Synthesis and properties of UV-curable tung oil based resins via modification of Diels–Alder reaction, nonisocyanate polyurethane and acrylates

UV-curable tung oil based resins of GMA-PCDMAT and GMA-ICDMAT were synthesized via Diels–Alder reaction with maleic anhydride (MA), subsequent nonisocyanate polyurethane (NIPU) reaction with piperazine-1,4-dicarboxylic acid bis-(2-hydroxy-ethyl) ester (PCD) or isophoronediamine-1,4-dicarboxylic acid bis-(2-hydroxy-ethyl) ester (ICD) and acrylated modification with glycidyl methacrylate (GMA). The final chemical structures of GMA-PCDMAT and GMA-ICDMAT depend on the feeding ratio of MA, tung oil, PCD (or ICD) and GMA. Results of 1 H NMR and FTIR revealed that the targeted tung oil-based resins were successfully obtained. All the obtained resins had broad molecular weight distributions. UV-curing kinetic and thermal properties were respectively revealed by photo-DSC, DSC and TG. Higher concentration of C C bonds led to faster curing rate but lower final conversion of C C bonds. All the cured films had two glass transitions, one in the range of 8–10   °C and another in the range of 46–48   °C. All the cured films possessed excellent thermal stability, and the start temperature of decomposition ( T sta ) was as high as 350   °C, implying that they can be used for UV coatings for the substrates with high-temperature resistance. The introduction of structure of NIPU is helpful to enhance adhesion of the cured films with substrates.