Design and Characterization of Silane-Modified Bio-Based Non-Isocyanate Polyurethane Coatings for Advanced Surface Applications

Non-isocyanate polyurethanes (NIPUs) represent a sustainable alternative to conventional isocyanate-based systems, eliminating toxic reagents while maintaining good performance. In this study, bio-based NIPU coatings were synthesized from carbonated soybean oil (CSBO) via the carbonation of epoxidized soybean oil (ESBO) using carbon dioxide (CO2), followed by polymerization with ethylenediamine (EDA) and varying concentrations of 3-aminopropyltriethoxysilane (APTES) (0–20 wt%). The amine groups of EDA and APTES participate in the ring-opening of cyclic carbonates to form β-hydroxyurethane linkages, while the triethoxysilane moieties of APTES may undergo hydrolysis–condensation to produce Si–O–Si domains, resulting in a β-hydroxyurethane–siloxane hybrid network. The optimized formulation CEA-5 exhibited the best, including a tensile strength of 3.3 MPa, elongation at break of ~150%, glass transition temperature (Tg) of ~7 °C, and thermal stability up to ~350 °C, where major thermal degradation happens. The synthesized coating material also shows adhesion (3.6 MPa on oak for CEA-10), hydrophobic behavior (water contact angle (WCA) ~102° for CEA-5), good chemical and ultraviolet (UV) resistance, and shape memory. The synergistic effect of urethane hydrogen bonding and siloxane crosslinking imparted enhanced toughness, flexibility, and durability. These findings express a scalable, eco-friendly strategy for producing silane-modified NIPU coatings with good mechanical, thermal, and coating performance suitable for sustainable industrial coating and adhesive applications.