Evidence for an in Situ Developed Polymer Phase in Ionic Elastomers

Abstract

The overall mechanical performance of ionic elastomers, such as carboxylated nitrile rubber (XNBR), is largely governed by ionic clusters formed during the cross-linking of the elastomers with zinc oxide. These ionic aggregates promote microphase separation and show additional high-temperature relaxation behavior in dynamic mechanical analysis. In this study, the nature of these ionic aggregates is explored for the first time. We find that some zinc-containing compounds, such as zinc–aluminum-layered double hydroxide and zinc chloride, do not exhibit any extra high-temperature dynamic mechanical relaxation processes, although ionic cross-linking reactions with XNBR occur with all of these zinc compounds. Detailed analysis by Fourier-transform infrared spectroscopy and dynamic mechanical analysis revealed that this high-temperature relaxation behavior does not originate from ionic cross-linking but is associated with the formation of an additional zinc-enriched polymer phase that arises due to reactions between carboxylic groups and zinc oxide. Infrared spectroscopic investigation indicates further that a tetrahedrally coordinated complex facilitates the formation of a zinc–carboxylic polymeric network. Clear microphase separation of the ionic polymer in the elastomer could be directly visualized by transmission electron microscopy for the first time.

Hysteretic damping in XNBR – MWNT nanocomposites at low and high compressive strains

“…However, when sufficient time was given up to 240 h, intensity of the peaks found to increase significantly. This trend confirms the labile and reversible nature of the ionic phase [31]. On close observation, it can be seen that the intensity is indeed more than the unheated original sample itself, probably due to the enhanced reordering of the ionic structure consequent to the re-alignment of the macromolecules upon heating to 150°C.…”

Phase changing stearate ions as active fillers in multifunctional carboxylated acrylonitrile–butadiene composite: Exploring the role of zinc stearate

“…Figure (a) demonstrates the MDR rheographs for the different rubber composites cured at 160 °C until 1 h, and therein, the XNBR–ZnO specimen clearly shows the highest uniform rheometric torque ~6 dNm among all other specimens that contain ZnSt. This is attributably due to the formation of zinc carboxylate ionic linkage in the XNBR–ZnO that considerably raises its elastic modulus . Further, it can be seen from this figure that the addition of ZnSt to XNBR–ZnO had the effect of significantly lowering the elastic modulus initially.…”

“…Some of the present authors have previously shown that XNBR, a functional elastomer can also form ionomeric polymer composites and the microstructure of these composites could be resembled with ionomeric shape memory composite particularly, when treated with zinc oxide …”

“…Entire mechanism of formation of ionomers is based on the following phenomenon; ion pairs are formed followed by the formation of multiplets . Multiplets are basically termed as aggregates consisting of several ion pairs (approximately 6–8) . The scope to tune the structure–property relationship as per requirement in such nanostructured ionomer provided by their architectural versatility offers immense liberty to the material scientists to design and develop smart products .…”

“…Multiplets are basically termed as aggregates consisting of several ion pairs (approximately 6–8) . The scope to tune the structure–property relationship as per requirement in such nanostructured ionomer provided by their architectural versatility offers immense liberty to the material scientists to design and develop smart products . Hence, function integrated properties are the denouements from such materials.…”