Earticle

Polymerization of vinyl monomers is promoted by thianthrene cation radical as a part of our research concerning the reactions of various agents with readily isolable, yet highly reactive species and elucidate the biological activity. Thianthrene cation radical initiated the homopolymerization and copolymerization of styrene and ethyl vinyl ether. The polymerization yields decreased as the concentration of phenylacetylene or diphenylethylene increased. Such polymereization by cationic thianthrene radical could provide some clues for the reaction in living animals. Comments on possible polymerization mechanisms were suggested.

Bu3Sn-endded poly(vinyl)s with biological activity were obtained by the radical polymerization of vinyl monomers using thianthrene cation radical/nBu3H. Thianthrene cation and stannyl radicals promoted the homopolymerization and copolymerization of styrene and ethyl vinyl ether having number average molecular weights of 2000- 3100. Tributyltin hydride functions as a chain transfer agent. Such polymereization by cationic thianthrene and stannyl radicals could provide some clues for the biological reaction in living animals. Plausible polymerization mechanisms were suggested.

Oxocane high explosives substituted to explosive group such as azide (-CH2N3), nitrate (-CH2ONO2), and hydrazine (-CH2N2H3) are investigated theoretically the acid catalyzed reaction using the semiempirical MINDO/3, MNDO and AM1 methods to use as the guidelines of high explosives. The nucleophilicity and basicity of oxocane high explosives can be explained by the value of negative charge on oxygen atom of oxocane and the reactivity in propagation step can be represented by the value of positive charge on carbon atom and low electrophile LUMO energy. It was known that carbenium ion was favorable due to the stable energy (11.745~25.461 Kcal/mol) between oxonium ion and carbenium ion in the process of cyclic oxonium ion of oxocane high explosives being converted to open carbenium ion in oxocane high explosives. The value of concentration of cyclic oxonium ion and open carbenium ion in equilibrium status was found to be a major determinant of mechanism, it was expected to react faster in the prepolymer propagation step in SN1 mechanism than in that of SN2.

Oxepane high explosives substituted to explosive group such as azido, nitrato and hydrazino are investigated theoretically the acid catalyzed reaction using the semiempirical MINDO/3, MNDO and AM1 methods to use as the guidelines of high explosives. The nucleophilicity and basicity of oxepane high explosives can be explained by the value of negative charge on oxygen atom of oxepane and the reactivity in propagation step can be represented by the value of positive charge on carbon atom and low electrophile LUMO energy. It was known that carbenium ion was favorable due to the stable energy (19.507~32.101 Kcal/mol) between oxonium ion and carbenium ion in the process of cyclic oxonium ion of oxepane high explosives being converted to open carbenium ion in oxepane high explosives. The value of concentration of cyclic oxonium ion and open carbenium ion in equilibrium status was found to be a major determinant of mechanism, it was expected to react faster in the prepolymer propagation step in SN1 mechanism than in that of SN2.

As the development of nanotechnology, the use of composite resins which containing nanofillers becomes popular. The purpose of this study was to test the degree of polymerization of nanofillercontaining composite resins. For the study, three different nanofiller-containing composite resins and two different light-curing units were used. To evaluate the degree of polymerization, the maximum polymerization shrinkage taking place during the light curing, and the microhardness, after the light curing, were measured. As results, two light-curing units exhibited a similar emission spectrum to that of the included photoinitiator, camphorquinone. The only difference between the light-curing units were the width of the emission spectrum. Three different composite resins showed different microhardness values. Among them, Grandio showed the greatest microhardness value. However, there was less microhardness difference on the top and bottom surfaces due to the difference of the light-curing units. The maximum polymerization shrinkage values were also similar in the tested specimens regardless of the difference of the light-curing units. However, Grandio showed the least polymerization shrinkage. According to the manufacturers' data, Grandio showed the highest filler content(vol%).

Purpose: The aim of this study was to evaluate accuracy of three type complete mandibular denture of before and after polymerization. Methods: Mandibular edentulous model was selected as the master model. 15 study models were made by Type Ⅳ stone. Wax complete mandibular dentures were produced by the denture base and artificial teeth. Before and after curing, STL files were obtained using a blue scanner. By superimposing the digitized complete mandibular denture data(after curing) with the CAD-reference(before curing) three-dimensionally, visual fi t-discrepancies were drawn by calculating the root mean square (RMS) and visualized on a color-difference map. Each calculated RMS-value was statistically analyzed by 1-way analysis of variance(ANOVA) (α = .05). Results: Mean(SD) RMS-values was OM group 88.98(6.10)㎛, BM group 82.35(13.46)㎛, BDM group 77.83(9.46)㎛. The results of the 1-way ANOVA showed no statistically signifi cant differences in the RMS values of the Three groups for the material (P > .241). Conclusion : Deformation of artificial teeth position was observed in all groups after resin polymerization. But the values, all group were within the clinically acceptable range. The values of BDM group showed the least deformation than the other two groups.

