Browsing by Author "Leu, CM"

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Dendritic poly(ether-imide)s: synthesis, characterization, and modification
(2001-03-01)
Leu, CM
;
Shu, CF
;
Teng, CF
;
Shiea, J
;
應用化學系
A convergent approach to the preparation of dendritic macromolecules with an aromatic ether-imide inner structure and modifiable benzyl ether chain ends is described. The structural component that constitutes the branching regions was derived from 1-(4-aminophenyl)-1,1-bis(4-hydroxyphenyl)ethane. The key steps in ether-imide dendron synthesis involve an aromatic nucleophilic displacement of an activated nitro group with phenoxide leading to the ether linkage and cyclocondensation of the amino group with 3-nitrophthalic anhydride, to give rise to the imide ring containing an activated nitro functionality. The dendritic wedges are then coupled to a polyfunctional core to complete the synthesis. The benzyl ether chain ends can be selectively removed by catalytic hydrogenolysis to produce a dendrimer with phenolic chain ends. Further modification of the chain ends is accomplished by etherfication of the phenolic groups. Structures of these dendritic poly(etherimide)s were confirmed by H-1 NMR,C-13 NMR and FTIR spectroscopy as well as by mass spectrometry. Properties such as the glass transition temperature and solubility of the dendrimer are greatly affected by the nature of the end groups. (C) 2000 Elsevier Science Ltd. All rights reserved.
Effect of reactivity of organics-modified montmorillonite on the thermal and mechanical properties of montmorillonite/polyimide nanocomposites
(2001-01-01)
Tyan, HL
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Leu, CM
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Montmorillonite/polyimide (3,3',4,4'-benzophenone tetracarboxylic dianhydride-4,4'-oxydianiline, BTDA-ODA) nanocomposites displaying different morphological, thermal, and mechanical characteristics were synthesized by involving mono-, di-, and trifunctional group swelling-agent-modified montmorillonite and poly(amic acid). It was found that the dispersion of silicate layers in BTDA-ODA shifted from intercalated to exfoliated structures when the number of functional groups of the swelling agent increased to three as evidenced from X-ray diffraction and transmission electron microscopy studies. The improved morphology of the nanocomposites resulted in their enhanced mechanical and thermal properties. In particular, a 70% increase in Young's modulus, a 50% increase in the maximum stress, and a 30% reduction in the coefficients of thermal expansion for the case of BTDA-ODA nanocomposites containing 5 wt % trifunctional group swelling-agent-modified montmorillonite as compared to that of pure BTDA-ODA.
Hyperbranched poly(aryl ether oxazole)s: Synthesis, characterization, and modification
(2000-11-14)
Gong, ZH
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Leu, CM
;
Wu, FI
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Shu, CF
;
應用化學系
In this paper the synthesis and characterization of a hyperbranched poly(aryl ether oxazoIe) with terminal phenolic groups are described. An ABB' monomer containing a pair of phenolic groups and an aryl fluoride which is activated toward displacement by the attached oxazole ring was prepared. The nucleophilic substitution of the fluoride with the phenolic group leads to the formation of ether linkage and subsequently the hyperbranched poly(aryl ether oxazole) P1. As determined by a combination of model compound studies and H-1 NMR integration experiments, the degree of branching of PI is approximately 50%. The polymer P1 is thermally stable and readily soluble in polar organic solvents. The terminal phenolic groups in P1 were easily functionalized, yielding hyperbranched polymers with a variety of functional chain ends. Physical properties, such as the glass transition temperature and the solubility of the hyperbranched poly(aryl ether oxazole)s, depended significantly on the nature of the chain ends.
Hyperbranched poly(ether ketone) with carboxylic acid terminal groups: Synthesis, characterization, and derivatization
(1999-01-12)
Shu, CF
;
Leu, CM
;
應用化學系
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Department of Applied Chemistry
A new procedure is described for the formation of a hyperbranched poly(ether ketone) with carboxylic acid terminal groups. This preparation was based on the one-step synthesis of an AB(2)-type monomer 5-phenoxyisophthalic acid using phosphorus pentoxide/methanesulfonic acid as the condensing agent and solvent. The electrophilic aromatic substitution reaction led to the formation of the al yl ketone linkage. With the help of model compounds, H-1 NMR studies revealed that the degree of branching of the poly(ether ketone) was about 55%. The terminated carboxylic acid groups were readily functionalized, yielding hyperbranched polymers with a variety of different functional chain ends. The nature of the chain ends was shown to dramatically affect physical properties of the hyperbranched macromolecules. The ammonium derivative was soluble in water and behaved as a unimolecular micelle.
