Ng Siu Choon
Email Address
chmngsc@nus.edu.sg
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Publication Morphology of microporous polymeric materials by polymerization of methyl methacrylate and 2-hydroxyethyl methacrylate in microemulsions(1995-05) Chieng, T.H.; Gan, L.M.; Chew, C.H.; Ng, S.C.; CHEMISTRYA microemulsion system consisting of methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA) and a crosslinking agent, ethylene glycol dimethacrylate, in water using sodium dodecyl sulfate as a surface-active agent was investigated. A study on the phase behaviour of the system was conducted to determine the type of microstructures that may be present. Polymerization was carried out at room temperature using dibenzyl ketone as a photoinitiator. The morphology (microstructure) of the resulting polymeric materials was found to depend strongly on the composition (water content, surfactant content, and MMA to HEMA ratio) of the precursor microemulsions. © 1995.Publication Blue electroluminescence from a novel donor/acceptor polymer structure(2000-08-02) Ng, S.-C.; Lu, H.-F.; Chan, H.S.O.; Fujii, A.; Laga, T.; Yoshino, K.; CHEMISTRYThe synthesis and properties of novel series of soluble donor/acceptor conjugated polymers composed of dioctyloxy-substituted phenylene and pyridine units are presented. The derived polymers gave strong blue emission in their solution and film states, with very high quantum yields in CHCl3 solution. Polymers with metalinkages showed blue-shifts in their UV, PL and EL spectra. Blue-emitting single layer LED devices were successfully fabricated from these polymers and gave blue light.Publication Preparation of M41S family mesoporous silica thin films on porous oxides(2005-07-05) Huang, L.; Kawi, S.; Hidajat, K.; Ng, S.C.; CHEMISTRY; CHEMICAL & BIOMOLECULAR ENGINEERINGThe preparation of thin films of silicate MCM-41 and silicate MCM-48 on porous oxides have been studied using spin-coating, hydrothermal deposition, X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption and thermogravimetry (TG). The work has included the template removal conducted on both supported thin films and powder samples via supercritical fluid extraction (SFE) at 85 °C and calcination at 540 °C. XRD and SEM observations show that films of both mesoporous molecular sieves are synthesized on the substrates with cetyltrimethylammonium bromide (CTMABr)-tetraethyl orthosilicate (TEOS) gels and beneficially formed on the substrates with pore sizes of 0.15 μm upwards. XRD and N2 adsorption-desorption studies reveal that removing the template via calcination leads to mesoporous structural distortion of supported MCM-41 and large pore contraction of supported MCM-48 thin films, whereas removing the template via SFE results in stable supported thin films with uniform mesopores. TG analysis indicates that the template SFE efficiency attains to 78% upwards. The behavior of supported thin films and powder samples in synthesis and in template removal are compared. The effects of the substrate on the formation and structural stability of thin films are observed. © 2005 Elsevier Inc. All rights reserved.Publication Novel efficient blue fluorescent polymers comprising alternating phenylene pyridine repeat units: Their syntheses, characterization, and optical properties(2001-09-25) Ng, S.-C.; Lu, H.-F.; Chan, H.S.O.; Fujii, A.; Laga, T.; Yoshino, K.; CHEMISTRYA novel series of poly(2,5-dialkoxy-1,4-phenylene-alt-2,5-pyridine)s functionalized with alternating donor/accepter repeat units was synthesized using a Suzuki coupling approach and characterized by FT-IR, NMR (13C and 1H), UV-vis, fluorescence spectroscopy, gel permeation chromatography, and thermal analyses. The derived polymers were soluble in common organic solvents and trifloroacetic acid and exhibited good thermal stability. In all cases, the electronic and optical properties of these novel copolymers were consistent with the rigid-rod conjugated structure. They emitted intense blue light under UV irradiation in both the film and solution phases with high quantum yields. Single-layer blue light-emitting diodes were successfully fabricated using these materials as emitting layers. The electrochemical behavior of these new polymers depicted facile n-doping and good electron transporting properties attributable to the presence of the electron-withdrawing pyridinyl unit. These polymers displayed bathochromic shift when protonated with trifluoroacetic acid in chloroform solutions. The surface morphologies of the polymer films cast from chloroform and chloroform/trifloroacetic acid mixtures were investigated by scanning electron micrographs.Publication Thermal decomposition of methylated γ-thiobutyrolactones: A photoelectron spectroscopic study(1996-04) Chua, Y.T.; Mok, C.Y.; Huang, H.H.; Novak, I.; Ng, S.C.; CHEMISTRYThe thermal decomposition of γ-thiovalerolactone, α-methyl-γ-thiobutyrolactone and β-methyl-γ- thiobutyrolactone has been studied in a gaseous flow system, by monitoring the changes in the photoelectron spectra recorded during the course of the reactions. Three modes of decomposition were