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51. Synthesis of acid anhydride‐modified flexible epoxy resins and enhancement of impact resistance in the epoxy composites.

Author

Kim, Hye Jin, Kim, Hyeon‐Gook, Seo, Bongkuk, and Lim, Choong‐Sun

Subjects
EPOXY resins, POLYURETHANES, IMPACT strength, POLYMERS, BRITTLENESS
Abstract

Epoxy resins are key materials used in various applications, including coatings, adhesives, and composites. Tougheners, such as nanoparticles, soft polymers, elastomeric polyurethanes, and core/shell particles, have been widely applied to compensate for the brittleness of the epoxy matrix and to enhance the impact resistance. Modifying epoxy resin by reacting it with a flexible component is one of the representative methods to overcome the weakness of cured epoxy polymers upon impact. For introducing flexible parts, we synthesized three types of epoxy‐modified resins by reacting acid anhydride with glycidol, followed by reaction with bisphenol [F, S, or J] glycidyl ether to produce flexible modified epoxy resins. Mechanical tests, such as flexural strength and impact resistance tests, were performed by adding various amounts of the synthesized resin to the epoxy composites. The results of these tests suggest that the modified resins were effective in improving the toughness of the epoxy matrix. [ABSTRACT FROM AUTHOR]

Published
2023
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54. Photoelectrochemical Epoxidation of Cyclohexene on an α-Fe2O3Photoanode Using Water as the Oxygen Source

Author

Tayebi, Meysam, Masoumi, Zohreh, Tayyebi, Ahmad, Kim, Jun-Hwan, Lee, Hyungwoo, Seo, Bongkuk, Lim, Choong-Sun, and Kim, Hyeon-Gook

Abstract

This study developed a safe and sustainable route for the epoxidation of cyclohexene using water as the source of oxygen at room temperature and ambient pressure. Here, we optimized the cyclohexene concentration, volume of solvent/water (CH3CN, H2O), time, and potential on the photoelectrochemical (PEC) cyclohexene oxidation reaction of the α-Fe2O3photoanode. The α-Fe2O3photoanode epoxidized cyclohexene to cyclohexene oxide with a 72.4 ± 3.6% yield and a 35.2 ± 1.6% Faradaic efficiency of 0.37 V vs Fc/Fc+(0.8 VAg/AgCl) under 100 mW cm–2. Furthermore, the irradiation of light (PEC) decreased the applied voltage of the electrochemical cell oxidation process by 0.47 V. This work supplies an energy-saving and environment-benign approach for producing value-added chemicals coupled with solar fuel generation. Epoxidation with green solvents via PEC methods has a high potential for different oxidation reactions of value-added and fine chemicals.

Published
2023
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62. Synthesis of isoeugenol biobased epoxy polymer by forming α‐hydroxyl ester and degradation studies.

Author

Sivanesan, Dharmalingam, Seo, Bongkuk, Lim, Choong‐Sun, Song, Jinyoung, and Kim, Hyeon‐Gook

Subjects
EPOXY resins, POLYMERS, GLASS transition temperature, ESTERS, DIAMINODIPHENYLMETHANE, PLANT biomass
Abstract

The synthesis of bio‐based monomers and polymers from renewable feedstock, such as plant biomass, is desirable because of the depletion of fossil fuel resources and the reliance of thermosetting epoxy resin on non‐renewable petrochemical monomers. Despite the excellent polymeric properties of bisphenol‐based epoxy resins, these negatively impact human health. Herein, the synthesis of self‐curable epoxy polymers from the bio‐based material isoeugenol by forming α‐hydroxyl esters is reported. The epoxides are named AB (single epoxide and ester groups) and A2B2 (double epoxide and ester groups), based on the number of active ester and epoxide groups. The materials derived from the bio‐based material, AB and A2B2, were initiated with and without the catalyst N,N′‐dimethylaminopyridine (DMAP) and curing agent diaminodiphenylmethane. Without the catalyst, AB and A2B2 self‐polymerized at 247 and 210°C, respectively. Notably, the polymerization temperatures for AB and A2B2 decreased after the addition of DMAP. The self‐cured epoxy resin without the catalyst showed the highest thermal stability and glass transition temperature (Tg = 156°C). Degradation and recovery studies suggested forward that 51% of the material could be recovered and 94% of the polymer could be degraded from the self‐cured A2B2 in 25 wt% NaOH solution. [ABSTRACT FROM AUTHOR]

Published
2022
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75. Metal- and halide-free solid-type multifunctional alkanolamines as catalysts for cycloaddition of CO2.

