Intrinsische Selbstheilung von Beschichtungssystemen

Abstract

In the present dissertation, two novel polyurethane-polyurea-based polymeric materials equipped with a high number of reversible hydrogen bonds (HBs) were examined in detail and characterized for their intrinsically self-healing properties. The chemical (covalent bonds) and physical (HB) network density of the polymers was varied by the self-healing reagent 1- (2-aminoethyl) imidazolidone (UDETA). Two different stimuli were identified for successful self-healing - increased relative humidity (23 degree C, 22-90 % RH) and elevated temperature (80-130 degree C). For self-healing at room temperature the presence of reversible HBs which provide higher molecular dynamics of the binding partners for self-healing process after bond breakage is of central importance. This circumstance was experimentally confirmed by the (temperature)-modulated differential scanning calorimetry (MDSC) measurement. It was found that the polymer absorbed water which is "strongly" bonded via HB within the polymeric network. This water causes a plastification of the material. Time domain Nuclear Magnetic Resonance (TD-NMR) measurements showed that with increasing UDETA content, a higher mobile fraction is present in the polymer. The mobility of the polymeric chains can be increased by incorporation of water, achieving a positive effect on the self-healing efficiency of the polymers. The importance and availability of different HB species in the polymer were examined in detail with Fourier Transformation Infrared (FT-IR) spectroscopy after equilibrating the samples with D2O. With increasing UDETA content the self-healing polymers show an increasing number of free carbonyl groups which were not bound via HB with varying strength. This work has successfully demonstrated the synthesis of intrinsically self-healing polyurethane-polyurea polymers and elucidated fundamental mechanistic questions of self-healing. The investigations underline the high potential of this investigated coating in a potential application.