Kyu Ho Chae

Properties of 2,3-butanedione and 1-phenyl-1,2-propanedione as new photosensitizers for visible light cured dental resin composites

Abstract Two 1,2-diketones, 1-phenyl-1,2-propanedione (PD) and 2,3-butanedione (BD) were investigated as new visible light photosensitizers for formulating a dental resin composite of bis-GMA in order to improve the physical properties of the resin composite. The results were then compared with those of camphorquinone (CQ), the most widely used photosensitizer. Photodecomposition of the photosensitizers with and without amine was studied through UV absorption spectroscopy. The photopolymerization efficiency of bis-GMA containing the photosensitizer increased with irradiation time and with the amount of photosensitizer. The increase was in the order: BD

Melt free‐radical grafting of hindered phenol antioxidant onto polyethylene

A monomeric antioxidant (3) was prepared by reacting 3,5-di-tert-butyl-4-hydroxybenzyl alcohol (1) with N-[4-(chlorocarbonyl) phenyl] maleimide (2). This reactive antioxidant was grafted onto polyethylene (PE) by melt processing with free-radical initiators in a mini-max molder. The IR spectra of the grafted PE showed that the monomeric antioxidant was introduced onto the PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Also, the extent of crosslinking was indicated by the gel content. Grafting occurred in the following order: dicumyl peroxide (DCP) > benzoyl peroxide > 2,2′-azobisisobutyronitrile. The influences of the DCP concentration and monomeric antioxidant on the extent of grafting were studied. The effects of the reaction time and temperature were also determined.

Thermal curing reaction of poly(glycidyl methacrylate) using photogenerated amines from oxime-urethane derivatives

Two oxime-urethane derivatives, benzophenone oxime N-cyclohexylurethane (1) and dibenzophenone oxime N,N′-hexamethylenediurethane (2), were used as photobase generators. Photolysis of these derivatives results in the formation of amines which induce cross-linking of poly(glycidyl methacrylate) (PGMA) upon heating. The bifunctional derivative 2 is more efficient than the monofunctional derivative 1 in inducing thermal cross-linking of PGMA, with a maximum degree of insolubilization increasing up to ca. 90%.

Characterization of polyisoprene by temperature gradient interaction chromatography

Temperature gradient interaction chromatography (TGIC) analysis of polyisoprene (PI) is reported. PI can be fractionated in terms of molecular weight with high resolution by TGIC using a C18 bondedd silica column as the stationary phase and a mixture of CH 2 Cl 2 /CH 3 CN (80/20. v/v as the mobile phase. The temperature was increased during the elution from 5°C to 34°C to optimize the fractionation of high molecular weight PI. The relatively poor resolation in the low molecular weight range was improved by changing the eluent composition. For example, all the oligomeric species from the unimer to the 29mer of a low molecular weight PI (average mol. wt.: 900) were fully resolved with the mixed eluent of CH 2 Cl 2 / CH 3 CN (50/50, v/v) and a linear temperature program from 6°C to 40°C. In addition, simultaneons site exclusion chromatography and TGIC fractionation of PI/polystyrene, PI/poly(methylmethacrylate) mixtures are also reported.

Positive-Type Photosensitive Polyimide Based on a Photobase Generator Containing Oxime-Urethane Groups as a Photosensitive Compound

The chemical structure of a semi-aromatic polyimide-I, which was prepared by the chemical imidization of cyclopentanetetracarboxylic dianhydride and 2,2-bis(4-aminophenyl)hexafluoropropane, was characterized by13C-NMR spectroscopy. The chemically imidized polyimide-I was used for the preparation of a photosensitive polyimide (PSPI)|through the addition of benzophenone and benzophenone oxime hexamethylene diurethane (BOHD), a photobase generator containing oxime-urethane groups. The polyimide-I film containing benzophenone and BOHD was not soluble in 2.38 wt% tetrabutylammonium hydroxide solution in H2O. However, it became soluble following irradiation with 310 nm UV light. A positive tone image with a resolution of 5 μm was obtained with this PSPI, having sensitivity (Dc)|of 1.2 J/cm2 and contrast (γp)|of 1.08. Thus, a polyimide, which is not intrinsically photosensitive, can become photosensitive through the addition of a photobase generator containing oxime-urethane groups as a photosensitive compound.