Purpose: This study aimed to evaluate the effect of postcuring conditions, such as variations in light intensity and curing time, on the color stability of resins used in three-dimensional (3D)-printed dental restorations. Methods: Using an liquid crystal display 3D printer, 81 specimens in the shape of a 10.0 mm×1.5 mm disk were produced according to the specified parameters. The printed specimens were postcured at various light intensities (17.76, 121.43, and 199.99 mW/cm2) and curing times (5, 10, and 20 minutes). Color was assessed using a color difference spectrophotometer (CM-3600A, Konica Minolta) based on the Lab* color space defined by the International Commission on Illumination, and the L*, a*, b*, C*, and H values and ΔE00 were analyzed. To evaluate the effect of postcuring conditions on the color changes, a twoway analysis of variance was conducted. Tukey’s post hoc test (α=0.05) was performed to assess significant differences. Results: The results showed significant differences in L*, a*, and ΔE00 values based on light exposure and curing time (p<0.001), whereas b* and C* values differed significantly (p<0.05). H values were not significantly different (p=0.231). Conclusion: This study demonstrated that light exposure and curing time significantly influenced the color stability of 3D-printed resin restorations. Thus, light exposure of Lv7 or lower and curing times of ≤10 minutes are recommended for optimal color stability.

Purpose: This study is a mechanical strength supplementation of denture base resin Polymethyl methacrylate (PMMA) is in general use for denture base resin of the partial and full denture, however, The polymerization process of PMMA is not stabilized. Because of compatibility problems, preceding studies were performed, which were enhancing mechanical strength(Camilo Machado 2007),(Ana M. 2008), addition filler to materials property(Ayse Mese, 2008), self curing method(Hiroshi Shimizu, 2008). Methods: The carbon fiber and polyacetal filler, reinforced the mechanical strength for improving the stability of denture base resin were supplemented to the self cured resin. The Modulus of elasticity and the restoring force were calculated by tensile test. Results: The strengths of the heat and self cured resin were respectively decreased and increased, when the filler was supplemented to the denture base resin and the modulus of elasticity of both heat and self cured resin were not increased, when the filler was supplemented to the denture base resin. Conclusion: The restoring forces of self cured resin containing 10% filler were increased, when the filler was supplemented to the denture base resin.

Polyurethane resin containing isocyanate is marked by excellent tensile and mechanical strengths and this test aims to gauge its applicability as a medical high polymer. Tris [2-(acryloyloxy)ethyl]isocyanurate and hexamethylenediisocyanate were added to a basic mixing ratio of HEMA (2-hydroxyethyl methacrylate), MMA (methyl methacrylate), NVP (n-vinyl- 2-pyrrolidone) and crosslink agent, EGDMA (ethylene glycol dimethacrylate) with increasing proportions and copolymerized respectively. Also, the basic physical properties of the polymerized high polymers including refraction rate, tensile strength, light transmission and water content were measured to confirm that they are appropriate as hydrogelcontact lenses. After measuring the physical properties of high performance polymers produced by adding tris [2-(acryloyloxy) ethyl]isocyanurate, it was found that the average tensile strengths of sample TRIS1 to TRIS10 were between 0.285 and 0.612 kgf, while the average values of refractive index were ranged from 1.441 to 1.449 with water content from 30.00 to 37.35%.The measurement of physical properties of the copolymers generated by adding hexamethylenediisocyanate showed that the average tensile strength of sample HEXA1 to HEXA10 ranged from 0.267 to 1.742 kgf, the refractive index ranged from 1.443 to 1.475 and water contents were in the range of 21.22 to 35.58%. In all combinations the transmission rates satisfied the transmittance of general hydrogel contact lenses. From theresults, it is possible to conclude that the produced copolymers can be used as contact lens materials with excellent tensile strength.

