Fouling of marine organisms on the hulls of ships is a severe problem for the shipping industry. Many antifouling agents are based on five-membered nitrogen heterocyclic compounds, in particular imidazoles and triazoles. Moreover, imidazole and triazoles are strong ligands for Cu2+and Cu+, which are both potent antifouling agents. In this review, we summarize a decade of work within our groups concerning imidazole and triazole coordination chemistry for antifouling applications with a particular focus on the very potent antifouling agentmedetomidine. The entry starts by providing a detailed theoretical description of the azole-metal coordination chemistry. Some attention will be given to ways to functionalize polymers with azole ligands. Then, the effect of metal coordination in azole-containing polymers with respect to material properties will be discussed. Our work concerning the controlled release of antifouling agents, in particular medetomidine, using azole coordination chemistry will be reviewed. Finally, an outlook will be given describing the potential for tailoring the azole ligand chemistry in polymers with respect to Cu2+adsorption and Cu2+→Cu+reduction for antifouling coatings without added biocides.

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Polyethyleneimine (PEI) is known for its metal-coordinating properties and in its crosslinked form has applications in different areas ranging from drug delivery to waste water treatment and recovery of trace metals. With the aim to regulate the coordination environment of Cu(I) and Cu(II) ions in marine coatings, we have prepared a triazole cross-linking agent with 'soft' coordination that can crosslink PEI via indirect reductive amination. We have shown that this triazole crosslinker not only increases the Cu(II) absorption capacity of the crosslinked PEI in comparison to the traditionally used glutaraldehyde-crosslinked PEI (PEI-GA), but also allows the crosslinked polymer network to stabilize the Cu(I) oxidation state more effectively. The Cu(II) uptake and Cu(I) stabilization of the polymer have been determined by elemental analysis and UV-vis spectroscopy. It was found that the triazole-crosslinked polymer (PEI-TA) could coordinate up to 12 wt% of Cu(II) before and 6 wt% Cu(II) after imine reduction.

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