• Journal of Adhesion and Interface
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• v.11 no.3
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• pp.112-119
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• 2010

Poly(methyl methacrylate)/poly(butyl acrylate) PMMA/PBA core-shell composite particles were prepared by the emulsion polymerization of MMA and BA in the presence of different concentration of sodium dodecyl benzene sulfonate (SDBS). The following conclusions are drawn from the measured conversion and particle size distribution, morphology, average molecular weight distribution, observation of film formation and particle formation, glass transition temperature and physical properties of polymerized core-shell composition particles for using adhesive binder. When the concentration of 0.03 wt% surfactant, the conversions of PMMA and PBA core polymerization are excellent as 95.8% for PMMA core and 92.3% for PBA core. Core-shell composite particles are obtained 90.0% for PMMA/PBA core-shell composite particles and 89.0% for PMMA/PBA core-shell composite particles. It is considered that the core and shell particles are polymerized to be confirmed FT-IR spectra and average molecular weight measured with a GPC, formation of the composite particles is confirmed by the film formation from normal temperature, and composition of inside and outside of the composite particle is confirmed by TEM photograph. The synthesized polymer has two glass transition temperatures, suggesting that the polymer is composed of core polymer and shell polymer unlike general copolymers. It is considered that each core-shell composite particle can be used as a high functionality adhesion binder by the measurement of tensile strength and elongation.

• Restorative Dentistry and Endodontics
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• v.23 no.2
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• pp.690-700
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• 1998

Rubber-toughened particles which are used in the field of chemical engineering are used to increase the fracture toughness of thermoset resin. The application of Core-Shell particles, one of rubber-toughened particles, as a filler for dental composite or restoration have not been examined. The purpose of this study was to evaluate possible use of Core-Shell particles for dental composite, and the hypothesis was that additional toughening mechanisms are activated by the addition of Core-Shell particles. After blending 50vol% quartz with Bis-GMA/TEGDMA resin matrix, the experimental resins were made by the addition of Core-Shell particles with varied content level as 0, 2.5, 5, 7.5, 10, 12.5, 15, and 20wt%. Fracture toughness was determined on three-point bending specimen with single-edge notch according to ASTM-E 399. Also, flexural properties, that is, strength and modulus were measured by three-point bending testing. Fractogragh of fracture toughness specimen was observed using SEM (JEOL 6400 SEM, MA). The following results from this study were obtained ; 1. Fracture toughness of composite resin added 2.5wt% Core-Shell particles was significantly higher than control group ($p{\leq}0.05$). 2. Flexural properties were decreased with increasing Core-Shell particle content, which showed a correlation statistically ($p{\leq}0.05$). 3. A toughening mechanism such as lamination and microcrack was observed in specimen determined high fracture toughness. 4. The dispersion of Core-Shell itself and quartz filler particles was limited present high content of Core-Shell particles, which decreased a resulting mechanical properties of composites. These results suggest that adequate Core-Shell particles can be used to enhance mechanical properties included toughening for dental composites.

• Macromolecular Research
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• v.9 no.1
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• pp.51-65
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• 2001

Two-stage emulsion polymerizations of hydrophobic monomers on hydrophilic seed polymer particles were carried out to make core-shell composite particles. It was found that the loci of polymerization in the second stage were the surface layer of the hydrophilic seed latex particles, and that it has resulted in the formation of either eccentric core-shell particles with the core exposed to the aqueous phase or aggregated nonspherical composite particles with the shell attached on the seed surface as many small separated particles. The driving force of these phenomena is related to the gain in free energy of the system in going from the hydrophobic polymer-water interface to hydrophilic polymer-water interface. Thermodynamic analysis of the present polymerization system, which was based on spreading coefficients, supported the likely occurrence of such nonspherical particles due to the combined effects of interfacial free energies and phase separation between the two polymer phases. A hypothetical pathway was proposed to prepare hydrophilic core-hydrophobic shell composite latex particles, which is based on the concept of opposing driving and resistance forces for the phase migration. It was found that the viscosity of the monomer-swollen polymer phase played important role in the formation of particle morphology.

• Journal of the Korean Applied Science and Technology
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• v.26 no.1
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• pp.74-79
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• 2009

The inorganic-organic composite particles with core-shell structure were polymerized by using styrene and potassium persulfate (KPS) as a shell monomer and an initiator, respectively. We studied the effect of surfactants on the core-shell structure of silicone dioxide/styrene composite particles polymerized in the presence of sodium dodecyl sulfate(SDS), polyoxyethylene alkylether sulfate (EU-S133D), and at none surfactant condition. We found that $SiO_2$ core / polystyrene(PS) shell structure was formed when polymerization of styrene was conducted on the surface of $SiO_2$ particles, and the concentration SDS and EU-Sl33D was $8.34{\times}10^{-2}mole/L$. The core-shell structure was confirmed by measuring the thermal decomposition of the polymer composite using thermogravimetric analyzer (TGA), and the morphology of the composite particles was characterized by transmission electron microscope (TEM).

