Imidazole containing polymers complexed with Cu2+ and Zn2+

Licentiate thesis, 2009

An enormous problem for the shipping industry is fouling of marine organisms such as algae and barnacles on the boat hull. The negative consequences for the society are both economical as well as environmental. To prevent fouling in general, biocides are typically incorporated directly into the paint. Premature leakage of the biocides is a drawback which reduces the lifetime of the coating and pollutes the surrounding ecosystems. Microencapsulation is an efficient way of encapsulating active substances for controlling the release and thereby prolonging the antifouling properties of the coating. The rate of release into the marine environment is partly governed by the degree of swelling of the shell of the microcapsule. The swelling of the microcapsule shell, and hence the release of biocide, may be modified by utilizing imidazole coordination chemistry towards metal ions in the shell material. The aim of this thesis has been to characterize such coordinating polymer complexes and evaluate their material properties, solubility characteristics and coordination chemistry as well as synthesising new materials. Furthermore it is of interest to outline the coordination properties of imidazole as a function of substitution position since synthetic and natural imidazole ligands in polymers are typically substituted at position 1 or 4. The coordinating polymer material was studied using DSC, mid-FTIR and far-FTIR vibrational spectroscopy as well as simple ocular investigation. The coordination chemistry of the coordinating polymer material and related coordination compounds were evaluated by far-FTIR and EPR. The reaction between the polymer and the metal ions Cu2+ and Zn2+ cross-links the system and increases the glass transition temperature, Tg. Furthermore, the strong coordinate bond between imidazole and the metal ions in the cross-links renders the complex insoluble in conventional solvents, and only strongly coordinating solvents are able to solubilise the complex. The geometry of the Cu2+ complexes is square planar with up to four imidazole ligands and the physical properties of corresponding the Zn2+ complexes indicate a higher coordination number. The metal ions are exclusively coordinated by the imidazole ligand in the polymer. Concerning the effect of ring substitution on the coordination chemistry of imidazole, the results indicate that the inductive effect of the group attached has a much larger effect than the position of the group. iv Due to the significant strength of the coordinate bond, coordination of imidazole by Cu2+ or Zn2+ is an efficient way of almost irreversibly incorporating salts into a hydrophobic polymer material. Polymers coordinated by metal ions provide the resulting coordinating polymer complex with new material properties. The specific aim of this doctoral project is to use these polymer materials to modify the shell of the microcapsule in order to control the rate of release. Due the strongly hygroscopic nature of salts, the tendency for the shell material to swell by water should be significantly enhanced. The contact with sea water will accordingly act as a trigger for release.