Synthesis and characterization of eco-friendly siloxane-semifluorinated polyurethane coatings for underwater application Anthony Yesudass Sebastin , Smita Mohanty, Sanjay K. Nayak Laboratory for Advanced Research in Polymeric Materials, Central Institute of Plastics Engineering & Technology, B-25, CNI Complex, Patia, Bhubaneswar 751024, Odisha, India Correspondence to: A. Y. Sebastin (E-mail: anthonyyds@gmail.com) ABSTRACT: Siloxane-semifluorinated polyurethane coatings were prepared for robust underwater application. Initially, acrylic polyol (FS-GPTACP)-containing fluoroalkoxysilane (1H,1H,2H,2H-Perfluorooctyltrimethoxysilane) pendant group was synthesized by the free-radical polymerization method. Different weight percentages of polydimethylsiloxane (0, 10, and 20 wt %) were added to the polyol to tune the mechanical and the surface energy of the coating. Subsequently, this polyol mixture was cured with 4, 4 0 -methylenebis(cyclo- hexyl isocyanate) (H 12 MDI) to prepare a series of siloxane-semifluorinated polyurethane–urea hybrid coatings (APUS 0%, APUS 10%, and APUS 20%). The synthesized coating showed low surface energy, hydrophobicity with exceptional water, and alkali resistance. Moreover, the coating displayed excellent mechanical properties with low pseudobarnacle adhesion strength. The coatings also showed nontoxicity against gram-positive and gram-negative bacterial strains. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47720. KEYWORDS: alkoxysilane; foul-release coatings; polydimethylsiloxane; polyurethane Received 13 November 2018; accepted 16 February 2019 DOI: 10.1002/app.47720 INTRODUCTION Underwater coatings’ application ranges from ship hull 1 to bio- sensors. 2 More particularly, slime and biofilm formation on the submerged structure has a serious impact on economic and envi- ronmental viewpoints. Especially, fouled marine vessels often decrease maneuverability and freight capacity, resulting in increased greenhouse gas emission, fuel consumption, time, and cost. 3,4 To overcome this setback, antifouling surface was made, which limits and/or weakens intermolecular interaction or hydro- gen bonding between biomolecules and the man-made surface. 5 For coatings, two main strategies have been used: one is the anti- fouling approach wherein the attachment of the fouling organism to the surface is restricted 6 and another technology is foul-release coatings, which releases the accumulated fouling species by hydrodynamic shear force. 7 In the earlier days, antifouling coat- ings appeared to be an ideal solution, which was bestowed with self-polishing antifouling paints that contain tributyltin (TBT). However, these coatings were restricted globally after being used for several decades due to the presence of toxic biocides, such as TBT, and its adverse issue with nontargeted marine livings. 8 Copper-containing antifouling paint also had some negative impact on the marine environment. 9 Therefore, these drawbacks have diverted researchers toward the development of foul-release coating framework, due to its nontoxic character. 10,11 Further, the surface properties such as low surface energy, 12 low porosity, 13 low modulus 14 and high molecular mobility, which helps to control the foul settlement and enhances the foul releasing properties of the surface. Hence, the adhesion of the fouling organisms to the coating surface was relatively weak, which can be easily wiped by applying water jet or increasing ship speed. Moreover, these coatings exhibited bet- ter chemical and physical stabilities in seawater. 15 Generally, silicone-based materials, such as polydimethylsiloxane (PDMS), are being used in the commercial foul-release coatings, due to their low elastic modulus, low surface energy, low glass transition temperature (T g ), and good chemical resistance. 16 The flip side of this material exhibits poor mechanical properties. In order to enhance their mechanical properties, typically PDMS is rein- forced with large quantities of inorganic fillers or is being chemi- cally bonded with other polymer systems. For instance, Pieper et al. 17 synthesized crosslinked PDMS-polyurethane foul-release coatings; Sommer et al. 18 developed pigmented siloxane–polyure- thane coatings; and Galhenage et al. 11 synthesized silicone oil- modified siloxane-polyurethane foul-release coatings. These coat- ings showed low force in the pseudobarnacle detachment, along with an easy release of Navicula incerta, Ulva liza, and Balanus amphitrite syn. Amphibalanus amphitrite. In another report, T. P. Galhenage and coworkers investigated the foul-release perfor- mance of polyethylene glycol-modified amphiphilic siloxane © 2019 Wiley Periodicals, Inc. 47720 (1 of 11) J. APPL. POLYM. SCI. 2019, DOI: 10.1002/APP.47720