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  • 1
    ISSN: 0887-624X
    Keywords: polyimides ; alicyclic diamines ; thermal stability ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polyaddition reactions of alicyclic diamines such as 1,4-diaminocyclohexane (1,4-CHDA) or 4,4′-diaminodicyclohexylmethane (DCHM) and configurational isomers of 1,4-CHDA or DCHM with tetracarboxylic aromatic anhydrides in aprotic solvents were carried out to prepare high molecular weight poly(amic acid)s. Through the thermal imidization of poly(amic acid)s, several flexible polyimide films were prepared. Because of the stiffness of the alicyclic moieties in diamines, the resulting polyimides exhibit high glass transition temperatures (220-340°C) almost similar to those for corresponding aromatic polyimides which have phenylene groups in place of cyclohexyl groups, and show good thermal stability. The partial crystallization was observed for polyimides with trans-cyclohexyl moiety during the heating in differential scanning calorimetry and ascertained by wide-angle x-ray diffraction. Thus, the inhibition of the occurrence of charge transfer in polyimides is accomplished by introducing alicyclic diamines in place of aromatic diamines without reducing their thermal stability. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 2
    ISSN: 0887-624X
    Keywords: polyimides ; alicyclic diamine ; charge transfer photocrosslinking ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photosensitive polyimides with alicyclic diamines and benzophenone moiety were prepared by reactions of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) with diamines in aprotic solvents, followed by thermal or chemical imidizations. Among them the polyimide from BTDA and bis(4-amino-3-methylcyclohexyl) methane (DMDHM) can be dissolved in several organic solvents such as dichloromethane, tetrachloroethane, and N-methyl-2-pyrrolidone (NMP). In order to compare properties of the polyimides with alicyclic diamines with those of corresponding aromatic polyimides, the UV absorption spectra and fluorescence spectra of these polyimides and their model compounds were investigated. No occurrence of charge transfer at photoexcited states was ascertained for the polyimides with alicyclic diamines. The hydrogen abstraction and crosslinking during photoirradiation have been studied to learn the influence of the elimination of charge transfer process in these photosensitive polyimides. The quantum yield of hydrogen abstraction for the model compound of alicyclic polyimides is 0.56 in THF measured with HPLC. The quantum yield for the photocrosslinking reaction of the solvent-soluble polyimide with alicyclic diamine, PI(BTDA/DMDHM), was determined to be 0.004 in air from gel permeation chromatography (GPC) measurement, which is four times higher than that for photosensitive polyimides with aromatic diamines. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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  • 3
    ISSN: 0887-624X
    Keywords: poly(amide acid) ammonium salts ; poly(amide acid)s ; water-soluble polyimide precursors ; UV-vis absorption spectra ; charge transfer ; solubility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of ammonium salts of poly(amide acid)s (PAS) were prepared from various poly(amide acid)s (PAA) with tertiary amines. The solubility of poly(amide acid) ammonium salts prepared from PAA(PMDA/ODA) in water is related to the ion concentration of tertiary amines. In order to elucidate the influence of the chemical structures of poly(amide acid)s and poly(amide acid) ammonium salts on their absorption spectra, pyromellitic dianhydride (PMDA), 3,3′,4,4 ′-biphenyltetracarboxylic dianhydride (BPDA), and 3,3′,4,4 ′-benzophenonetetracarboxylic dianhydride (BTDA) were chosen to react with p-phenylenediamine (PDA) and (4,4′-diaminodicyclohexyl)methane (DCHM) to give three kinds of aromatic PAAs and three kinds of alicyclic PAAs. The corresponding PASs were prepared by the reaction of PAAs with triethanolamine (TEA). Their ultraviolet-visible (UV-vis) absorption spectra were investigated compared to those of model compounds. A transparent film without absorption above 320 nm was obtained for PAS(PMDA/DCHM). The difference in absorption spectra of PAS(PMDA/PDA) from that of PAS(PMDA/DCHM) can be related to the existence of intra- and intermolecular charge transfer (CT) for PAS(PMDA/PDA). The absorption spectra of PASs with PDA in films are red shifted compared to those of corresponding PAAs in films, while the absorption spectra of PASs in water are blue shifted compared to those of corresponding PAAs in DMF. No differences in the absorption spectra of PAAs and PASs were found in DMF/H2O (9/1) mixed solvent. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1329-1340, 1998
    Additional Material: 8 Ill.
