Browsing by Author "Chou, CH"

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A side-chain dendronized nonlinear optical polyimide with large and thermally stable electrooptic activity
(2004-01-27)
Luo, JD
;
Haller, M
;
Li, HX
;
Tang, HZ
;
Jen, AKY
Effect of metal oxide precursor on sintering shrinkage, microstructure evolution and electrical properties of silver-based pastes
(2002-01-01)
Chen, SY
;
Chou, CH
;
Cheng, SY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Since the shrinkage behavior of silver-based films has been correlated with the characteristics of oxide additives used, the relative role of metal oxides and metal-organic precursors in sintering shrinkage and microstructure evolution of silver films was investigated and compared in this work. Films with an oxide powder additive exhibit two-stage shrinkage behavior in contrast to one-stage continuous shrinkage, which occurs in silver films with metal-organic precursors, added. Furthermore, metal-organic precursors are less effective than metal oxide powders in reducing shrinkage of silver-based films. That can be reasonably explained that metal-organic precursors can be effectively decorated around silver powder to inhibit the sintering densification. The Zr-based organic precursor among the metal-organic precursors exhibits optimal retardation in sintering densification of silver film, which is probably interrelated to refractory characteristics of ZrO2. The unique conductivity and grain growth of silver film with 1.0 wt% tungsten-organic precursor added was possibly due to the partial dissolution of W into Ag. (C) 2002 Kluwer Academic Publishers.
Effect of surface-hydroxylated CdS nanoparticles on the morphological transformation of polystyrene-block-poly(ethylene oxide) thin films
(2004-10-06)
Yeh, SW
;
Chang, YT
;
Chou, CH
;
Wei, KH
;
材料科學與工程學系
Polystyrene-block-poly(ethylene oxide) (SEO) block copolymer thin films, in which CdS clusters have been sequestered into the PEO domains of the SEO block copolymers, are found to induce the morphological transformation of PEO from cylinders to spheres, as shown by using atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). This transformation is caused by the presence of hydrogen-bonding interactions between surface-hydroxylated CdS and PEO, as confirmed by nuclear magnetic resonance (NMR) studies.
Enhanced electroluminescence of poly(2-methoxy-5-(2 '-ethylhexyloxy)-1, 4-phenylene vinylene) films in the presence of TiO2 nanocrystals
(2006-06-01)
Weng, CC
;
Chou, CH
;
Wei, KH
;
Huang, JY
;
材料科學與工程學系
We demonstrated that in a nanocrystalline TiO2/poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) composite, electroluminescence of this composite is enhanced via addition of TiO2 nanoneedles. The TiO2 nanoneedles enhance the partial crystallization of MEH-PPV around TiO2, which in turn causes a decrease in the hole barrier height and an increase in hole mobility. The I-V measurement was established on an indium tin oxide/MEH-PPV:TiO2/Al device to identify the electrical properties of the composites.
Enhanced luminance and thermal properties of poly(phenylenevinylene) copolymer presenting side-chain-tethered silsesquioxane units
(2005-11-01)
Chou, CH
;
Hsu, SL
;
Yeh, SW
;
Wang, HS
;
Wei, KH
We have synthesized, using the Gilch polymerization method, a new series of high-brightness, soluble copolymers (POSS-PPV-co-MEHPPV) of poly(p-phenylenevinylene) (PPV) containing side-chain-tethered polyhedral oligomeric silsesquioxane (POSS) pendent units and poly(2-methoxy-5-[2-ethylhexyloxy]-1,4-phenylenevinylene) (MEHPPV). This particular molecular architecture of POSS-PPV-co-MEHPPV copolymers possesses not only a larger quantum yield (0.85 vs 0.19) but also higher degradation and glass transition temperatures relative to those of pure MEHPPV. The maximum brightness of a double-layered-configured light-emitting diode (ITO/PEDOT/emissive polymer/Ca/Al) incorporating a copolymer of MEHPPV and 10 mol % PPV-POSS was 5 times as large as that of a similar light-emitting diode incorporating pure MEHPPV (2196 vs 473 cd/m(2)).
