Bio-based polyfunctional reactive diluent derived from tung oil by thiol-ene click reaction for high bio-content UV-LED curable coatings

Materials with high bio-content have gradually replaced petroleum-based materials due to their sustainability, low cost, low toxicity and excellent performance in the field of UV-LED curable coatings. A novel tung oil-based methacrylate (TDMM) with low viscosity and multiple photopolymerizable methacrylates was designed and synthesized through three steps containing amidation, thiol-ene click reaction and esterification. The reaction conditions for thiol-ene click reaction were optimized by calculating double bond conversion and degree of functionalization of polyols. The chemical structures of the as-prepared TDMM were characterized by 1 H NMR and FTIR. The rheological behavior analysis indicated that TDMM exhibited lower viscosity than petrochemical-based reactive diluent pentaerythritol triacrylate (PETA). Subsequently, TDMM showed good copolymerization ability with soybean oil-based reactive monomer (AESO) under the “green + green” UV-LED curable systems with high bio-content (61–81% in theory). The TDMM/AESO systems showed higher T g but lower thermal stability, better modulus and tensile strength than the neat AESO. Besides, the UV-LED cured coatings exhibited excellent physical and chemical properties. This bio-renewable tung oil-based monomer is shown to be an effective reactive diluent and considered to have good potential in the development of the UV-LED curable coatings.