observed, two involve loss of carbon monoxide (decarbonylation) and one involves loss of carbonyl sulfide (decarboxylation). The decarbonylation reaction producing an olefin and a thioaldehyde and the decarboxylation producing an olefin are similar to those observed for the unsubstituted thiobutyrolactone. The third reaction, observed only in the methylated compounds, is decarbonylation with the formation of hydrogen sulfide and butadiene. It is proposed that the last reaction can be attributed to the relatively facile elimination reaction of a butenethiol intermediate.Publication Synthesis of electrically conducting poly{2,2′-[5,5′-(1,2-ethynediyl)] bisthiophene}(1996-04-15) Ng, S.C.; Chan, H.S.O.; Leong, L.S.; Sarkar, A.; CHEMISTRYPublication The in vitro Antitumour Activity of Substituted Dibutyl-1,3,2-dioxastannolanes(1997-07) Ng, S.C.; Parsons, P.G.; Sim, K.Y.; Tranter, C.J.; White, R.H.; Young, D.J.; CHEMISTRYSix dibutyl-l,3,2-dioxastannolanes, including two enantiomeric pairs, exhibited greater in vitro antitumour activity towards a variety of human tumour cell lines than cisplatin but with little discrimination, suggesting hydrolysis to a common cytotoxic intermediate. A cell line hypersensitive to mitochondrial inhibitors (CI80-13S) was not sensitive to any of the test compounds, suggesting that cell mechanisms other than, or in addition to, mitochondrial function are targeted by tin antitumour agents. A pigmented melanoma cell line (MM418c5) was resistant to the test compounds, which were found to be sequestered by melanin. This resistance was not observed with triphenyltin hydroxide. © 1997 by John Wiley & Sons, Ltd.Publication Photoelectron spectroscopy study of orbital interactions. Ethynylfurans(1997-05-08) Novak, I.; Ng, S.C.; Jin, S.; Huang, H.H.; Huang, W.; CHEMISTRYHe I and He II photoelectron spectra (UPS) of isomeric mono- and bis(ethynyl)furans were recorded. The assignment of spectra was based on empirical considerations (bandwidths, He II/He I intensity variations, comparison with spectra of related molecules) and ab initio calculations. The details of orbital interactions between the ring and ethynyl π orbitals were deduced solely on the basis of experimental data. These interactions were studied for several classes of π isoelectronic molecules.Publication Syntheses, structures and properties of copper(II) complexes with thiophene-2,5-dicarboxylic acid (H2Tda) and nitrogen-containing ligands(1999-03-12) Chen, B.-L.; Mok, K.-F.; Ng, S.-C.; Drew, M.G.B.; CHEMISTRYFive copper(II) complexes with thiophene-2,5-dicarboxylic acid (H2Tda): Cu(Tda)(H2O)·(H2O)2 (1), Cu(Tda)(im)2·(H2O) (2), Cu(Tda)(im)4 (3), [Cu(Tda)(py)2]n (4) and [Cu(Tda)(bipy)(H2O)]n·n[Cu(Tda)(bipy)(H 2O)2]·2nH2O (5) (im=imidazole, py=pyridine and bipy=2,2′-bipyridine) have been synthesised and their spectroscopic and thermal properties investigated. Three of them (3, 4 and 5) are structurally characterised and the Cu atom is in five coordinate, distorted square pyramidal environments. The thiophene-2,5-dicarboxylate molecule is monodentate in 3 in which the molecular structure is stabilised by intermolecular hydrogen bonding involving two of the four non-coordinated nitrogen atoms of the imidazole ligands and carboxylate groups from adjacent Tda2-. In 4 the thiophene-2,5-dicarboxylate ion is bridging tridentate and bonded to three copper atoms to form a chain polymer with alternating 16-membered ring bridged by two Tda2- and an 8-membered ring bridged by two carboxylates. Complex 5 comprises discrete [Cu(Tda)(bipy)(H2O)2] (5a), one dimensional zig-zag chain of [Cu(Tda)(bipy)(H2O)]n (5b) and water molecules of crystallization. The thiophene-2,5-dicarboxylate molecule is monodentate in 5a and involved in intermolecular stacking interactions with 2,2'-bipyridine rings, and bidentate in 5b to bridge [Cu(bipy)(H2O)] to form a one dimensional zig-zag chain.Publication Synthesis of cationic single-isomer cyclodextrins for the chiral separation of amino acids and anionic pharmaceuticals.(2007) Tang, W.; Ng, S.C.; CHEMISTRYWe describe a protocol for the synthesis of mono-6(A)-(1-butyl-3-imidazolium)-6(A)-deoxy-beta-cyclodextrin chloride (BIMCD), a cationic, water-soluble cyclodextrin used in the chiral separation of amino acids and anionic pharmaceuticals by capillary electrophoresis. Starting from commercially available chemicals, BIMCD is synthesized in five steps. The first step involves a nucleophilic substitution between p-toluenesulfonyl chloride and imidazole to afford 1-(p-toluenesulfonyl)imidazole (A). In the second step, a nucleophilic substitution between beta-cyclodextrin and A affords mono-6(A)-(p-toluenesulfonyl)-6(A)-deoxy-beta-cyclodextrin (B). In the third step, a nucleophilic substitution between 1-bromobutane and imidazole affords 1-butylimidazole (C). In the fourth step, a nucleophilic addition between A and C affords BIMCD tosylate. In the final step, anion exchange using an ion-exchange resin yields BIMCD as a highly water-soluble solid. Each step takes up to 2 d, including the time required for product purification. The overall protocol requires approximately 6 d.