• Journal of Adhesion and Interface
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• v.14 no.1
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• pp.1-12
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• 2013

Multi core-shell composite particles were prepared by the water-born emulsion polymerization of various core monomers such as methyl methacrylate (MMA), ethyl methacrylate (EMA) and shell monomers such as MMA, EMA, 2-hydroxyl ethyl methacrylate (2-HEMA), glycidyl methacrylate (GMA) and methacrylic acid (MAA) in the presence of different concentrations of sodium dodecyl benzene sulfonate (SDBS). The following conclusions are drawn from the conversion, particle size and distribution, average molecular weight, molecular structure, glass transition temperature with DSC, contact angle after plasma treatment, tensile strength and isothermal decomposition kinetics. In the case of the concentration of 0.02 wt% SDBS, the conversion of MMA core-(EMA/GMA) shell composite particles was excellent as 98.5%. In the case of the concentration of 0.03 wt% SDBS, the particle size of EMA core-(MMA/GMA) shell composite particles was high as $0.48{\mu}m$. We confirmed that 3 points of glass transition temperatures appear for multi core-shell composite particles compared to 1~2 points of glass transition temperatures appear for general copolymer particles. Overall, the adhesion strength of shell composite particles was in the order of EMA/MAA > EMA/2-HEMA > EMA/GMA.

• Journal of the Korean Applied Science and Technology
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• v.20 no.1
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• pp.27-32
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• 2003

The core-shell latex particles were prepared by sequential emulsion polymerization of alkyl methacrylate and styrene(ST) by using an water-soluble initiator(APS) after preparing monomer pre-emulsion in the presence of an anionic surfactant(SDBS). In organic/organic core-shell polymerization, the pre-emulsion method, which minimized required quantity of sulfactant, has been used to increase the conversion rate and the stability of core-shell latex particles as well as to reduce the formation of secondary particle that cause problems of soap-free emulsion during shell polymerization. We used several methods to observe the core-shell structure. The core-shell structure was studied by measuring pH change during hydrolysis by NaOH, glass transition temperature($T_g$) by differential scanning calorimeter(DSC), morphology of latex by transmission electron microscope(TEM) and change of particle size and distribution by a particle analyzer.

• Journal of Powder Materials
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• v.17 no.4
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• pp.295-301
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• 2010

Multi shell graphite coated Ag nano particles with core/shell structure were successfully synthesized by pulsed wire evaporation (PWE) method. Ar and $CH_4$ (10 vol.%) gases were mixed in chamber, which played a role of carrier gas and reaction gas, respectively. Graphite layers on the surface of silver nano particles were coated indiscretely. However, the graphite layers are detached, when the particles are heated up to $250^{\circ}C$ in the air atmosphere. In contrast, the graphite coated layer was stable under Ar and $N_2$ atmosphere, though the core/shell structured particles were heated up to $800^{\circ}C$. The presence of graphite coated layer prevent agglomeration of nanoparticles during heat treatment. The dispersion stability of the carbon coated Ag nanoparticles was higher than those of pure Ag nanoparticles.

• Applied Chemistry for Engineering
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• v.25 no.5
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• pp.526-530
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• 2014

Polystyrene-poly(etheramic acid) core-shell particles were prepared by dispersion polymerization of styrene using poly(etheramic acid) obtained by the reaction of 2,2'-bis[4-(3,4-dicarboxyphenoxy) phenyl]propane dianhydride and 3,5-diamniobenzoic acid as a stabilizer. 4-Vinylbenzyltrimethylammonium chloride was used as a comonomer to increase the binding efficiency of poly(etheramic acid). When the ethanol-water mixture (7 : 3) was used as a reaction medium, particles were stabilized well and the size distribution of particles was fairly narrow. The particle size increased with the amount of styrene. The particles polymerized in the dimethylformamide-water mixture had a broad size range. Polystyrene-poly(etheramic acid) core-shell particles were transformed to polystyrene-polyetherimide core-shell particles by the chemical imidization of shells.

• Korean Journal of Materials Research
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• v.20 no.12
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• pp.691-698
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• 2010

Magnesium hydroxide-melamine core-shell particles were prepared through the coating of melamine monomer on the surface of magnesium hydroxide in the presence of phosphoric acid. The melamine monomer was dissolved in hot water but recrystallized on the surface of magnesium hydroxide by quenching to room temperature in the presence of phosphoric acid. The core-shell particle was applied to low-density polyethylene/ ethylene vinyl acetate (LDPE/EVA) resin by melt-compounding at $180^{\circ}C$ as flame retardant. The effect of magnesium hydroxide and melamine content has been studied on the flame retardancy of the core-shell particles in LDPE/EVA resin according to the preparation process and purity of magnesium hydroxide. Magnesium hydroxide prepared with sodium hydroxide rather than with ammonia solution revealed higher flame retardancy in core-shell particles with LDPE/EVA resin. At 50 wt% loading of flame retardant, core-shell particles revealed higher flame retardancy compared to that of the exclusive magnesium hydroxide in LDPE/EVA composite, and it was possible to satisfy the V0 grade in the UL-94 vertical test. The synergistic flame retardant effect of magnesium hydroxide and melamine core-shell particles was explained as being due to the endothermic decomposition of magnesium hydroxide and melamine, which was followed by the evolution of water from the magnesium hydroxide and porous char formation due to reactive nitrogen compounds, and carbon dioxide generated from melamine.

• Journal of the Korean Applied Science and Technology
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• v.25 no.3
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• pp.404-409
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• 2008

The core-shell composite particles of inorganic/organic were polymerized by using styrene(St) as a shell monomer and potassium persulfate (KPS) as an initiator. We studied the effect of core-shell structure of silicone dioxide/styrene in the presence of an anionic surfactant sodium lauryl sulfate (SLS) and polyoxyethylene alky lether sulfate (EU-S133D). We found that when $SiO_2$ core/PSt shell polymerization was prepared on the surface $SiO_2$ particle, to minimize the coagulation during the shell polymerization, the optimum conditions were at concentration of $2.56{\times}10^{-2}mole/L$ SLS. The structure of core-shell polymer was confirmed by measuring the thermal decomposition of polymer composite using thermogravimetric analyzer and morphology of core-shell polymer particles by transmission electron microscope (TEM).