The synthesis and optimization of novel bioactive components is key to the development of antifouling marine coatings. It was recently demonstrated that medetomidine (MM) has perfect antibarnacle behavior along with good ecological properties. To investigate the applicability of MM in self-polishing marine paints, a large set of mixtures of MM with two commercial alkyd resins (ARs) was prepared. The nature and strength of the intermolecular interaction as a function of composition in both the liquid and solid states were studied using NMR and FTIR techniques, respectively. It was found that at low concentrations MM molecules were coordinated to alkyd resin chains by hydrogen bonding. This interaction had a multidentate character (i.e., one molecule of MM interacted with several -COOH species of ARs) that resulted in stronger bonding between the two compounds. However, at higher MM concentrations an ionic association between the two compounds began, which at a large MM content resulted in microphase separation. It was noted that the strong interaction between medetomidine and the alkyd resins investigated was a positive factor for the application of these compounds in self-polishing marine paints. (c) 2005 Wiley Periodicals, Inc.