Characterization of Network Structure and Chain Dynamics of Elastomeric Ionomers by Means of ¹H Low-Field NMR

Abstract

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.

Epoxy resin curing reaction studied by proton multiple-quantum NMR

“…Note that 2-pulse sequence described in this scheme is named 5-pulse sequence in some previous works. [29][30][31] [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com. ]…”

“…22,30 Nevertheless, the use of B-P sequence is limited for characterizing high dipolar coupled polymers (epoxy resins would belong to this type of samples), as it was recently demonstrated in the study of ionic elastomers. 31 The main problem in these systems is the fast decay of the associated NMR signal, which completely vanishes during a single cycle of the B-P sequence ($0.09 ms). In this context, we have applied and combined two simplified versions of the B-P sequence named 2-pulse and 3-pulse sequences [32][33][34] (see Fig.…”

Significance of epoxy network properties for the toughening effect of flaky and fullerene‐like WS2 nanoparticles

“…In the recent years, it has been successfully applied to characterize the network structure of elastomers, 17,18 hydrogels, 19 and ionomers, 20 however it has not been applied to thermosets like epoxy until recently. 21 This method allows measuring a material's residual dipolar coupling D res , which corresponds to the overall rigidity of the network chains after delineating it from the FIGURE 1 Transmission electron microscopy images of NP agglomerates.…”

Intrinsic Self-Healing Polymers Based on Supramolecular Interactions: State of the Art and Future Directions

“…New methods, such as 1 H low-field NMR measurements [187], for investigating self-healing ionomers with respect to their mechanical and self-healing behavior should yield a more detailed understanding of the mechanism. These results could provide evidence for structural changes in the polymer itself, which result in improved properties of the resulting material.…”