Synthesis and Performance Study of Self‐Crosslinking Styrene‐Acrylate Emulsion Based on Vegetable Oil

ABSTRACT A core‐shell PA/ESO@ASR styrene‐acrylate emulsion was synthesized and characterized, in which epoxidized soybean oil (ESO) and a styrene‐acrylate copolymer (PA) are physically confined in the particle core and an alkali‐soluble resin (ASR) forms the shell. A green self‐crosslinking strategy was achieved through a thermally induced epoxy‐carboxyl ring‐opening addition reaction. Mini‐emulsion polymerization was carried out from an ultrasonicated preemulsion of ESO, styrene, methyl methacrylate, and butyl acrylate. The influence of ESO loading (0–30 wt%) and the carboxyl to epoxy groups molar ratio ( R = 0.8, 1.0, 1.2) on emulsion stability, particle size, film formation, and postcure thermal/mechanical properties was examined. FT‐IR monitoring shows progressive attenuation of the epoxy and ASR carbonyl bands, consistent with epoxy‐carboxyl ring‐opening esterification during thermal cure. DSC indicates that curing is effectively completed at 140°C, with the fastest cure and highest conversion at moderate ESO loadings (≈20–25 wt%) and R ≈ 1. Cured films exhibit substantially increased hardness and strong adhesion while retaining moderate toughness at intermediate ESO content. TGA reveals that ASR raises high‐temperature stability, whereas excessive ESO lowers the decomposition onset temperature. The combined “physical encapsulation + thermally triggered self‐crosslinking” approach affords a balanced, low‐VOC route to bio‐based waterborne coatings.