Phenyl-Containing Silicone–Acrylate Core–Shell Particles for Transparent Toughening of PMMA with Enhanced Property Retention Under UVA Aging

Transparent toughening of poly(methyl methacrylate) (PMMA) requires simultaneous control of mechanical energy dissipation and optical scattering, together with retention of properties under ultraviolet exposure. Here, silicone–acrylate (Si–ACR) core–shell particles comprising a PHSO-derived silicone-rich core and a PMMA-rich outer region were prepared by two-stage seeded emulsion polymerization without a deliberately added grafting agent. The phenyl-containing silicone-rich phase was selected to reduce the anticipated refractive-index contrast with PMMA. Si–ACR particles with an average diameter of 275 nm provided a favorable mechanical–optical balance. At 15 wt% Si–ACR, the notched Izod impact strength increased from 1.8 to 18.1 kJ/m², while total luminous transmittance remained 91.4% and 90.8% for 1 and 2 mm specimens, respectively, with haze below 0.8%. Fracture morphology was consistent with local debonding and/or void formation followed by enhanced plastic deformation of the PMMA matrix. After 500 h of accelerated UVA exposure, the blend retained an impact strength of 16.8 kJ/m² and a transmittance of 89.7% for the 1 mm specimen. These findings suggest potential applications in transparent protective shields and optical covers requiring improved impact resistance, low haze, and property retention under UVA exposure.