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Full Paper Self-Healing Rubbers Based on NBR Blends with Hyperbranched Polyethylenimines Andreas C. Schussele, Fritz Nubling, Yi Thomann, Oliver Carstensen, ¨ ¨ Georg Bauer, Thomas Speck, Rolf Mulhaupt* ¨ Hyperbranched PEI and urea-functionalized PEI amphiphiles are employed as additives in NBR compounding. Polarity design governing phase separation, PEI migration and PEI-mediated self-healing of NBR is demonstrated. The compatibility of PEI and NBR decreases with increasing molecular weight of PEI and with decreasing degree of substitution. Micro- phase-separated NBR/PEI blends are prepared with varying PEI molecular architectures. Thermal self-healing of NBR/PEI is monitored by apply- ing tests combining crack initiation with annealing under compression. All PEI additives show complete crack-healing upon annealing at 100 8C for 12 h. In contrast to neat NBR, the NBR/PEI-2 blend afforded a self-healing efficiency of 44% after cutting and re-join- ing by compression and annealing. 1. Introduction by incorporating non-covalent bonds into the polymer backbone. Secondly, self-healing induced by external Nitrile rubbers (NBR) find a wide range of commercial stimuli such as temperature involves the development of applications including hydrocarbon-resistant sealants as new additives which respond to mechanical and thermal well as noise and vibration dampening sandwich structures stimuli in order to trigger self-repair mechanisms. in automotive industry. An important objective in NBR The secon