Kil-Yeong Choi

Synthesis of silver nanoplates with controlled shapes by reducing silver nitrate with poly(vinyl pyrrolidone) in N-methylpyrrolidone

This article describes a simple approach to the synthesis of Ag nanoplates with controlled shapes by reducing silver nitrate (AgNO3) with poly(vinyl pyrrolidone) (PVP) in N-methylpyrrolidone (NMP). The hydroxyl end groups of PVP have been shown to serve as a mild reductant for the kinetically controlled synthesis of Ag nanoplates. Here, we demonstrated that Ag nanoplates with tunable size and aspect ratio could be formed with high yields in a kinetically controlled synthesis using NMP as the reaction medium. NMP plays a critical role in the formation and growth of the nanoplate morphology. The reaction time and weight ratio of PVP to AgNO3 could both be adjusted to permit the shape-controlled synthesis of Ag nanoplates, that is, with control over the nanoplate size and aspect ratio. Shape control permitted tuning of the localized surface plasmon resonance (LSPR) peaks of these Ag nanoplates over the visible and near-IR regions.

Maneuvering the growth of silver nanoplates: use of halide ions to promote vertical growth

The unique shape and crystalline structure of Ag nanoplates provide an interesting model system for investigating the roles of capping agents in controlling the evolution of the nanostructure shape during growth. This article describes a simple approach to the synthesis of Ag nanoplates with well-controlled shapes in which halide ions (including Cl−, Br−, and I−) guide the well-defined kinetically controlled synthetic route. The presence of iodide ions promoted vertical growth in the nanoplate structure, resulting in small thick nanoplates. The time, during the nanoplate growth process, at which iodide ions were added could be adjusted to control the shapes of the Ag nanoplates by controlling the lateral and vertical dimensions of the nanoplates. This shape control method permitted tuning of the localized surface plasmon resonance (LSPR) peaks of the Ag nanoplates over the visible and near-IR regions of the spectrum.

Synthesis of a novel poly(aryl ether) with pendent N-phenylimide groups

A novel monomer with two N-phenylimide activating groups for the preparation of poly(aryl ether)s was investigated. A poly(aryl ether) was prepared by nucleophilic halide displacement from an aromatic dihalide monomer containing two N-phenylimide groups by sodium salts of bisphenol A. The monomers and the resulting polymer were characterized by FT-IR and 1H NMR spectroscopy, elemental analysis and differential scanning calorimetry (DSC). The prepared polymer with a molecular weight of 6 300 and a polydispersity of 1.37 determined by GPC is readily soluble in polar aprotic solvents, e. g. dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP). Despite the low molecular weight the polymer is thermally stable up to 390°C and has a glass transition temperature of 218°C which is identical to that of ULTEM® poly(ether imide).

Photoaging behavior of 3-D colloidal photonic crystals

Since most polymers are not inherently stable to light, their photochemical behavior remains a subject of constant interest. In this study, we investigated the photoaging behavior of polymeric colloidal photonic crystal films. As a consequence of photochemical reactions containing chain-scission, photoaging induced morphological changes in the film surface including changes in the size, surface roughness, shape, and packing structure of PS particles. These structural modifications came about the deterioration of optical properties (photonic bandgap) during photoaging. Based on our results and observations, a plausible correlation between the evolutions of the optical properties and the structural modifications during photoaging was established. Finally, the compositional modifications of the surface based on oxygen incorporation behavior caused by the photooxidation process are discussed based on the ATR-FTIR and XPS analyses.

Synthesis and characterization of new poly(amide imide)s by direct polycondensation of diamine containing diimide group and diacids using thionyl chloride

A diimide diamine (DIDA) monomer containing both an isopropylidene and arylether group was prepared by reducing the dinitro compound obtained from condensation of 4-nitrophthalic anhydride and 2,2-bis[4-(4-aminophenoxy)phenyl]propane. A series of novel poly(amide imide)s were prepared from DIDA and various diacids by direct polycondensation reaction using an equimolar amount of thionyl chloride in N-methyl-2-pyrrolidone (NMP) at room temperature. Inherent viscosities of these polymers were in the range of 22–70 mL g–1 (Mw = 28 500–120 500 by GPC, Mw/Mn = 1.55–1.80). Most of these polymers are soluble in aprotic polar solvents such as NMP and dimethylsulfoxide and even in less polar solvents, i.e. m-cresol and nitrobenzene. The films had tensile strengths in the range of 103–118 MPa. The glass transition temperatures were observed in the range of 190–285°C. The polymers were stable up to 395°C in nitrogen atmosphere, which revealed good thermal stability compared with a commercial poly(amide imide). Ein Diimid-Diamin-Monomeres (DIDA) mit sowohl einer Isopropyliden- als auch einer Arylether-Gruppe wurde durch Reduktion der entsprechenden Dinitroverbindung hergestellt, die durch Kondensation von 4-Nitrophthalsaureanhydrid und 2,2-Bis[4-(4-aminophenoxy)phenyl]propan erhalten worden war. Aus DIDA und verschiedenen Dicarbonsauren wurde durch direkte Polykondensation mit einer aquimolaren Menge Thionylchlorid in N-Methyl-2-pyrrolidon (NMP) bei Raumtemperatur eine Reihe neuer Polyamidimide erhalten. Die inharenten Viskositaten dieser Polymeren betragen 22–70 mL g–1 (Mw = 28 500–120 500, mittels GPC bestimmt, Mw/Mn = 1.55–1.80). Die Mehrzahl dieser Polymeren ist in aprotischen polaren Losungsmitteln wie NMP und Dimethylsulfoxid und sogar in weniger polaren Losungsmitteln wie m-Cresol und Nitrobenzol loslich. Die Zugfestigkeit von Filmen aus diesen Polymeren liegt im Bereich von 103–118 MPa. Die Glasubergangstemperaturen betragen 190–285°C. Die Polymeren sind unter Stickstoff bis 395°C thermisch stabil, im Vergleich zu einem handelsublichen Polyamidimid ein gur Wert.

