Article pubs.acs.org/Macromolecules
Evidence for an in Situ Developed Polymer Phase in Ionic Elastomers Debdipta Basu,†,‡ Amit Das,*,†,§ Klaus Werner Stöckelhuber,† Dieter Jehnichen,† Petr Formanek,† Essi Sarlin,§ Jyrki Vuorinen,§ and Gert Heinrich†,‡ †
Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Straße 6, D-01069 Dresden, Germany Institut für Werkstoffwissenschaft, Technische Universität Dresden, D-01069 Dresden, Germany § Tampere University of Technology, Department of Materials Science, Fi-33101, Tampere, Finland ‡
ABSTRACT: The overall mechanical performance of ionic elastomers, such as carboxylated nitrile rubber (XNBR), is largely governed by ionic clusters formed during the crosslinking 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.
1. INTRODUCTION Ionomers belong to a special category of polymers that contain a low level (