Layered silicates/fluorinated polyimide nanocomposites for advanced dielectric materials applications
(2002-03-18)
Jiang, LY
;
Leu, CM
;
Wei, KH
;
材料科學與工程學系
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Department of Materials Science and Engineering
Structured silicates/fluorinated polyimide nanocomposites display excellent water-absorption retardation behavior. This leads to lower leakage-current densities and lower dielectric constants under higher humidity conditions than those of the pristine fluorinated polyimides. Part of the chemical structure of the lavered silicate used in this work is shown in the Figure.
Polyimide-side-chain tethered polyhedral oligomeric silsesquioxane nanocomposites for low-dielectric film applications
(2003-09-23)
Leu, CM
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Chang, YT
;
Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Low-dielectric-constant nanoporous films (dielectric constant, k = 2.4) with thermal integrity and controllable mechanical strength have been prepared by covalently tethering nanoporous polyhedral oligomeric silsesquioxane (POSS) molecules, 1-nm size, to the side chains of polyimide. The tethered POSS molecules in the amorphous polyimide retain a nanoporous crystal structure, but form an additional ordered architecture due to microphase separation. With this approach, the dielectric constant of the film can be tuned by the amount of POSS molecules introduced in the nanocomposite film; the polyimide molecules offer additional advantages of maintaining certain thermal and mechanical strengths.
Synthesis and characterization of dendritic poly(ether imide)s
(2000-04-18)
Leu, CM
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Chang, YT
;
Shu, CF
;
Teng, CF
;
Shiea, J
New dendritic poly(ether imide)s were synthesized by the convergent growth approach, using 1-(4-aminophenyl)-1,1-bis(4-hydroxyphenyl)ethane as the building block. The aromatic nucleophilic substitution of the building block with 3-nitro-N-phenylphthalimide led to the first-generation dendron with aminophenyl group at the focal point, which was subsequently reacted with 3-nitrophthalic anhydride to yield the dendritic wedge containing an activated nitro group; The resulting nitro functionality was allowed to react with the building block to give the second-generation dendron, which was then condensed with 3-nitrophthalic anhydride, followed by ring closure to re-form the phthalimide ring and restore a reactive nitro group. Through an aromatic nucleophilic substitution, the dendritic wedges with an activated nitro group were coupled to the polyfunctional core to form the dendritic macromolecules. Structures of the ether-imide dendrimers were fully characterized by use of a combination of techniques including H-1 NMR, C-13 NMR, IR, and mass spectrometry. The glass transition temperature of the dendrimers increased with molecular weight, and the variation was consistent with theoretical calculations. These dendritic poly(ether imide)s are soluble in various organic solvents and had a thermal stability comparable to linear poly(aryl ether imide)s.
Synthesis and characterization of hyperbranched aromatic poly(ether imide)s with terminal amino groups
(2003-12-01)
Chang, YT
;
Shu, CF
;
Leu, CM
;
Wei, KH
;
材料科學與工程學系
We synthesized an AB(2)-type monomer, 4-{4-[di(4-aminophenyl)methyl]-phenoxy}phthalic acid, which contained one phthalic acid group and two aminophenyl. functionalities. The direct self-polycondensation of the AB(2)-type monomer in the presence of triphenylphosphite as an activator afforded a hyperbranched poly(ether imide) with a large number of terminal amino groups. This polymer was characterized with H-1 NMR and IR spectroscopy. The degree of branching of the hyperbranched poly(ether imide) was approximately 56%, as determined by a combination of model compound studies and an analysis of H-1 NMR spectroscopy integration data. The terminal amino groups underwent functionalization readily. The solubility and thermal properties of the resulting polymers depended on the nature of the chain end groups. In addition, the hyperbranched poly(ether imide) was grafted with polyhedral oligomeric silsesquioxane (POSS). Transmission electron microscopy analysis revealed that the grafted POSS molecules aggregated to form a nanocomposite material. (C) 2003 Wiley Periodicals, Inc.
