Thermoplastic silicone elastomers based on Gemini ionic crosslinks

Abstract

Traditional silicone elastomers are thermoset polymers with crosslink sites linked through covalent bonds. The benefits of silicone elastomers would be improved by the ability to reuse the materials. Here we report an ionically crosslinked thermoplastic, silicone material based on acid/base neutralization. Dicarboxylic acid silicones were prepared by the Michael-addition to maleic acid of thiopropylsilicones. A range of materials was prepared by incorporating different concentrations of maleic acid on the silicone backbone. Gemini (double ionic) crosslink sites were established by neutralizing both COOH groups with β-diaminoethylsilicones. The combination of these two difunctional agents was synergistic; stronger mechanical properties were observed than for materials with analogous crosslink densities arising from monofunctional ions. The physical properties of the elastomers were dynamic. The ionic networks showed competitive mechanical strength compared to their covalently crosslinked counterparts under fast deformation but exhibited much higher extension (>1200%) under slow deformation. The ionic interactions could be easily overcome thermally.