Processable Rigid Polymers Containing Spiroacetal Units

Recent interest is very high in the practical application of rigid polymers as high performance materials. Some rigid polymers have already been commercialized or are in the development stage. However, one of the glaring drawbacks with rigid polymers has been the lack of processibility because of their insolubility and infusibility resulting from polymer backbone stiffness. To solve this problem, the current molecular designs for processable rigid polymers employ the use of (i) flexible linkages or spacers in rigid polymer main chains,1 , 2) (ii) non-linear molecular moieties,3,4) (iii) co 1 merization for breaking the regularity of polymer repeating units5) and (iv) the derivatization of side chains onto polymer backbone6–13) In this work, the molecular design concepts (i) and (iv) were used for improving the processability of the rigid polyspiroacetals.

Deformation behavior of polymeric colloidal photonic crystals induced by UV irradiation

AbstractThe deformation behavior of polymeric colloidal photonic crystals (CPCs) during UV irradiation was investigated. A CPC grown from a polystyrene (PS) colloidal suspension was prepared and exposed to UV light. The UV irradiation resulted in photochemical reactions that induced morphological changes in the surfaces of CPC, including deformations in the sizes, shapes, and packing structures of the PS particles. The crystal morphology evolution resulting from UV irradiation differed significantly from the photoaging behavior observed during exposure to a light source that mimicked natural sunlight. The structural deformations destroyed the optical properties (by deteriorating the photonic bandgap). The UV irradiation induced photooxidation processes that altered the composition of the polymer material surface.

Study of the Photo-Alignment using Photo-Sensitive Polyimide (PI) Containing Chalcone Moiety

Abstract Photosensitive polyimide containing chalcone moiety as a photoalignment layer in LCD is synthesized. Chalcone monomer is prepared through Williams reaction and DOCDA-DAP is polymerized via one-step imidization followed by introducing the prepared chalcone moiety. The solution and film of the photosensitive polyimide are irradiated with UV light and characterized by UV-vis. and FT-IR spectroscopies.

Synthesis and characterization of colorless polyimides for liquid crystal alignment layer

Abstract A series of soluble polyimides has been synthesized by polycondensation reaction of 5-(2,5-dioxotetrahydrofuryl)-3-methyl-cyclohexane-1,2-dicarboxylic anhydride (DOCDA) and the mixture of p-phenylenediamine(p-PDA) and the newly prepared diamine with pendant hexadecaoxy group(DA-L-16O) via one step polymerization in m-cresol at high temperature. The inherent viscosities of the resulting polymers measured in NMP were in the range of 0.27 to 1.42 dL/g, which was decreased with the increase of the content of the diamine with the pendant hexadecaoxy group. The obtained polyimides were highly soluble in common aprotic polar solvents and some of them were even soluble in common organic solvents such as tetrahydrofuran, cyclohexanone, chloroform. The glass transition temperatures of the polyimides were in the range of 186∼327°C and most of the polyimides had good transparency in the wavelength of 400∼700nm. The pretilt angle of liquid crystals (BL-002, Merck Ltd.) with polyimides having alkoxy side chain was investigated, which revealed that the increase of alkoxy side chain in polyimide resulted in higher pretilt angles.

Synthesis and characterization of poly(amide imide)s containing cyclohexylidene moieties with bulky substituents

Novel poly(amide imide)s (PAI) containing alkyl-substituted cyclohexylidene moieties were synthesized by conventional polycondensation of trimellitic anhydride chloride with novel aromatic diamines followed by chemical imidization using acetic anhydride and pyridine. The inherent viscosities of the resulting PAIs are relatively high and range from 71 to 112 mt g(-1). The prepared PAIs show excellent thermal stability and good solubility. The glass transition temperatures (T-g) measured by DSC are observed in the range of 312-342 degrees C. Furthermore, all the polymers are readily soluble in less hygroscopic organic solvents like cyclohexanone, gamma-butyrolactone as well as aprotic polar solvents.