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S J Shaw - One of the best experts on this subject based on the ideXlab platform.
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polyimide silica hybrids derived from an Isoimide oligomer precursor
Journal of Materials Chemistry, 2002Co-Authors: C Xenopoulos, L Mascia, S J ShawAbstract:Organic–inorganic hybrids of a cross-linked polyimide and silica were prepared via the sol–gel route using an acetylene-terminated oligomeric Isoimide and tetraethoxysilane (TEOS) precursors. Two coupling agents, γ-mercaptopropyltrimethoxysilane (MPTMS), and triethoxysilane were employed to compatibilise the organic and inorganic components of the precursor solution mixture. Homogeneous co-continuous phase morphologies could be produced with the use of MPTMS and their properties were evaluated by rheological and analytical techniques. Dynamic mechanical tests were carried out on unidirectional carbon fibre composites based on a polyimide–silica hybrid matrix. The results indicate that the thermooxidative stability of the hybrids at high temperatures is improved considerably over that of the base polyimide. However, the compatibilisation reactions of the coupling agent with the organic precursor, prior to the isomerisation–curing stages, causes a reduction in cross-linking density and a concomitant reduction in the glass transition temperature.
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Polyimide–silica hybrids derived from an Isoimide oligomer precursor
Journal of Materials Chemistry, 2001Co-Authors: C Xenopoulos, L Mascia, S J ShawAbstract:Organic–inorganic hybrids of a cross-linked polyimide and silica were prepared via the sol–gel route using an acetylene-terminated oligomeric Isoimide and tetraethoxysilane (TEOS) precursors. Two coupling agents, γ-mercaptopropyltrimethoxysilane (MPTMS), and triethoxysilane were employed to compatibilise the organic and inorganic components of the precursor solution mixture. Homogeneous co-continuous phase morphologies could be produced with the use of MPTMS and their properties were evaluated by rheological and analytical techniques. Dynamic mechanical tests were carried out on unidirectional carbon fibre composites based on a polyimide–silica hybrid matrix. The results indicate that the thermooxidative stability of the hybrids at high temperatures is improved considerably over that of the base polyimide. However, the compatibilisation reactions of the coupling agent with the organic precursor, prior to the isomerisation–curing stages, causes a reduction in cross-linking density and a concomitant reduction in the glass transition temperature.
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Variables analysis in the gelation of alkoxysilane solutions for the production of polyimide-silica hybrids
Materials Science and Engineering: C, 1998Co-Authors: C Xenopoulos, L Mascia, S J ShawAbstract:An investigation was carried out to study the effect of formulation variables on the gelation behaviour of alkoxysilane solutions based on tetraethoxysilane (TEOS) and that of corresponding polyimide-based hybrid solutions compatibilised by means of organofunctional trialkoxysilane coupling agents. The polyimide precursors used were from commercial sources, specifically a polyamic acid and an acetylene-terminated Isoimide oligomer. Formulation parameters, such as the nature of the solvent and the catalyst, the nature and amount of the coupling agent, and the type of organic polymer precursor were found to have a dominant role in the gelation behaviour of the alkoxysilane solutions. The volumetric fill ratio used for the sol-gel reactions in a closed system was also found to have a significant effect on the gelation rate of the solutions. In addition, it was established that the nature of the coupling agent used for the compatibilisation of hybrids affects the relationship between gel time and concentration. The order in which gelation is ranked in relation to formulation variables is reversed, however, in the presence of the polyimide precursor used in the alkoxysilane solution for the production of the corresponding hybrids.
F. J. Boerio - One of the best experts on this subject based on the ideXlab platform.
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Surface-Enhanced Raman Scattering As an In-Situ Probe of Polyimide/Silver Interphases
Journal of Adhesion, 1994Co-Authors: J. T. Young, F. J. BoerioAbstract:Abstract The molecular structure of interphases formed by chemically curing the polyamic acid of pyromellitic dianhydride (PMDA) and oxydianiline (ODA) against meta-aminothiophenol (m-ATP)-primed silver substrates was determined using surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (RAIR). It was found that m-ATP was adsorbed dissociatively onto silver substrates through the sulfur atoms. When polyamic acid was deposited onto silver substrates pretreated with m-ATP, acid groups of the polyamic acid combined with amino groups of m-ATP to form ammonium carboxylate salts near the interphase. SERS and RAIR results indicated that the structure of the interphase was significantly different from that of the bulk polymer. Chemical curing of the polyamic acids located in the interphase was suppressed because of the formation of ammonium carboxylate salts. However, the bulk of the polyamic acid films was highly cured to form polyimide. It was also found that more Isoimide gr...
