Self-healing coatings by reversible crosslinking: Mechanistic investigations of defined model systems on the molecular level using linear and non-linear Raman microspectroscopy

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Polymer coatings are essential for every modern society, protecting surfaces of an uncountable number of products. The introduction of self-healing properties would have an important impact on the lifetime of these materials. Even despite the fact that first commercial coatings with self-healing properties exist, the underlying molecular processes are far from being understood. The central target of the proposed project is the elucidation of the underlying molecular mechanisms of self-healing in coatings relying on reversible crosslinks, in particular on reversible Diels-Alder (DA) cycloadditions. In this project we propose (i) the usage of a new type of polymer containing both the diene furan and the dienophile maleimide, while varying the substitution pattern to tune the healing temperature as well as the healing efficiency, and (ii) the investigation of a new type of a hetero-Diels-Alder reactions (thioketones/dithioesters with dienes) for self-healing applications. Both types of crosslinked systems will be investigated in detail by linear and non-linear Raman microspectroscopy in combination with two-dimensional correlation analysis. For self-healing systems, such an approach has not yet been described; it will allow the investigation of damaged and non-damaged areas and, therefore, the differentiation between both. As a trigger for the self-healing process, primarily heat will be utilised; additional activators will be investigated based on the attempted increased knowledge of the basic principles and mechanisms.