Acrylic binders with covalently bound quorum sensing inhibitor units for copper-free marine antifouling coatings

The control of marine biofouling remains a major environmental challenge, as current commercial coatings still rely largely on copper oxides and organic booster biocides. Although efficient, these formulations raise serious concerns due to ecotoxicity, bioaccumulation, and increasingly restrictive regulations, especially in confined environments such as harbors, lakes, and freshwater reservoirs. Here, we report the development of a copper-free antifouling (AF) coating based on an acrylic polymer binder functionalized with a quorum sensing inhibitor (QSI) belonging to the α-hydroxy γ-butenolide family. Unlike conventional biocides, QSIs are designed to interfere with bacterial communication involved in early biofilm formation rather than directly inhibit microbial growth. The selected QSI was synthesized by boron-catalyzed aldol lactonization, converted into a methacrylate monomer, and copolymerized with methyl methacrylate (MMA) by RAFT polymerization. The resulting PMMA-co-MMQSI copolymer contained 3 mol% of QSI-derived units and was formulated with rosin and pigments as a model antifouling paint. This binder design was intended to combine potential QSI availability during coating erosion with retention of a PMMA-rich acrylic matrix. The coating was evaluated for six months in flow-through aquaria supplied with natural seawater. Crystal violet staining showed significantly lower attached biomass on Paint-PMMA-co-MMQSI than on the non-functional PMMA reference. Under these aquarium conditions, the QSI-derived coating performed in the same range as the copper-containing formulation and the commercial reference Micron 350. Complementary bacterial biosensor assays demonstrated quorum sensing modulation by the Paint-PMMA-co-MMQSI leachate without inhibition of bacterial growth. These results provide a first proof of concept for a copper-free AF paint based on a QSI-functionalized acrylic binder. More broadly, the approach may be relevant to other water-exposed systems where persistent biofilm formation is problematic.