![]() The core–shell impact modifiers consist a soft crosslinked rubber core and a hard shell grafted onto the rubber. In the core–shell morphology, the second-stage polymer forms a shell around the seed polymer. Many parameters such as the type and amount of surfactant, reaction temperature, crosslinking of the seed polymer and hydrophobicity of the monomers and polymers control the particle morphology (Sundberg et al., 1990 Stubbs and Sundberg, 2004, 2008 Jonsson et al., 1991 Durant and Sundberg, 1996 Chen et al., 1991). Composite latex particles, containing two or more different polymers, generally made by emulsion polymerization, can be used as impact modifier. One of the most successful methods developed for modifying plastics is the blending of specially designed and preformed impact modifiers into the matrix (Gui et al., 2010 Lee and Chang, 2004 Cho et al., 2005 Abreu et al., 2005). Crosslinking dimethacrylate monomers which commonly used as the matrix of dental composites suffer from some drawbacks such as brittleness and poor resistance to crack initiation and propagation due to their densely crosslinked molecular structure (Manhart et al., 2000 Singh et al., 2002 Du and Zheng, 2007). Usually the organic matrix of dental composites is based on methacrylate monomers. Recently composite materials for tooth restoration are finding widespread application. This study shows that incorporation of proper amount of hybrid core-shell particles in dental composites can improve their fracture toughness and thus may extend their service life. The results of mechanical tests showed that fracture toughness of Bis-GMA/TEGDMA dental resins improved about 35% by the inclusion of 5 wt% silica-loaded core-shell hybrid particles with little effect on flexural strength. Formation of glassy shell on PBA core in core-shell particles, grafting of ɣ -MPS onto the silica particles and encapsulation of modified silica by polymeric shell in core-shell hybrid particles were confirmed using various analytical techniques. Mechanical properties (fracture toughness, flexural strength and flexural modulus) of the photo-cured Bis-GMA/TEGDMA dental resins/composites filled with different mass fractions of synthesized nanoparticles were tested, and analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. The morphology of core-shell particles was examined by SEM/TEM. Afterwards, polymeric shell was coated on silica nanoparticles through emulsion polymerization. Then the surface of silica particles was treated with ɣ-MPS. ![]() For preparing the core-shell hybrid particles, first silica particles with diameters of about 68 nm were synthesized based on the Stöber process. Core-shell particles consisting of polybutyl acrylate (PBA) rubbery core and polymethyl methacrylate (PMMA)/polystyrene (PS) shell were synthesized by seeded emulsion polymerization. Also this work examined the influence of synthesized nanoparticles loading in a Bis-GMA/TEGDMA resin matrix on some mechanical properties of the dental composite resins. The aim of this study was to synthesize acrylic core-shell particles and silica-loaded core-shell hybrid particles through emulsion polymerization.
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