This minireview provides the chosen examples of our recent discoveries in the polymerization of hydrosilanes, dihydrosilole, lactones, and vinyl derivatives using various catalysts. Hydrosilanes and lactones copolymerize to give poly(lactone-co-silane)s with Cp2MCl2/Red-Al (M = Ti, Zr, Hf) catalyst. Hydrosilanes (including dihydrosilole) reduce noble metal complexes (e.g., AgNO3, Ag2SO4, HAuCl4, H2PtCl6) to give nanoparticles along with silicon polymers such as polysilanes, polysilole, polysiloxanes (and silicas) depending on the reaction conditions. Interestingly, phenylsilane dehydrocoupled to polyphenylsilane in the inert nitrogen atmosphere while phenylsilane dehydrocoupled to silica in the ambient air atmosphere. Cp2M/CX4 (M = Fe, Co, Ni; X = Cl, Br, I) combination initiate the polymerization of vinyl monomers. In the photopolymerization of vinyl monomers using Cp2M/CCl4 (M = Fe, Co, Ni), the photopolymerization of MMA initiated by Cp2M/CCl4 (M = Fe, Co, Ni) shows while the polymerization yield decreases in the order Cp2Fe > Cp2Ni > Cp2Co, the molecular weight decreases in the order Cp2Co > Cp2Ni > Cp2Fe. For the photohomopolymerization and photocopolymerization of MA and AA, the similar trends were observed. The photopolymerizations are not living. Many exciting possibilities remain to be examined and some of them are demonstrated in the body of the minireview.

Hydrosilanes possessing reactive Si-H bond are used in synthesizing various types of polysilanes by dehydrocoupling under the influence of various organometallic promoters.42 Catalytic Si-Si/Si-O coupling of hydrosilanes with hydrosilanes, alcohols, and lactones to silicon-based polymers are described in this article as selective examples of our recent research developments. These silicon-containing polymers can be used as a precursor to prepare useful functional materials for fabricating electronic devices.

In this study, HEMA, MMA, AA, and EGDMA were used as basic combinations for manufacturing hydrophilic lenses for ophthalmic applications. In addition, AIBN (thermal polymerization initiator), 2H2M (photo polymerization initiator), and 3-hydroxypyridine (additive) were used to manufacture hydrophilic ophthalmic lenses through thermal polymerization and photo polymerization before their physical properties were measured. The results showed that when ophthalmic lenses were prepared via thermal polymerization and photo polymerization using 3-hydroxypyridine as an additive, their optical and physical properties and surface structures were different in each case, but they all satisfied the physical properties required for ophthalmic lenses.

본 연구에서는 고밀도 폴리에틸렌 제조공정에서 부산물로 생성되는 폴리에틸렌 왁스를 대상으로 무수말레인산을그라프트 반응 시킬 때, 반응 용매가 가지는 성질의 영향에 대해서 조사하였다. 측정결과, 자일렌이 톨루엔보다 우수한 모노머 용해성, 팽윤성, 혼화성을 가지며, 그라프트 반응을 더욱 촉진함을 알 수 있었고, 반응 용매의 함량에따라서는 0 ~ 200% v/w영역에서 200% v/w 조건이 최대의 그라프트 율을 보이고, 그이상의 용매가 사용될 경우에는 그라프트 율이 다시 감소하다가 일정해짐을 확인하였다. 가교도 함량 값은 용매 존재 하에 거의 생성되지 않았으며, 용매가 용매분자로 사슬이동반응 시켜 가교반응을 방지하는 것으로 판단되었다. 140oC에서 측정된 용융 점도값은 폴리에틸렌 왁스에 무수말레인산이 그라프트 된 후에 증가하는 경향을 보임을 알 수 있었다.

In this study, we have investigated the influence of the nature of solvent on the grafting reaction of maleic anhydride ontopolyethylene wax obtained as a by-product in a high density polyethylene plant. The results show that the grafting ratio in xyleneas a solvent was higher than toluene. This is because xylene has excellent monomer solubility, swelling property and miscibility. It has been also observed that grafting degree shows an initial jump in percentage of grafting with increasing amount of solvent,from 0% v/w to 200% v/w giving maximum grafting in 200% v/w and then slightly decreases on further increase in the amountof solvent and becomes almost constant. It can be also seen that gel content was not formed under the use of solvent. It meansthat solvent prevented cross-linking reaction due to chain transfer reactions to solvent molecules. Studies of melt viscosity at140oC showed that viscosity increased after grafting of maleic anhydride onto polyethylene wax.

Sodium alginate prepared from alginic acid was then graft copolymerized with acrylic acid monomer using hydrogen peroxide(H2O2) as an initiator, and the grafted copolymer was identified by IR spectroscopy method. When the amounts of sodium alginate, acrylic acid and hydrogen peroxide was kept constant in the reaction medium and then the contents of emulsifier was varied, SA conversion showed the maximum at the 3.0g of emulsifier and above that value it showed the downward trend. In the aqueous sodium alginate solution when the amounts of acrylic acid, hydrogen peroxide and emulsifier was remained constant and then the contents of sodium alginate was varied, AA conversion showed the maximum at the 15.0g of sodium alginate and above that value it showed the downward trend.

