CONTROLLED RELEASE ANTIFOULING COATINGS. I. APPROACHES FOR CONTROLLED RELEASE OF 2,4-DINITROPHENOLATE AND BENZOATE INTO SEAWATER

Marine coatings incorporating two model inhibitors, benzoic acid and 2,4-dinitrophenol, have been utilized to study controlled release and antifouling behaviour. Both non-ablative and ablative coatings were developed to investigate two different mechanisms of inhibitor delivery to the coating surface. Non-ablative coatings were based on commercial vinyl polymers to serve as binders for inhibitors dispersed either as pure compounds or in microcapsules. Release rates of the inhibitors into artificial seawater were measured and showed that the release from both simple films and microcapsules follow a diffusion-controlled process and correlate with the Higuchi model. Ablative, or "self-polishing" coatings were also developed to study the delivery of the model inhibitors by seawater hydrolysis of pendant arm homopolymers having the model inhibitors covalently immobilized. Poly(vinyl benzoate) films deliver benzoate with zero-order kinetics (constant rate) in the 10(-1) mu g.cm(-2).d(-1) range after an initial faster delivery period. Poly(benzoic methacrylic anhydride) films deliver benzoate over three orders of magnitude more rapidly with first order kinetics, consistent with rapid bulk hydrolysis and slower erosion of the hydrolyzed polymer. Poly(2,4-dinitrophenyl acrylate) hydrolyzes very rapidly (hours) in seawater.