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Surface-Enhanced Raman Scattering from Polyimide Model Compounds on Functionalized Metal Surfaces. Part I: Phthalic Anhydride/4-Aminophenyldisul de/Gold
Journal of Adhesion, 1994Co-Authors: J. T. Young, F. J. Boerio, K. M. JacksonAbstract:Abstract The interphase between a polyimide and a metal substrate was modeled by depositing phthalic anhydride (PA) onto a gold substrate pretreated with 4-aminophenyldisulfide (APDS) and then curing in a mixture of acetic anhydride and pyridine or triethylamine. Surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (RAIR) were used to characterize the model interphases. It was found that APDS was adsorbed dissociatively onto Au substrates through the sulfur atoms. The average tilt angle for APDS molecules adsorbed onto gold substrates was determined, using RAIR, to be approximately 46°. However, there was no preferred rotational angle of the adsorbed APDS molecules about the long molecular axes. When PA was deposited onto APDS-primed Au substrates, anhydride groups of PA reacted with amino groups of APDS to form amic acids. Curing these thin amic acid films in acetic anhydride catalyzed with pyridine produced mainly Isoimide species, while curing in the presence of trie...
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Surface-Enhanced Raman Scattering from Polyimide Model Compounds on Functionalized Metal Surfaces. Part II: Phthalic Anhydride/meta-Aminothiophenol/Silver
Journal of Adhesion, 1994Co-Authors: J. T. Young, F. J. BoerioAbstract:Abstract The interphase between a polyimide and a metal substrate was modeled by depositing phthalic anhydride (PA) onto a silver substrate pretreated with meta-aminothiophenol (m-ATP) and then curing in a mixture of acetic anhydride and pyridine or triethylamine. Surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (RAIR) were used to determine the molecular structure of the interphase. It was found that m-ATP was adsorbed dissociatively onto silver substrates through the thiol groups. The tilt angle for m-ATP molecules adsorbed on silver substrates was determined using RAIR to be approximately 39°. However, there was no preferred rotational angle of the adsorbed APDS molecules about the molecular axes. When PA was deposited onto m-ATP pretreated silver substrates, anhydride groups of PA reacted with amino groups of m-ATP to form amic acids. When PA/m-ATP/Ag samples were chemically cured in acetic anhydride and pyridine or triethylamine, Isoimide was the predominant pr...
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Characterization of the interface between pyromellitic dianhydride/oxydianiline polyimide and silver using surface-enhanced Raman scattering
Macromolecules, 1992Co-Authors: J. T. Young, W. H. Tsai, F. J. BoerioAbstract:SERS spectra of the polyimide obtained after curing the polyamic acid against rough silver substrates were more similar to SERS spectra of the polyamic acid than to normal Raman spectra of the polyimide, indicating that curing of the polymer was inhibited by interaction with the substrate. The results led to the conclusion that the pyromellitic dianhydride moieties were adsorbed onto the silver surface edge-on with the carbonyl bonds perpendicular to the surface. Some evidence for formation of Isoimide or degradation products containing C=N bonds in the interface was obtained.
Guodong Li - One of the best experts on this subject based on the ideXlab platform.