Synthesis and dielectric properties of polyimide-chain-end tethered polyhedral oligomeric silsesquioxane nanocomposites
(2003-06-03)
Leu, CM
;
Reddy, GM
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Wei, KH
;
Shu, CF
;
材料科學與工程學系
Nanoporous polyhedral oligomeric silsesquioxanes (POSS) containing amine groups (NH2-POSS) were reacted with poly(amic acid) having anhydride end groups to form porous POSS/polyimide nanocomposites. The van der Waals interaction between tethered POSS molecules is incompatible with the polar-polar interaction of imide segments, resulting in a self-assembled system of zigzag shaped cylinders or lamellas about 60 nm long and 5 nm wide, as determined by transmission electron microscopy. The incorporation of 2.5 mol % nanoporous POSS results in a reduction of the dielectric constant of the polyimide nanocomposite from 3.40 for the pure polyimide to 3.09 without any degradation in mechanical strength.
Synthesis and dielectric properties of polyimide-tethered polyhedral oligomeric silsesquioxane (POSS) nanocomposites via POSS-diamine
(2003-12-02)
Leu, CM
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Chang, YT
;
Wei, KH
;
材料科學與工程學系
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Department of Materials Science and Engineering
Polyimide-tethered polyhedral oligomeric silsesquioxane, (R7R'Si8O12) (POSS), nanocomposites with well-defined architectures are prepared by the copolymerization reaction of a new type of diamine monomer: POSS-diamine, 4,4'-oxydianiline (ODA), and pyromellitic dianhydride (PMDA). This type of polyimide-side-chain-tethered POSS nanocomposite presents self-assembly characteristics when the amount of POSS exceeds 10 mol %, as evidenced by transmission electron microscopy studies. Furthermore, POSS/polyimide nanocomposites have both lower and tunable dielectric constants, with the lowest value of 2.3, and controllable mechanical properties, as compared to that of pure polyimide.
Synthesis and properties of covalently bonded layered silicates/polyimide (BTDA-ODA) nanocomposites
(2002-07-01)
Leu, CM
;
Wu, ZW
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Wei, KH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Covalently bonded layered silicates/polyimide (BTDA-ODA) nanocomposites have been synthesized from gamma-(aminopropyl)triethoxysilane (APTS) grafted kenyaite and poly(amic acid). The existence of covalent bonds between APTS and silicates and between APTS and the dianhydride end groups of the polymer have been confirmed by solid-state C-13 and Si-29 nuclear magnetic resonance and infrared spectroscopy, respectively. The thermal, mechanical, and moistureabsorption retardation properties of these nanocomposites were found to improve substantially over those of neat BTDA-ODA. In particular, a maximum increase of 36 degreesC in the degradation temperature and a maximum reduction of 54% in moisture absorption are displayed by these nanocomposites.
Synthesis, modification, and characterization of hyperbranched poly(ether ketones)
(1999-11-01)
Shu, CF
;
Leu, CM
;
Huang, FY
;
應用化學系
;
Department of Applied Chemistry
This report presents the synthesis and chemical modification of hyperbranched poly(ether ketones). The polymer was conveniently prepared by direct polycondensation of an AB(2) monomer, 3,5-diphenoxybenzoic acid, using phosphorus pentoxide/methanesulfonic acid (PPMA) as the condensing agent and solvent. The hyperbranched poly(ether ketone) could be modified via the electrophilic aromatic substitution of the active phenoxy groups at the chain ends with a variety of carboxylic acids. The thermal properties of the hyperbranched poly(ether ketones) depend heavily on the nature of the chain end, with glass transition temperature ranging from -24 degrees C to 180 degrees C. Moreover, the length of the terminal alkyl groups significantly influences the solubility of the hyperbranched poly(ether ketones). By varying the chain ends, hyperbranched poly(ether ketones) soluble in either a polar or nonpolar solvent could be obtained. (C) 1999 Elsevier Science Ltd. All rights reserved.