Block Co-Polymer like Phase Behavior in Ionic Elastomer

Predominantly, the mechanical properties of ionic elastomers are largely governed by the ionic clusters formed during the crosslinking of the elastomers with metal oxides e.g., zinc oxide. These ionic aggregates are found to promote microphase separation and exhibit additional high-temperature relaxation behavior in dynamic mechanical thermal analysis. In the present work, the nature of these ionic aggregates is intensively explored. In this study it was found that except zinc oxide, other zinc-containing compounds such as zinc-aluminum-layered double hydroxide and zinc chloride do not exhibit any extra dynamic mechanical relaxation processes at high temperature, nevertheless ionic crosslinking reactions with XNBR take place with all of these zinc compounds. In-depth analysis by Fourier-transform infrared spectroscopy and dynamic mechanical analysis revealed that this high-temperature relaxation behavior does not originate from ionic crosslinking 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 sophisticated techniques employed in transmission electron microscopy. Block copolymer like phase separated morphology are practically realized to be existing for the first time in the ionic elastomer.