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thermosetting polyimides and composites based on highly soluble phenylethynyl terminated Isoimide oligomers
RSC Advances, 2014Co-Authors: Xiangsheng Meng, Zhen Wang, Guodong LiAbstract:Highly soluble phenylethynyl-endcapped Isoimide oligomers were synthesized using 2,3,3′,4′-biphenyltetracarboxylic dianhydride (3,4′-BPDA) and aromatic diamines as the monomers, 4-phenylethynyl phthalic anhydride (4-PEPA) as the end-capping reagent, and trifluoroacetic anhydride as the dehydrating agent; then high performance thermosetting polyimides and composites were produced from these oligomers via the thermal crosslinking reaction of the phenylethylnyl group and the material properties were fully investigated. A series of Isoimide oligomers with different molecular weights and a variety of chemical architectures were prepared by polycondensation of 3,4′-BPDA, 4-PEPA, and aromatic diamines including m-phenylenediamine (m-PDA), 2,2′-bis(trifluoromethyl)benzidine (TFMB), and 3,4′-oxydianiline (3,4′-ODA), followed by cyclization with trifluoroacetic anhydride. These Isoimide oligomers were characterized by means of gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), rheological measurements, intrinsic viscosity measurement, and solubility tests. Compared to their imide analogues, Isoimide oligomers showed much higher solubility in low boiling point solvents, and slightly lower melt viscosity, which can be attributed to their unique asymmetric architecture. These resins were formulated into thermosetting polyimides and composites by thermal crosslinking of the phenylethynyl group and conversion from Isoimide to imide at elevated temperatures. The properties of the thermosets and composites were studied using mechanical property measurements, dynamic mechanical thermal analysis (DMTA), and thermogravimetric analysis (TGA). The cured polyimides exhibited extremely high glass transition temperatures (Tg) up to 467 °C, and 5% weight loss temperatures (T5%) up to 584 °C in a nitrogen atmosphere. The polyimide/quartz fiber composites possessed excellent high temperature mechanical properties due to the high glass transition temperatures of matrix resins.
J. T. Young - One of the best experts on this subject based on the ideXlab platform.
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Surface-Enhanced Raman Scattering As an In-Situ Probe of Polyimide/Silver Interphases
Journal of Adhesion, 1994Co-Authors: J. T. Young, F. J. BoerioAbstract:Abstract The molecular structure of interphases formed by chemically curing the polyamic acid of pyromellitic dianhydride (PMDA) and oxydianiline (ODA) against meta-aminothiophenol (m-ATP)-primed silver substrates was determined using surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (RAIR). It was found that m-ATP was adsorbed dissociatively onto silver substrates through the sulfur atoms. When polyamic acid was deposited onto silver substrates pretreated with m-ATP, acid groups of the polyamic acid combined with amino groups of m-ATP to form ammonium carboxylate salts near the interphase. SERS and RAIR results indicated that the structure of the interphase was significantly different from that of the bulk polymer. Chemical curing of the polyamic acids located in the interphase was suppressed because of the formation of ammonium carboxylate salts. However, the bulk of the polyamic acid films was highly cured to form polyimide. It was also found that more Isoimide gr...
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Surface-Enhanced Raman Scattering from Polyimide Model Compounds on Functionalized Metal Surfaces. Part I: Phthalic Anhydride/4-Aminophenyldisul de/Gold
Journal of Adhesion, 1994Co-Authors: J. T. Young, F. J. Boerio, K. M. JacksonAbstract:Abstract The interphase between a polyimide and a metal substrate was modeled by depositing phthalic anhydride (PA) onto a gold substrate pretreated with 4-aminophenyldisulfide (APDS) and then curing in a mixture of acetic anhydride and pyridine or triethylamine. Surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (RAIR) were used to characterize the model interphases. It was found that APDS was adsorbed dissociatively onto Au substrates through the sulfur atoms. The average tilt angle for APDS molecules adsorbed onto gold substrates was determined, using RAIR, to be approximately 46°. However, there was no preferred rotational angle of the adsorbed APDS molecules about the long molecular axes. When PA was deposited onto APDS-primed Au substrates, anhydride groups of PA reacted with amino groups of APDS to form amic acids. Curing these thin amic acid films in acetic anhydride catalyzed with pyridine produced mainly Isoimide species, while curing in the presence of trie...
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Surface-Enhanced Raman Scattering from Polyimide Model Compounds on Functionalized Metal Surfaces. Part II: Phthalic Anhydride/meta-Aminothiophenol/Silver
Journal of Adhesion, 1994Co-Authors: J. T. Young, F. J. BoerioAbstract:Abstract The interphase between a polyimide and a metal substrate was modeled by depositing phthalic anhydride (PA) onto a silver substrate pretreated with meta-aminothiophenol (m-ATP) and then curing in a mixture of acetic anhydride and pyridine or triethylamine. Surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (RAIR) were used to determine the molecular structure of the interphase. It was found that m-ATP was adsorbed dissociatively onto silver substrates through the thiol groups. The tilt angle for m-ATP molecules adsorbed on silver substrates was determined using RAIR to be approximately 39°. However, there was no preferred rotational angle of the adsorbed APDS molecules about the molecular axes. When PA was deposited onto m-ATP pretreated silver substrates, anhydride groups of PA reacted with amino groups of m-ATP to form amic acids. When PA/m-ATP/Ag samples were chemically cured in acetic anhydride and pyridine or triethylamine, Isoimide was the predominant pr...
