• Restorative Dentistry and Endodontics
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• v.39 no.4
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• pp.310-318
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• 2014

Objectives: This study examined the influence of the resin thickness on the polymerization of silorane- and methacrylate-based composites. Materials and Methods: One silorane-based (Filtek P90, 3M ESPE) and two methacrylate-based (Filtek Z250 and Z350, 3M ESPE) composite resins were used. The number of photons were detected using a photodiode detector at the different thicknesses (thickness, 1, 2 and 3 mm) specimens. The microhardness of the top and bottom surfaces was measured (n = 15) using a Vickers hardness with 200 gf load and 15 sec dwell time conditions. The degree of conversion (DC) of the specimens was determined using Fourier transform infrared spectroscopy (FTIR). Scratched powder of each top and bottom surface of the specimen dissolved in ethanol for transmission FTIR spectroscopy. The refractive index was measured using a Abbe-type refractometer. To measure the polymerization shrinkage, a linometer was used. The results were analyzed using two-way ANOVA and Tukey's test at p < 0.05 level. Results: The silorane-based resin composite showed the lowest filler content and light attenuation among the specimens. P90 showed the highest values in the DC and the lowest microhardness at all depth. In the polymerization shrinkage, P90 showed a significantly lower shrinkage than the rest two resin products (p < 0.05). P90 showed a significantly lower refractive index than the remaining two resin products (p < 0.05). Conclusions: DC, microhardness, polymerization rate and refractive index linearly decreased as specimen thickness linearly increased. P90 showed much less polymerization shrinkage compared to other specimens. P90, even though achieved the highest DC, showed the lowest microhardness and refractive index.

• Restorative Dentistry and Endodontics
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• v.32 no.1
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• pp.28-36
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• 2007

The purpose of this study was to compare the effect of exponential curing method with conventional curing and soft start curing method on polymerization shrinkage of composite resins. Three brands of composite resins (Synergy Duo Shade, Z250, Filtek Supreme) and three brands of light curing units (Spectrum 800, Elipar Highlight, Elipar Trilight) were used. 40 seconds curing time was given. The shrinkage was measured using linometer for 90 seconds. The effect of time on polymerization shrinkage was analysed by one-way ANOVA and the effect of curing modes and materials on polymerization shrinkage at the time of 90s were analysed by two-way ANOVA. The shrinkage ratios at the time of 20s to 90s were taken and analysed the same way. The results were as follows : 1. All the groups except Supreme shrank almost within 20s Supreme cured by soft start and exponential curing had no further shrinkage after 30s (p < 0.05). 2. Statistical analysis revealed that polymerization shrinkage varied among materials (p = 0.000) and curing modes (p = 0.003). There was no significant interaction between material and curing mode. 3. The groups cured by exponential curing showed the statistically lower polymerization shrinkage at 90s than the groups cured by conventional curing and soft start curing (p < 0.05). 4. The initial shrinkage ratios of soft start and exponential curing were statistically lower than conventional curing (p < 0.05). From this study, the use of low initial light intensities may reduce the polymerization rate and, as a result, reduce the stress of polymerization shrinkage.

• Journal of Pharmaceutical Investigation
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• v.40 no.2
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• pp.73-78
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• 2010

Hydrogels are thought to be a promising delivery carrier for protein drugs because of their favorable aqueous environment compared with nano/micro-particles of hydrophobic polymer such as PLGA. In this study, nano-sized hydrogels (nanogels) were fabricated using inverse-miniemulsion polymerization method. The mean size of nanogels in range of 90-160nm and affected by the preparation parameters such as sonication time and concentration of monomer. While longer sonication time and lower concentration of acrylamide monomer showed a tendency to produce smaller nanogels and to have lower lysozyme activity, variation of bis-methylene acrylamide concentration made no difference. Although both longer soncaton time and lower acrylamide concentration increased in vitro release rate, acrylamide concentration was more effectively affected to the control of protein release rate, which indicated that the release rate of protein from nanogels affected by not only their size but also internal structure. In conclusion, nanogels prepared by inverse-miniemulsion can be a useful carrier for application of protein drug, because of simple process, minimum contact of organic solvent and high protein activity.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.4
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• pp.833-849
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• 1996

