Influence of Diol Structure on the Mechanical and Thermal Properties of Bio-Based UV-Curable Unsaturated Polyesters for 3D Printing

A series of high bio-based unsaturated polyester resins (UPRs) were synthesized using itaconic acid (IA) and various diols─including linear, branched, and aromatic types─to investigate the influence of molecular structure on the thermal and mechanical performance of UV-cured systems. The prepolymers were prepared via melt polycondensation and subsequently cured under 405 nm UV light using styrene as the reactive diluent and (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (TPO) as the photoinitiator. UPR-IE (ethylene glycol-based) among linear diols, achieved the highest tensile strength (43.33 MPa). In the branched group, the symmetrical UPR-IMPr exhibited the best impact resistance (1.73 kJ/m2), while UPR-I8D2E containing 20% dimethyl terephthalate (DMT) demonstrated outstanding tensile strength (51.85 MPa) and elongation (13.47%). Thermogravimetric analysis (TGA) confirmed that all of the samples exhibited thermal stability above 200 °C (Td-5%). Selected UPRs were successfully printed using UV-based three-dimensional (3D) printing, demonstrating their great potential as sustainability-enabling materials for photopolymer-based 3D fabrication.