified by analyses of refocused free induction decays. Increasing the MgO content above the stoichiometric fraction has no effect on the amount of trapped polymer segments, but it increases the network cross-link density as measured by multiple-quantum (MQ) NMR experiments. The central finding of this work is that MgO addition above the stoichiometric content enhances the mechanical properties by creating a larger number of smaller ionic clusters, which act as dynamic cross-links, but are not readily seen by other techniques. Changes in the network structure and morphology of segregated thermolabile ionic domains have an impact on the ionic rearrangement dynamics and, in consequence, on the thermoplastic behavior of these materials at elevated temperatures.

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Elastomeric composites have been prepared using pre-treated fumed silica as a reinforcing system. The processing disadvantages of fumed silica were overcome by a novel one-pot modification method based on silanization treatment of silica particles after an ultra-high energy sonication process that breaks down the micro-aggregates/agglomerates of pristine silica into nanoparticles. Grafted organosilane molecules on the nanoparticle surfaces avoid the natural tendency for silica particles to re-agglomerate obtaining a stable dispersion of organo nanosilica particles that are compatible with the rubber matrix. The modified nanosilica can be easily incorporated into the elastomer matrix by conventional methods employed in rubber technology, contrary to pristine fumed silica which shows significant compounding disadvantages leading to high viscosity compounds. The improved dispersion and enhanced interface significantly enhance the final properties of the composites. Finally, the filler-rubber interface was characterized combining 1 H low field Double Quantum (DQ) NMR spectroscopy and equilibrium swelling experiments. This novel experimental methodology demonstrates the existence of improved interactions in the interface between silica particles and rubber macromolecules.