Preparation of poly(2,5-thienyleneethylene) and poly(2,5-furyleneethylene) by vapor phase pyrolysis of (5-methyl-2-thienyl)methyl benzoate and (5-methyl-2-furyl)methyl benzoate
(1996-08-12)
Lu, YH
;
Hsu, CS
;
Chou, CH
;
Chou, TH
;
應用化學系
The synthesis-of poly(2,5-thienyleneethylene) and poly(2,5-furyleneethylene) by vapor deposition polymerization is presented. (5-Methyl-2-thienyl)methyl benzoate and (5-methyl-2-furyl)methyl benzoate were subjected to vapor phase pyrolysis above 650 degrees C to form 2,5-dimethylene-2,5-dihydrothiophene and 2,5-dimethylene-2,5-dihydrofuran. Upon condensation, both compounds spontaneously polymerize, respectively, at a temperature higher than -25 degrees C to produce poly(2,5-thienyleneethylene) and poly(2,5-furyleneethylene). The obtained poly(2,5-thienyleneethylene) is soluble in chloroform above 60 degrees C. It is a semicrystalline polymer and displays a glass transition at around 25 degrees C and a melting transition at around 160 degrees C. The synthesized poly(2,5-furyleneethylene) is insoluble in tetrahydrofuran, chloroform, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) at room temperature and only swells in DMF and DMOS above 100 degrees C. Solid-state NMR studies show that the poly(2,5-furyleneethylene) is cross-linked. The poly(2,5-furyleneethylene) is also a semicrystalline polymer exhibiting a glass transition at around 20 degrees C and a melting transition at around 110 degrees C. Solution polymerizations of 2,5-dimethylene-2,5-dihydrothiophene and 2,5-dimethylene-2,5-dihydrofuran were also carried out, respectively, in THF to yield poly(2,5-thienyleneethylene) and poly(2,5-furyleneethylene). Finally, the relative merits for the polymerization of 2,5-dimethylene-2,5-dihydrothiophene and 2,5-dimethylene-2,5-dihydrofuran by both methods are compared.
Synthesis and characterization of an efficiently fluorescent poly(phenylenevinylene) possessing pendant dendritic phenyl groups
(2005-12-13)
Dinakaran, K
;
Hsiao, SM
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Chou, CH
;
Shu, SL
;
Wei, KH
We have synthesized a thermally stable and high molecular weight fluorescent poly(phenylenevinylene) (PPV) incorporating side-chain-tethered dendritic phenyl groups (DENPPV) through Gilch route; this DENPPV has a low abundance of tolane-bisbenzyl defects. Intramolecular energy transfer from the dendritic phenyl side group to the PPV backbone was evidenced from UV-vis and photoluminescence spectra of the DENPPV polymer and its model compound. Copolymers of DENPPV with 2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene (MEHPPV) display excellent photoluminescence both in solution and in the solid state; the highest quantum yield we observed was 82%. The electroluminescence of the copolymer MEHPPV/DENPPV (molar ratio: 25/75) was 70% higher than that of MEHPPV (0.12 lm/W vs 0.07).
Synthesis and characterization of dendronized polyfluorenes
(2002-12-17)
Chou, CH
;
Shu, CF
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應用化學系
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Department of Applied Chemistry
A series of polyfluorenes containing pendant poly(benzyl ether) dendritic wedges of different generations was synthesized via the macromonomer approach, and then they were characterized by their structures and properties. The dendritic monomers were prepared by coupling benzyl bromide functionalized dendrons with 9,9-bis(4-hydroxyphenyl)-2,7-dibromofluorene and were subsequently copolymerized with a 9,9-dioctylfluorene diboronate derivative by the Suzuki coupling reaction to give the target alternating copolymers. Photophysical studies reveal that the photoluminescent properties of the dendronized polymers are greatly affected by the size of the dendritic side chains. Polymers appended with higher generation dendrons exhibit an enhanced photoluminescence efficiency and an improved luminescent stability. This is attributed to the shielding effect induced by the bulky dendrimer side chains, which prevent self-quenching and suppress the formation of aggregates/excimers.
