Preparation and Characterization of Fluorinated Hydrophobic UV-Crosslinkable Thiol-Ene Polyurethane Coatings
The polyurethane prepolymer terminated with a double bond was synthesized using isophorone diisocyanate (IPDI), hydroxyl terminated polybutadiene (HTPB), 1,4-butanediol (BDO), and 2-hydroxyethyl acrylate (HEA). Then, a series of innovative UV-curable polyurethane coatings were prepared by blending ene-terminated polyurethane, fluoroacrylate monomer, and multifunctional thiol crosslinker upon UV exposure. The incorporation of fluoroacrylate monomer and multifunctional thiols into polyurethane
... nto polyurethane coatings significantly enhanced the hydrophobic property, mechanical property, pencil hardness, and glossiness of the polyurethane coatings. This method of preparing UV crosslinkable, hydrophobic polyurethane coatings based on thiol-ene chemistry exhibited numerous advantages over other UV photocuring systems. Coatings 2017, 7, 117 2 of 12 of their structure versatility, environmental friendliness, and terrific mechanical properties    . The method of urethane-fluoroacrylate UV photopolymerization is another way to obtain fluorinated polyurethane. Çakmakçı et al.  prepared fluorine-containing photocurable hybrid coatings with thiol-ene click reaction and a sol-gel technique. 3-mercaptopropyltrimethoxysilane (MPTMS) was used as a coupling agent, and perfluorooctyltriethoxysilane (PFOTES) was used to introduce fluorine. The addition of fluorine and silica improved the mechanical property, flame retardancy, hydrophobicity, and oleophobicity of the coatings. A similar study was also conducted by Mackey et al.  . They prepared a series of organosilicate hydrolyzable monomers combined with trimethylolpropane tris (3-mercaptopropionate) (tri-thiol) in a thiol-ene "click" polymerization reaction to produce clear, colorless thiol-ene networks using radiation and thermal-cure techniques. Reinelt et al. synthesized oligomers based on innovative thiol derivative 4a for the production of low-odor and low-shrinkage thiol-ene dental composites, which showed good mechanical properties and reduced shrinkage stress  . In this work, the polyurethane prepolymer resins terminated with a double bond were synthesized. Then, a series of UV-curable polyurethane coatings were prepared. To improve the hydrophobicity of the coatings, (N-ethylperfluorooctylsulfonamido) methyl acrylate (EFCSA) was introduced by way of photo-initiated polymerization. Differing from the conventional method of preparing fluorinated polyurethane films, pentaerythritol tetra (3-mercaptopropionate) (PETMP) was further added to accelerate the polymerization rate and improve the reaction depth of the UV-curable polyurethane coatings based on a thiol-ene click reaction. The mechanical property, hydrophobicity, gel yield, pencil hardness, glossiness, and water absorption of the coatings were tailored by varying the contents of EFCSA and PETMP. The significance of this study lies in introducing a thiol-ene click crosslinking system for the fabrication of polyurethane coatings, which resulted in the advantages of high curing speed, low energy consumption, and improved yellowing resistance. This method could be easily achieved in the industrial application of UV-curable films.