Effective Studies of bio-derived free radical polymerizable hydroxyl functional macromonomer for replacement of Hydroxylethyl Methacrylate (HEMA) in acrylic polyols and their polyurethane-urea coatings

The present work aims to study the impact of replacing HEMA monomer with a bio-based free radical hydroxyl functional macromonomer derived from castor oil (CO) in the synthesis of acrylic polyols. It also evaluates the coating properties of the resulting polyurethanes (PUs) in comparison to conventional acrylic polyols (AP-HEMA) derived from HEMA. To achieve this, castor oil was first reacted with maleic anhydride (MA) to produce the castor oil-derived free radical polymerizable hydroxyl functional macromonomer (COMA). Subsequently, castor oil-based acrylic hybrid polyols were synthesized using acrylate monomers, specifically methyl methacrylate (MMA) and butyl acrylate (BA), along with varying weight percentages of COMA through a conventional radical copolymerization process. The successful replacement of HEMA with COMA in the acrylic polymerization was verified through Fourier transform infrared (FTIR) spectroscopy, hydroxyl value analysis, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). The acrylic hybrid polyols derived from castor oil exhibited reduced viscosity, lower glass transition temperature (Tg), and decreased molecular weight compared to AP-HEMA. Both castor oil based, and AP-HEMA based acrylic polyols were further reacted with Isophorone diisocyanate (IPDI) at an OH: NCO ratio of 1:1.6 to form isocyanate-terminated polyurethane prepolymers. The Tg of the castor oil-based acrylic hybrid polyurethane coating films was found to be lower than that of petroleum-derived HEMA based acrylic polyols, demonstrating enhanced performance in terms of contact angle, water resistance, flexibility, adhesion, and abrasion resistance. The overall findings highlight the feasibility of using castor oil-derived COMA as a sustainable alternative in acrylic polyol formulations. The bio-derived free radical polymerizable hydroxyl functionality exhibits polymerization tendency within the conventional acrylic polymerization framework, indicating its potential as a substitute for the HEMA monomer in the synthesis of acrylic polyols, thereby yielding high solid content resins suitable for high-performance polyurethane coating applications.