Structure–property relationship in AESO–vanillin copolymers: Effect of vinyl group position on polymer rigidity

Novel copolymers based on acrylate epoxidized soybean oil ( AESO ) and vinylic aromatic derivatives of vanillin ( VAV ) were synthesized and their thermal properties thoroughly evaluated. The study focused on bulk free-radical polymerization of AESO with two aromatic alkene isomers: one bearing a terminal vinyl group ( VAVE ) and the other featuring a central double bond ( VAVC ). This structural variation in the double bond position not only influenced the expected reactivity but also significantly affected the thermal properties of the resulting copolymers, synthesized at a 1:1 molar ratio of double bonds ( AESO:VAV ). The presence of acrylate groups in the soybean oil was confirmed via hydrogen nuclear magnetic resonance spectroscopy ( 1 H-NMR). Copolymerization was carried out using benzoyl peroxide as a free-radical initiator, yielding both soft and rigid polymeric materials. The mixtures were cured at 120°C for 9 h, followed by a post-curing step at 140°C for 1 h. The copolymers were characterized using Fourier-transform infrared spectroscopy (FTIR) to verify molecular structure, and their thermal behavior was assessed through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).