Self-healing behavior in blends of PDMS-based polyurethane ionomers

Ionic interactions offer the highest non-covalent cohesive strength in supramolecular assemblies. In spite of that, they have been consistently underestimated in the development of self-healing materials due to their lack of directionality and association specificity. In this paper, ionic moieties are introduced as side-chain pendants in poly(urea-urethane) siloxane-based polymers, aiming to obtain a strong yet flexible elastomer with the capability to recover from a damaged state. The synthesis was carried out by a two-step polymerization involving polydimethylsiloxane (PDMS) diamine-terminated, isophorone diisocyanate (IPDI) and a chain extender providing the required ionic functionality. Internal phase separation allowed the material to show its elastomeric behavior. After preparation of the blend by mechanical mixing, the formation of ionic interactions was checked for by FT-IR spectroscopy, rheological analysis and tensile tests. Healing of notch damage was evaluated both with respect to tensile strength and fracture toughness. At room temperature (21°C) and humidity (30% RH) the maximum recovery measured at 14 days was 47%. Self-healing dependence on humidity and temperature was assessed, resulting in further improvements (up to 100%) as molecular mobility was increased by both conditions.