Functional polyurethane–urea coatings from sulfur rich hyperbranched polymers and an evaluation of their anticorrosion and optical properties

Abstract

The study showcases functional polyurethane–urea coatings from sulfur rich hyperbranched polyols. A multistep synthetic route was used that can be easily adopted as a one pot approach towards generating (i) new monomers, (ii) hyperbranched macromonomers, (iii) reactive pre-polymers and (iv) functional polymeric architectures with exotic properties. Thiol–yne click chemistry was successfully employed to synthesize a trihydroxy terminated sulfur-core monomer (B₃), which was reacted with succinic anhydride to achieve an acid terminated monomer, A₃. Following an A₃ + B₃ approach, these complementary pairs led to the formation of a generation-1 sulfur rich hyperbranched polyol. Achieving higher generation via repetitive steps is demonstrated with the formation of generation-2 polyols. The targeted monomers, intermediates and polyols were confirmed using ¹H-NMR, ¹³C-NMR, ESI-MS/MALDI-ToF, and mid-FTIR techniques. The degree of branching, ∼86.4 and 84.4% for the generation 1 and 2 hyperbranched polyols respectively, indicated highly branched systems. The rheology data from these hyperbranched polyols established their suitability for processing and application development. Isocyanate terminated prepolymers were derived from these polyols through reaction with a diisocyanate, and, when moisture cured, yielded high quality polyurethane–urea films/coatings. Comprehensive evaluation of the morphologies using FE-SEM, and thermo-mechanical and optical properties (refractive index 1.5, %T > 90) revealed the interesting features of the coatings. Moreover, a salt spray (more than 1500 hours of stability) and electrochemical tests (corrosion rates 4.2 × 10⁻⁴ and 6.3 × 10⁻⁴ mm per year) of the developed coatings emphasized their excellence in protecting against corrosion. Additionally, these additive-free films displayed significant inhibition towards microbes.