Fabrication of Tri‐Layered Core‐Shell Structure Acrylonitrile–Styrene–Acrylate ( <scp>ASA</scp> ) Particles for Toughening Poly(Styrene‐Co‐Acrylonitrile) Resin

ABSTRACT Tri‐layered ASA core–shell toughening particles with controlled grafting ratios were synthesized to simultaneously improve the mechanical properties of poly(styrene‐co‐acrylonitrile) (SAN). Poly(butyl acrylate) (PBA) cores with different grafting agent distributions were synthesized via semicontinuous emulsion polymerization. ASA particles were then prepared by the grafting emulsion polymerization at different conditions. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) revealed particle sizes of 395–471 nm, uniform dispersion, and stable morphology. Samples with a moderate grafting ratio (11.5%) exhibited the best property balance, with 11.5 kJ/m 2 impact strength, 15% elongation at break, and a Vicat softening point of 101.2°C. At 0.15% t‐dodecyl mercaptan (TDDM) loading, rubber cores achieved optimal flexibility and stability, yielding the highest toughness. Incorporating 10% methyl methacrylate (MMA) increased the grafting ratio to 15.2%, improving whiteness (66%), brightness (91.3%), gloss (83.6%), and tensile strength (54 MPa); the toughening ability of ASA particles was limited when the grafting ratio reached certain levels. These findings demonstrate that controlling the tri‐layer core–shell architecture, TDDM concentration, and MMA fraction allows for simultaneous optimization of toughness, thermal stability, and surface properties in ASA resins.