Author

Kim, Hyeon-Gook, Son, Hye Jeong, and Lim, Choong-Sun

Abstract

Although the production of cyclic carbonates from CO2 and epoxides can be promoted by eco-friendly halogen- and metal-free organic catalysts, its homogeneity complicates the catalyst reuse. Herein, we synthesized solid multifunctional alkanolamines using simple epoxy and amine reactions, and analyzed their structures by IR and 13C-NMR. Then, we employed these as catalysts for CO2 cycloaddition with propylene oxide, obtaining propylene carbonate in 98% yield after 3 h at 120 °C. Moreover, at 60 °C, the reaction was successfully repeated five times and a product yield of 50% was maintained throughout. [ABSTRACT FROM AUTHOR]

Published
2019
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76. Panchromatic Photon-Harvesting by Hole-Conducting Materials in Inorganic–Organic Heterojunction Sensitized-Solar Cell through the Formation of Nanostructured Electron Channels

Author

Chang, Jeong Ah, Im, Sang Hyuk, Lee, Yong Hui, Kim, Hi-jung, Lim, Choong-Sun, Heo, Jin Hyuk, and Seok, Sang Il

Abstract

Additional photon-harvesting by hole transporting materials in Sb2S3-sensitized solar cell is demonstrated through the formation of electron channels in the hole transporter such as P3HT (poly(3-hexylthiophene)) and PCPDTBT(poly(2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)) that can act as both a hole conductor and light absorber. As a result, the short-circuit current density is improved with an increment in overall efficiency. These findings provide new insights into use of light-absorbing conjugated polymers as a hole conductor in the inorganic–organic heterojunction sensitized solar cells.

Published
2024
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77. Thermodynamics of Core Metal Replacement and Self-Assembly of Ca2+15-Metallacrown-5†

Author

Tegoni, Matteo, Furlotti, Michele, Tropiano, Manuel, Lim, Choong Sun, and Pecoraro, Vincent L.

Abstract

The equilibria for coreCa2+replacement by Ln3+in copper(II) 15-MC-5 complexes have been investigated using a series of visible spectrophotometric titrations of calcium(II) metallacrowns ({CaII[15-MCCuII(N)(L)-5]}2+) with Ln3+ions (H2L = pheha, (S)-α-phenylalaninehydroxamic acid, or trpha, (S)-α-tryptophanhydroxamic acid). These studies allowed the determination of the equilibrium constants for the reaction {CaII[15-MCCuII(N)(L)-5]}2++ Ln3+→ {LnIII[15-MCCuII(N)(L)-5]}3++ Ca2+in methanol/water 9:1 (Ln3+= La3+, Gd3+, Dy3+, Er3+) or 99:1 (Ln3+= La3+, Nd3+, Gd3+, Dy3+, Er3+, Yb3+), respectively. The log Kfor these reactions decreases with increasing atomic number of the lanthanide(III), ranging from 6.1 to 3.91 in methanol/water 9:1. The same behavior is observed in methanol/water 99:1, although the constants are uniformly lower (log K= 4.09−2.52). A significant thermodynamic selectivity was observed for the later lanthanides (Gd3+−Yb3+) while a smaller selectivity is present throughout the beginning of the series (La3+−Gd3+). This observation has been interpreted on the basis of the size correspondence between the metal ions and the metallacrown cavity. The overall stability of the {CaII[15-MCCuII(N)(L)-5]}2+in methanol/water 9:1 has been determined by pH-spectrophotometric titrations with HCl. The resulting log Kvalues are 63.46(12) and 65.05(13) for pheha and trpha, respectively (Ca2++ 5Cu2++ 5HL−= {CaII[15-MCCuII(N)(L)-5]}2++5H+). The stability of both the La3+and Ca2+15-metallacrown-5 complexes in the presence of high Na+concentrations has also been demonstrated by spectophotometric studies. Based upon these observations, the preference of the 15-MC-5 for Ca2+complexation compared to crown ethers has been quantitatively demonstrated for the first time.