The material of choice for functional and esthetic reconstruction of maxillofacial defects is silicone. Silicone has appropriate physical properties for maxillofacial prosthesis but it has weak edge strength. Therefore, a proper combination of silicone and polyurethane sheet is recommended to improve this weakness. Various primers are also used to enhance the adhesive strength between silicone and polyurethane sheet. The purpose of this study was to determine the adhesive strength of silicone and polyurethane sheet. Silicone elastomer mixture was made by admixing MDX4-4210 elastomer (40%) and Silastic Medical Adhesive Type A(60%). This silicone elastomer mixture was attached to polyurethane sheet, using one of three different primers(1205, S-2260, or A-304), treated for 1, 2, 4, 6, and 8 hours. These were then polymerized in room temperature, dry-heat oven or microwave oven. Six specimens per each group, a total of 270 specimens were prepared for final test. The differences of T-peel bonding strengths were then determined by a test. The differences of T-peel bonding strengths were then determined by a test method that was recommended by American Society for Testing and Materials C794-80. The results were statistically analyzed using the ANOVA and Mutiple Range Tests(Tukey' HSD). The reults were as follow. 1. Type of primer, primer reaction time, and methods of polymerization showed significant correlation on the T-peel bonding strengths in adhesiveness between silicone and polyurethane sheet. 2. A-304 primer showed statistically higher in T-peel bonding strength than otehr type of primers except for the polymerization in microwave oven with reaction times of 2, 6 hours(p<0.05). 3. No significant differences in T-peel bonding strength were observed among the polymerization methods. 4. The effect of reaction time by the primer type and polymerization method showed statistically significant differences in bonding strength among different reaction times. And in most cases, reaction time of 1 or 2 hours showed higher T-peel bonding strength.

• Journal of the korean academy of Pediatric Dentistry
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• v.46 no.4
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• pp.392-399
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• 2019

The purpose of this study was to evaluate polymerization of TheraCal LC, one of the tricalcium silicate cements. To measure the Vickers hardness number (VHN), the specimens were cured at different light curing time and distance. As a result, the VHN of the upper surface was significantly higher than the lower surface's in all groups (p < 0.05). The VHN of the lower surface was increased significantly with the increase of the light curing time in all distance (p < 0.05). When the distance was more than 4.0 mm at all light curing time, the VHN of lower surface was significantly decreased (p < 0.05). When the specimen was light cured for 20 seconds, the VHN of the lower surface did not exceed 2, which corresponds to 10% of the upper surface's. These results suggested that the 20 second light curing time was not sufficient to polymerize the lower surface under specific conditions and that light-curing time should be increased.

• Journal of the Korean Chemical Society
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• v.27 no.1
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• pp.66-72
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• 1983

Anionic polymerization of 2-pyrrolidone was carried out by TDI (Toluene Diisocyanate)/KOH catalysis. The effects of TDI / KOH mole ratio, KOH concentration, temperature and time on polymerization were investigated. It was observed that the highest rate of polymerization and maximum conversion were obtained when TDI / KOH mole ratio was about 0.25. The maximum conversion and the highest viscosity were obtained when the concentration of KOH was 5 mole percent. It was also found that the rate of polymerization and inherent viscosity at $30^{\circ}C$ were higher than those at $50^{\circ}C$. The rate constant ($k_p$) of polymerization was determined by least square method; the values of kp obtained were $57.53{\ell}/mole{\cdot}min\;at\;30^{\circ}C$ and $52.36{\ell}/mole{\cdot}min\;at\;50^{\circ}C$, respectively.

• Applied Chemistry for Engineering
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• v.10 no.6
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• pp.902-906
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• 1999

Electrically conducting composite films were prepared by a vapor phase in situ polymerization of pyrrole in the methyl cellulose film containing a copper(II) perchlorate. Methylcellulose had high affinity to pyrrole and was used as a matrix polymer. Conducting polypyrrole was embedded in the methylcellulose film forming a conducting network and the conductivity of the composite films ranged $10^{-1}$ to $10^{-7}S/cm$. The conductivities of conducting composite films were dependent on the nature of the matrix polymers, concentration of oxidant and polymerization time. In situ polymerization of pyrrole was observed in the matrix polymer and confirmed by UV-vis spectra. From the results of the thermogravimetric analysis, the chemical oxidative polymerization of pyrrole in the matrix polymers did not give any negative effects on the thermal stability of the composite films. Electron micrograph of composites indicated good penetration of PPy in the matrix polymer. DMA suggested a certain degree of incompatibility of the polypyrrole in the composites.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1444-1446
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• 2009

The atmospheric pressure plasma polymerization of acrylate monomers was carried out to have dielectrics with easy preparation and high performance. The effects of discharge power, monomer concentration and deposition time on film properties were investigated using various characterization tools. With proper conditions, smooth dielectric layer of 100nm thickness was obtained. Dielectric property as organic dielectric layer has been studied for future applications in organic thin film transistors(OTFT).

• Journal of Industrial Technology
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• v.25 no.A
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• pp.141-149
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• 2005

We investigated numerically the evolutions of several chemical species which are important for film growth and particle generation in the pulsed $SiH_4$ plasmas. During the plasma-on, the $SiH_x$ concentration increases with time mainly by the generation reaction from $SiH_4$, but, during the plasma-off, decreases because of the hydrogen adsorption reaction. During the plasma-on, the concentrations of negative ions increase with time by the polymerization reactions of negative ions and those become almost zero in the sheath regions because of the electrostatic repulsion. During the plasma-off, the concentrations of negative ions decrease with time by the neutralization reactions with positive ions and some negative ions can diffuse toward the sheath regions because there is no electric field inside the reactor. The polymerized negative ions of higher mass can be reduced successfully by using the pulsed plasma process.

• Proceedings of the Korean Magnetic Resonance Society Conference
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• 2000.08a
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• pp.1-1
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• 2000