Preparation of the flexible soybean oil-based material via [2 + 2] cycloaddition photo-polymerization

Polymers with high flexibility and high content renewable biomass materials have attracted particular attention. Plant-derived trans-cinnamic acid (CA) was introduced into the structure of epoxidized soybean oil to form trans-cinnamated epoxidized soybean oil (ESOCA). ESOCA with multi-cinnamate groups was cured via [2 + 2] cycloaddition photo-polymerization that with no need of photoinitiator, while acrylated epoxidized soybean oil (ESOAA) was photocured via free radical photopolymerization for comparison. The successful synthesis of ESOCA and ESOAA resin was proved by Fourier transform infrared, proton nuclear magnetic resonance, and gel permeation chromatography results. ESOCA is more environmentally friendly than ESOAA for that trans-CA volatility is much lower than acrylic acid during synthesis process. Notably, UV-cured ESOCA samples had a higher tensile strength at break and a 14.75 times elongation at break of that of UV-cured ESOAA samples, showing that [2 + 2] cycloaddition photo-polymerization is a good strategy to prepare flexible materials. Performances of ESOCA as coating on flexible PET film were also better than those of ESOAA, especially the flexibility, adhesion, and UV shielding performance. This study may open up a new way for design and synthesize flexible high performance polymer from renewable biomass materials.