Published
2024
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78. Metal-Dependent Phase Selection in Coordination Polymers Derived from a C2v-Symmetric Tricarboxylate

Author

Lim, Choong-Sun, Schnobrich, Jennifer K., Wong-Foy, Antek G., and Matzger, Adam J.

Abstract

Reacting biphenyl-3,4′,5-tricarboxylic acid (H3BHTC) with the appropriate metal salt yields the microporous coordination polymers (MCPs) Mn3(BHTC)2(1), Mg3(BHTC)2(2), and Co3(BHTC)2(3) containing hourglass metal clusters. The addition of Cu to reactions with CoII, FeIII, or MnIIleads to the formation of heterobimetallic UMCM-150 isostructural analogues Co1Cu2(BHTC)2(4), Fe1Cu2(BHTC)2(5), and Mn1Cu2(BHTC)2(6) containing both paddlewheel and trinuclear metal clusters. X-ray diffraction analysis of the crystals of the heterobimetallic MCPs suggests that Cu on the trinuclear site of UMCM-150 was replaced by the other metal, whereas Cu in paddlewheel sites remains unchanged. N2sorption isotherms were measured for the mixed-metal UMCM-150 analogues, and it was confirmed that there is no structural collapse after the metal replacement.

Published
2024
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85. Chiral Metallacrown Supramolecular Compartments that Template Nanochannels: Self-Assembly and Guest Absorption

Author

Department of Chemistry, Willard H. Dow Laboratories, The University of Michigan, Ann Arbor, MI 48109-1055 (USA), Fax: (+1)???734-647-4865, Lim, Choong-Sun, Jankolovits, Joseph, Kampf, Jeff W., Pecoraro, Vincent L., Department of Chemistry, Willard H. Dow Laboratories, The University of Michigan, Ann Arbor, MI 48109-1055 (USA), Fax: (+1)???734-647-4865, Lim, Choong-Sun, Jankolovits, Joseph, Kampf, Jeff W., and Pecoraro, Vincent L.

Abstract

No Abstract

Published
2010

86. Cover Picture: Chiral Metallacrown Supramolecular Compartments that Template Nanochannels: Self-Assembly and Guest Absorption (Chem. Asian J. 1/2010)

Author

Department of Chemistry, Willard H. Dow Laboratories, The University of Michigan, Ann Arbor, MI 48109-1055 (USA), Fax: (+1) 734-647-4865, Lim, Choong-Sun, Jankolovits, Joseph, Kampf, Jeff W., Pecoraro, Vincent L., Department of Chemistry, Willard H. Dow Laboratories, The University of Michigan, Ann Arbor, MI 48109-1055 (USA), Fax: (+1) 734-647-4865, Lim, Choong-Sun, Jankolovits, Joseph, Kampf, Jeff W., and Pecoraro, Vincent L.

Abstract

No Abstract

Published
2010

88. Efficient inorganic–organic hybrid heterojunction solar cells containing perovskite compound and polymeric hole conductors

Author

Heo, Jin Hyuck, primary, Im, Sang Hyuk, additional, Noh, Jun Hong, additional, Mandal, Tarak N., additional, Lim, Choong-Sun, additional, Chang, Jeong Ah, additional, Lee, Yong Hui, additional, Kim, Hi-jung, additional, Sarkar, Arpita, additional, Nazeeruddin, Md. K., additional, Grätzel, Michael, additional, and Seok, Sang Il, additional

Published
2013
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