Polymerization of N-[4-(azidocarbonyl)phenyl]maleimide and N-[4-(N′-phenoxycarbonylamino)phenyl]maleimide: polymers containing aromatic isocyanate precursors

Abstract N -[4-(Azidocarbonyl)phenyl]maleimide ( 3 ) and N -[4-( N ′-phenoxycarbonylamino)phenyl]maleimide ( 5 ) were polymerized and copolymerized with methyl methacrylate (MMA) or acrylic acid (AA) by initiation with AIBN. The resultant polymers were to have aromatic isocyanato groups when heated. In the differential scanning calorimetry measurement, the polymers from monomer 3 showed a strong and broad exotherm around 130°C. Thermogravimetric analysis also showed a weight decrease corresponding to the elimination of nitrogen at that temperature. The formation of isocyanato groups was confirmed by infra-red measurement with varying the cell temperature. The coupling reaction of the polymer with N -4-(nitrophenyl)- L -prolinol, resulting in the formation of urethane bonds, was carried out in a quantitative yield. The crosslinked films from copolymers of 5 and MMA or AA were obtained when heated above 200°C. The cured films were insoluble in common organic solvents. With the copolymers with AA it was expected that carboxylic groups would react with isocyanato groups generated from urethane units when heated. The copolymer was degraded above 150°C. After curing, its thermal stability improved dramatically, no weight loss being observed up to 300°C.

A one-component negative photoresist based on an epoxy terpolymer containing oxime-urethane groups as a photobase generator

For their application as one-component photoresists, we prepared epoxy terpolymers containing oxime-urethane and benzophenone groups by the radical polymerization of glycidyl methacrylate (GMA), methacryloxyethyl benzophenoneoxime urethane (MBU), andN-(4-benzoyl)phenylmaleimide (BPMI). The terpolymer composition was optimized to provide the most photosensitive photoresist. The photo-decomposition reaction of the oxime-urethane groups in the terpolymer was monitored by UV absorption spectroscopy, and the photo-crosslinking reaction of the epoxy terpolymer was observed by measuring the normalized thickness. The photosensitivity of the epoxy terpolymer increased as the amount of BPMI and MBU units increased up to 16 and 24 mol%, respectively. Among the terpolymers we prepared, terpolymer T-II(contents of GMA, MBU, BPMI are 75, 19, 6.1 mole%, respectively) exhibited the highest photosensitivity (Dc0.5=430mJ/cm2) and had a moderate contrast (γp = 1.23). Negative-tone micropatterns having a line width of ca. 10 μm were obtained by developing the system with chloroform.

Nanosecond laser flash photolysis study of 1,2-bispyrazylethylene

Abstract The nanosecond laser flash photolysis of 1,2-bispyrazylethylene indicates that an efficient intersystem crossing occurs on direct excitation. The triplet energy level of the trans isomer lies close to 39.0 kcal mol −1 and that of the cis isomer lies between 35.1 and 39.0 kcal mol −1 . The triplet-triplet absorption maximum of the trans isomer is blue shifted and the absorption spectra show fine structure because of the change of the energy gap between the 3 (n,π * ) and the lowest 3 (π,π * ) state as the polarity of the medium increases. The triplet lifetime of the trans isomer (160 ns) directly measured by laser flash photolysis also indicates that the direct photo-isomerization of this compound proceeds through the triplet manifold in contrast to the behaviour observed for stilbene.

Formation of various bicolor fluorescent micropatterns on a single polymer film based on concurrent photobleaching and photobase generation.

Various bicolored fluorescent micropatterns are fabricated on a single polymer film by concurrent photobleaching and a photobase generation process. A polymer, bearing anthracene and oxime-urethane groups, is dyed with rhodamine B isothiocyanate after irradiation with 310-nm UV light. The photochemical reaction of the polymer is monitored by UV, IR absorption, and fluorescence emission spectroscopy. Differently colored fluorescent micropatterns are obtained by selectively exciting each dye moiety. Various bicolored fluorescent micropatterns are observed through varying the excitation wavelength and observation wavelength ranges using a confocal microscope. This bicolored fluorescence patterning method will be useful to apply in photonic/electronic devices.

Fluorescence Micropatterning Based on the Polymeric Photobase Generator Containing Oxime-Urethane Groups by Dansylation

A polymeric photobase generator containing oxime-urethane groups is applied to a fluorescence micropatterning material. Polymer bearing oxime-urethane groups was prepared by copolymerization of methyl methacrylate with methacryloyloxyethyl benzophenoneoxime urethane (MBU). The reaction of amino groups in the irradiated copolymer film with dansyl chloride (Dns-Cl) was monitored by using UV absorption, IR absorption and fluorescence spectroscopy. The fluorescence spectrum of the Dns-Cl-treated irradiated copolymer film shows a strong fluorescence with a fluorescence maximum wavelength at 510 nm. A blue fluorescent micropattern with a line width of was obtained. Treatment of the irradiated copolymer film with Dns-Cl and rhodamine B mixture led to the formation of green, red, and orange-colored fluorescence micropatterns. Thus, various colored micropatterns on a single polymer film can be obtained by selective excitation of each dye molecules.