Synthesis and characterization of fluorescent poly [fluorene-co-phenylene-1-(di-2-pyridylamine)] copolymer and its Ru(II) complex
(2004-10-01)
Dinakaran, K
;
Chou, CH
;
Hsu, SL
;
Wei, KH
;
材料科學與工程學系
2,2'-dipyridylamine substituted poly(fluorene-co-phenylene) copolymers with different concentrations of dipyridylamine have been synthesized by Suzuki polycondensation. These polymers were found to be soluble in organic solvents such as tetrahydrofuran, chloroform, and dimethylformamide. The photoluminescence of the copolymer was slightly blueshifted as the concentration of dipridylamine was increased. The introduction of dipyridylamine and the ruthenium complex into the polymer significantly improved the photoluminescence efficiency. (C) 2004 Wiley Periodicals, Inc.
Synthesis and characterization of luminescent polyfluorenes incorporating side-chain-tethered polyhedral oligomeric silsesquioxane units
(2005-02-08)
Chou, CH
;
Hsu, SL
;
Dinakaran, K
;
Chiu, MY
;
Wei, KH
Using Suzuki polycondensation, we have synthesized polyhedral silsesquioxane-tethered polyfluorene copolymers, poly(9,9'-dioctylfluorene-co-9,9'-bis[4-(N,N-dipolysilsesquioxane)aminophenyl]fluorene) (PFO-POSS), that have well-defined architectures. This particular PFO-POSS molecular architecture increases the quantum yield of polyfluorene significantly by reducing the degree of interchain aggregation; in addition, these copolymers exhibit a purer and stronger blue light by preventing the formation of keto defects.
Synthesis and characterization of soluble poly(ether imide)s based on 2,2 '-bis(4-aminophenoxy)-9,9 '-spirobifluorene
(2003-02-01)
Reddy, DS
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Chou, CH
;
Shu, CF
;
Lee, GH
;
應用化學系
A series of aromatic poly(ether imide)s containing 9,9'-spirobifluorene moieties in the main chain have been synthesized via the polycondensation of 2,2'-bis(4-aminophenoxy)-9,9'-spirobifluorene with a variety of aromatic dianhydrides. In the diamine monomer, the two aminophenoxyfluorene entities are orthogonally arranged and are connected through an sp(3) carbon atom (the spiro center). The resulting poly(ether imide)s have a polymer backbone which is periodically twisted with an angle of 90degrees at each spiro center. This structural feature, which restricts the close packing of the polymer chains and reduces inter-chain interactions, leads to amorphous poly(ether imide)s with good solubility in common organic solvents. In addition, the rigidity of the main chain of these polymers appears to be preserved due to the spiro-structure. As a result, these poly(ether imide)s exhibit a high T-g and excellent thermal stability. (C) 2002 Elsevier Science Ltd. All rights reserved.
Synthesis and characterization of spirobifluorene-based polyimides
(2002-11-01)
Chou, CH
;
Reddy, DS
;
Shu, CF
;
應用化學系
;
Department of Applied Chemistry
The synthesis and properties of organosoluble aromatic polyimides, containing spiro-skeletal units in the polymer backbone on the basis of the spiro-diamine monomer, 2,2'-diamino-9,9'-spirobifluorene, are described. In the case of the Spiro segment, the two fluorene rings are orthogonally arranged and connected through a tetrahedral bonding carbon atom, the Spiro center. As a consequence, the polymer chain is periodically zigzagged with a 90degrees angle at each Spiro center. This structural feature minimizes interchain interactions and restricts the close packing of the polymer chains, resulting in amorphous polyimides that have good solubility in organic solvents. Compared with their fluorene-based cardo analogues, the spirobifluorene-based polyimides have an improved solubility. Furthermore, the main-chain rigidity of the polyimide appears to be preserved because of the presence of the spiro structure, which restricts the free segmental mobility. As a result, these polyimides exhibit a high glass-transition temperature (T-g's) and good thermal stability. The T-g's of these polyimides were in the range of 287-374 degreesC, and the decomposition temperatures in nitrogen for a 10% weight loss occurred at temperatures above 570 degreesC. (C) 2002 Wiley Periodicals, Inc. J Polym, Sci Part A: Polym Chem 40: 3615-3621, 2002.