This paper investigates the structural modifications of castor oil, a renewable resource, to develop functional organic inorganic hybrid coatings. A novel methodology has been developed to introduce hydrolyzable −Si−OCH 3 groups in the castor oil backbone that has been used subsequently for the development of polyurethane/urea−silica hybrid coatings. The alkoxysilane functional castor oil (ASCO) was characterized by techniques such as 1 H, 13 C, and 29 Si nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The ASCO was further reacted with different ratios of isophorone diisocyanate (IPDI) to get an isocyanate-terminated hybrid polyurethane prepolymer that was cured under atmospheric moisture to get the desired coating films. The glass transition temperatures (Tg) of the hybrid networks were found to be in the range of 29−70 °C, and the water contact angles were in the range of 75°−82°. The Tg and hydrophobic character of the hybrid coating films found to increase with an increasing NCO/OH ratio. The thermo-mechanical, viscoelastic, swelling, morphological, and contact angle properties of these films were evaluated. The alkoxy silane-modified castor oil-based coatings have shown better mechanical and viscoelastic properties in comparison to the control (unmodified castor oil) coatings. This work provides an effective and promising way to prepare hydrolyzable silane functional castor oil for high performance hybrid coatings.
A series of novel waterborne hyperbranched polyurethane-urea (WHBPU) were prepared with different chain extenders (diamine, diol, and siloxane) by a systematic reaction process. Initially, the hyperbranched polyester polyol was prepared by reacting polytetramethyleneglycol (PTMG)-1000 with 2,2-bis(hydroxymethyl) propionic acid (DMPA) in a molar ratio of 1:14 (3rd generation) at 160 °C by one pot synthesis. This was reacted with an adduct of isophorone diisocyanate (IPDI) and DMPA with NCO:OH mole ratio of 1.6:1. Then 50% of free NCO in these prepolymers was reacted with three different chain extenders (diol, diamine and APTES). This reaction mixture was neutralized with triethyl amine and another 50% of free NCO was chain extended with isophorone diamine during water dispersion. The obtained polyester was characterized with Fourier transform-infrared spectroscopy (FT-IR), 1 H and 13 C NMR, respectively. The properties of WHBPU and their hybrid coatings were studied by FT-IR, 1 H NMR, thermogravimetric analyzer (TGA), dynamic mechanical, and thermal analyzer (DMTA), and the contact angle measurement. TGA and DMTA results confirmed that these coatings have good thermal and mechanical properties. The onset degradation temperature of the WHBPU without APTES starts in between 200 and 250 °C, whereas the APTES chain extended WHBPU starts at 250 °C. T g of WHBPU without APTES varies between 106 and 126 °C, while 129 °C for APTES chain extended WHBPU. The conditions for the reproducible preparation of suitable products have been found and optimized. They enable the tuning of their properties according to the intended use. The aim of the prepared WHBPU films is long-term use as thermal and mechanical resistant systems. Along with these property APTES crosslinked system, the hydrophobic silica-rich surface is likely to be inhibited the hybrid films upon exposure to an aqueous environment.
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