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
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
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.