Synthesis and characterization of butyl rubber ionomers

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Butyl rubber (isobutylene-isoprene rubber, IIR) is a material with unusual physical properties, useful in different areas including automotive, architectural, and biomedical applications. A good resilience (shape recovery upon deformation) is necessary for all these applications. This is possible for IIR because the polymer chains contain a low concentration (1-2%) of isoprene (unsaturated) units in addition to isobutylene, allowing covalent (permanent) cross-linking of the chains into a 3-dimensional network structure. The covalent bonding approach, while providing good dimensional stability, allows only limited control over the mechanical properties of the material. Ionic interactions, on the other hand, are known to be very useful to modify the mechanical properties (e.g. rigidity, softening temperature, tear resistance) of rubbers and plastics, and have found applications in commercial products such as the Surlyn® resins, used as highly tear-resistant materials for blister packaging. The improved properties of polymers containing a low concentration of polymer-bound ionic groups (ionomers) are attributed to the aggregation of the ionic moieties, acting as multivalent physical cross-links at low to moderate temperatures. The application of the ionomer concept to improve the mechanical properties of butyl rubber has received little attention, mainly due to the very low (1-2%) isoprene content achieved in the traditional butyl rubber synthesis. New processes developed recently at LANXESS Inc. allow the synthesis of butyl rubber containing 1) up to 5-6% of isoprene units, or 2) up to 10% of p-methylstyrene units. This would allow the synthesis of ionomers with higher ionic moieties contents, and correspondingly a much wider range of mechanical properties than for traditional IIR. In the proposed project, reaction conditions will be established for the derivatization of high isoprene content IIR and of p-methylstyrene-modified IIR to novel ionomers by different techniques, and the mechanical properties of the resulting polymers will be investigated to correlate their structure with the observed properties. These butyl rubber ionomers are emerging materials of interest for applications in areas including the automotive industry.