Colorless, Highly Transparent, and UV-Resistant Waterborne Polyurethanes Achieved by Introducing Bio-Based Methyl Syringate

Abstract To address the limitations of traditional UV-protective materials regarding optical transparency and long-term weatherability, this work successfully synthesized a UV-absorbing functional monomer (PMSMA-OH) derived from bio-based methyl syringate. By integrating it with polytetramethylene ether glycol (PTMEG) as co-soft segments via in-situ polymerization, a series of modified waterborne polyurethanes (MWPUs) featuring intrinsic anti-UV capabilities was developed. The optimal MWPU-5% system achieves an impeccable structure–property balance, not only sustaining a transmittance of over 96% in the visible light region but also exhibiting strong characteristic absorption against 200–300 nm UV radiation. Benefiting from its stable molecular network, the material's tensile strength (22.31 MPa) and elongation at break (674.52%) exhibited no significant deterioration following 72 h of accelerated UV aging. Simultaneously, a water contact angle of 95° and excellent cytocompatibility further broaden its prospective application scenarios. When applied as a functional coating for automotive glass, it delivers a UV-shielding efficiency of up to 97% without any color distortion. Ultimately, this material system demonstrates immense potential for engineering translation, offering an effective and sustainable solution for advanced optical and skin-friendly protective coatings.