Purpose: The purpose of this study is to analyze the depth according to curing using photocurable resin for dental three-dimensional printing. Methods: A stainless mold with a height of 4 mm was prepared. Ultraviolet (UV) polymerization resin was injected into the mold. Photocuring was then performed for 5 minutes using a photopolymerizer, and the height was measured using a digital measuring instrument (first group). Second, light polymerization was also performed outside the mold for 5 minutes, and the height was measured using a digital measuring instrument. Third, light polymerization was further performed for 5 minutes, and the height was measured using a digital measuring instrument. Statistical analysis was performed with the Kruskal-Wallis test, which is a nonparametric test (α=0.05). Results: The third group had the largest measurement length, whereas the first group had the smallest. However, the difference between groups was not statistically significant (p>0.05). The color of the first group was different from that of the second and third groups. Conclusion: All of the 4-mm-thick photocured specimens had a curing reaction, but the part that was not directly irradiated with UV did not show its original color.

Surface sizing is one of the important process to the paper making. Surface sizing had an effect on penetration of oils, physical propertiesm water resistance for the paper. This study was carried out for the purpose of improving printability with surface sizing of domestic newspaper. The samples were prepared by means of TAPPI method(TAPPI 205 om~88), and were wested by IGT printability tester. The results of this study showed that the set-off was reduced on the surface sized with oxidized starch.

Among a large number of factors which influence the success of the overall lithographic process, the photoresist performance is a central one. Particularly, the polymer in a photoresist which undergo crosslinking or chain scission when irradiated with an energy such as UV, X-ray and electron beam, play key roles in the resist performance. Therefore, two most conventional photoresists, OMR-83 as a negative two component photoresist and AZ-1370 as a positive two component photoresist were chosen to study. After separation of base polymers from the resists by successive fractional fractional precipitation method, average molecular weight, molecular weight distribution, temperature(Tg), cyclicity and structure of base polymers were characterized

Purpose: In order to find out the impact of changes in polymerization conditions of orthodontic acrylic resin on maximum load. Methods: While maintaining mixing ratio 3:1 of polymer and monomer in spray-on way in the production condition of polymerization temperature 25℃ or 37℃ for 10 minutes or 30 minutes of polymerization time by pressure 3kfg/cm2 or 6kfg/cm2 in the lab maintaining 25℃ of room temperature, the change in maximum load rise rate was tested by producing 5 acrylic resin specimens for orthodontics per group to meet the standards of 25mmX 2mmX2mm and using INSTRON with the 3rd bar 2mm in diameter and parallel support bending device of 15 0.1 as test equipment showing 30.00mm/min of crosshead speed, 50±16 N/min of load ratio in the laboratory of 24℃ room temperature and as a result, the following results were obtained. Results: 1. When increasing pressure from 3kfg/cm2 to 6kfg/cm2, maximum load was lowered by -4.285%. 2. When increasing polymerization time from 10 minutes to 30 minutes, maximum load rose by 3.848%. 3. When increasing polymerization temperature from 27℃ to 37℃, maximum load rose by 5.854%. Conclusion: Considering the above test results that polymerization time and polymerization temperature when polymerizing acrylic resin for orthodontics according to changes in working conditions had an impact on the rate of rise of maximum load values but the rate of rise was lowered when increasing pressure from 3kfg/cm2 to 6kfg/cm2, we came to a conclusion that high pressure more than necessary does not affect the rate of rise of maximum load.

Purpose: The aim of this study is to evaluate composite resins of indirect restorations for testing of flexural strength according to various polymerization methods. Methods: Specimen was produced a total of 40 to 10 per each group with a length 25 mm, width 2 mm, thickness 2 mm using a Teflon zig. The polymerization groups were classified into four groups. The first group proceeded with light curing only(LC group). The second group proceeded with light and heat curing(LHC group). The third group proceeded with air press and light curing(ALC group). The fourth group proceeded with air press, light and heat curing(ALHC group). Each prepared group was evaluated by flexural strength test. Statistical analysis was performed by one-way ANOVA. Post-test was performed with Tukey test. Results: The lowest in the ALC group was 119.18 MPa and the highest in the ALHC group was 168.15 MPa. There were statistically significant differences. Conclusion : The composite resin of the indirect restoration is recommended to heat curing along with the air press.