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Characterization of the interface between pyromellitic dianhydride/oxydianiline polyimide and silver using surface-enhanced Raman scattering
Macromolecules, 1992Co-Authors: J. T. Young, W. H. Tsai, F. J. BoerioAbstract:SERS spectra of the polyimide obtained after curing the polyamic acid against rough silver substrates were more similar to SERS spectra of the polyamic acid than to normal Raman spectra of the polyimide, indicating that curing of the polymer was inhibited by interaction with the substrate. The results led to the conclusion that the pyromellitic dianhydride moieties were adsorbed onto the silver surface edge-on with the carbonyl bonds perpendicular to the surface. Some evidence for formation of Isoimide or degradation products containing C=N bonds in the interface was obtained.
C. N. Whang - One of the best experts on this subject based on the ideXlab platform.
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Characteristics of polyimide films deposited by ionized cluster beam
Journal of Vacuum Science and Technology, 1994Co-Authors: C.e. Hong, S. C. Choi, C. N. Whang, T. E. ShimAbstract:Ionized cluster beam deposition (ICBD) technique has been employed to fabricate high‐purity crystalline polyimide (PI) film. The pyromellitic dianhydride (PMDA) and oxydianiline (ODA) were co‐deposited using dual ICB sources to form a polyamic acid film, which was subsequently thermally cured to form a PI film. Fourier transform infrared spectroscopy (FTIR), x‐ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM) studies show that the bulk and surface chemical properties and the crystalline structure are very sensitive to the ICBD conditions such as cluster ion acceleration voltage and ionization voltage. At optimum ICBD conditions, the PI films have a maximum imidization, negligible impurities (∼1% Isoimide), and a good crystalline structure probably due to the high surface migration energy, and surface cleaning effect. The weight average molecular weight as determined by quasielastic light scattering was found to be ∼45 000. These characteristics are superior to those of films...
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Characteristics of polyimide film deposited by ionized cluster beam
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1994Co-Authors: S. C. Choi, C.e. Hong, I.s. Choi, Kwangho Jeong, C. N. WhangAbstract:Abstract Ionized cluster beam deposition (ICBD) has been employed to fabricate high-purity polyimide (PI) films. Pyromellitic dianhydride and oxydianiline were deposited using dual ionized cluster beam (ICB) sources. X-ray photo-electron spectroscopy shows that the chemical properties of the surface are very sensitive to the ICBD conditions such as cluster ion acceleration voltage and ionization voltage. At optimum ICBD conditions, the PI films have maximum imidization, and negligible impurities (∼ 1% Isoimide). A metal-insulator-semiconductor device has been fabricated using PI as an insulator to investigate the interfacial properties. From C − V characteristics, the PI film deposited with ICB is found to have a fairly low interface trap density. The conduction mechanism in ion implanted PI film is described in terms of the conducting grain model. The main factor determining the conductivity in PI is found to be closely related to the deposited damage energy induced by ion irradiation.
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XPS and FTIR Study of the Thin Polyimide Films Fabricated by Ionized Cluster Beam Deposition
MRS Proceedings, 1991Co-Authors: K. H. Chae, S. C. Choi, Y. W. Vahc, C. N. Whang, Hyung-jin JungAbstract:ABSTRACTThe ionized cluster beam deposition (ICBD) technique has been employed to fabricate high-purity polyimide (PI) films. The pyromellitic dianhydride (PMDA) and oxydianiline (ODA) were deposited using dual ionized cluster beam (ICB) sources. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoemission spectroscopy (XPS) studies show that the bulk and surface chemical properties are very sensitive to the ICBD conditions such as cluster ion acceleration voltage and ionization voltage. At optimum ICBD conditions, the PI films have a maximum imidization and negligible impurities(∼;1% Isoimide) probably due to the high surface migration energy and surface cleaning effect.