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  • 4
    ISSN: 0887-6266
    Keywords: thermotropic liquid crystalline polyester ; fluorescence depolarization ; groundstate dimer ; excimer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photoluminescence behavior (polarization, lifetime) related to liquid-crystal (LC) formation was examined for the thermotropic liquid-crystalline polyesters poly [(ethylene terephthalate)-co-(p-oxybenzoate)] (PET40/OBA60) (OBA content: 60 mol %) and poly [(ethylene 2,6-naphthalene dicarboxylate)-co-(p-oxybenzoate)] (PEN50/OBA50) (OBA:50 mol %). The Growth of liquid-crystalline (LC) phases of PET40/OBA60 proceeded during annealing. even at low temperature (e.g., 138°C) and were promoted by an increase in annealing temperatures Ta in the experimental temperature range 138-260°C. The concentration dependence of fluorescence spectra of PET40/OBA60 in solution suggested that the fluorescences at 325 and 395 nm can be attributed to monomer and ground-state dimer, respectively. The increase in dimer fluorescence intensity and the decrease in the fluorescence anisotropy ratio r from 0.06 to -0.14 were observed with growth of LC phases. These effects are explained by an increase in the ground-state dimer population and a slight change in the dimer configuration, respectively.PEN50/OBA50 showed monomer fluorescence at 395 nm due to naphthalenedicarboxylate segments and excimer fluorescence at 430 nm. The r value for the excimer fluorescence decreased from zero to about -0.14 with growth of the LC phase. Such an extraordinary phenomena, in comparison with the usual excimer fluorescences which occurs through energy migration, could be interpreted as the result of formation of high-concentration excimer sites induced by chain orientation in LC domains. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
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  • 5
    ISSN: 0887-6266
    Keywords: thermotropic liquid-crystalline polyester ; fluorescence ; intermolecular ground-state complex ; electronic distribution ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A thermotropic liquid-crystalline (LC) polyester, poly[(ethylene terephthalate)-co-(p-oxybenzoate)] (PET40/OBA60) (OBA content: 60 mol %), is investigated by fluorescence technique using two model compounds: dimethyl terephthalate (DMT) and methyl methoxybenzoate (MMB) and is demonstrated to form an intermolecular ground-state complex between the terephthalate and OBA moieties. The change in fluorescence of PET40/OBA60 film is studied from 25°C to 450°C. The peak wavelength change for fluorescence of the intermolecular ground-state complex from 394 to 430 nm was observed in the temperature range between Tg and the LC transition temperature (115∼ 250°C). This is attributed to the electronic distribution change between terephthalate and OBA moieties in the excited state, which play roles of acceptor and donor, respectively. The increase in the fluorescence intensity from the temperature near the annealing temperature to the temperature near the isotropic temperature (287∼370°C) is suggested to be the increase in LC configuration and the formation of a more stable excited state due to the electronic distribution change between terephthalate and OBA moieties. The lifetime of PET40/OBA60 film quenched from LC temperature (300°C) to room temperature is in agreement with that of the nonannealed one, which is due to the fact that the deactivation process of the sample quenched from LC temperature is in accord with that of the nonannealed one. © 1995 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 6
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We studied the highly constraining microenvironment in unimolecular micelles (unimers) of amphiphilic random terpolymers containing sodium sulfonate, cyclododecyl (CD) or lauryl (LA) groups, and a small amount of tetraphenylporphine (H2TPP) moiety at low temperatures by using photochemical hole burning spectroscopy. The terpolymers were embedded in poly(vinyl alcohol). Only the terpolymer with CD groups forms unimers in the polymer matrix. We also measured the homopolymers containing CD or LA groups doped with H2TPP. The burned (spectral) holes were thermally more stable in the unimer with CD clusters than in the terpolymer with LA groups and in the homopolymer with CD groups. The phonon frequency is larger in the unimer with CD clusters (15.9 cm-1) than in the homopolymer containing CD groups (12.5 cm-1). The results are attributed to the “pinning down” of the H2TPP species to constrained configurations in the CD cluster.
    Additional Material: 6 Ill.
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  • 7
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Excursion temperature dependences of spectral hole profiles in photochemical hole burning for free-base systems porphyrin/poly(alkyl methacrylate)s are investigated to see the relationship between relaxation properties and chemical structure of the polymers. The irreversible change in hole width is a characteristic of each polymer and is very similar to the relaxation behavior measured mechanically and dielectrically. Poly(methyl methacrylate) (PMMA) shows the highest thermal stability of hole profiles among the polymers presently studied with no marked appearance of local relaxation at 20-100 K. Poly(ethyl methacrylate) (PEMA) and poly(isopropyl methacrylate) (PiPMA) show an increase in hole width even at 20 K with a plateau region at 50-70 K, which is attributed to the rotation of the ethyl or isopropyl group around the C—O bond. Polymers which contain more than two serial methylene groups in the side chains (poly(propyl methacrylate), poly(butyl methacrylate), poly(isobutyl methacrylate)) show a similar relaxation behavior around 50-60 K, suggesting the onset of the rotation of the terminal ethyl or isopropyl group in the ester side chain around the C—C bond. Low-density polyethylene (LDPE) shows a similar excursion-temperature dependence probably due to the existence of branched oligomethylene side chains. The relaxation behavior is independent of the nature of chromophores, which indicates that irreversible hole broadening is controlled mainly by the local motion of the host matrices.
    Additional Material: 7 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 949-954 
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A soluble fluorine-containing polyimide derived from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′-dihydroxy-4,4′-diaminobiphenyl (DHBP) was prepared and successfully crosslinked via the reaction between hexamethylene diisocyanate (HMDI) and the hydroxyl groups on the phenylene rings, leading to the formation of a soft polyimide gel. The gelation times vary according to the amount of crosslinker. Higher concentration of the crosslinker and catalyst accelerates the gelation reaction. We found that the crosslinker, HMDI, not only reacts with hydroxyl groups on the phenylene rings but also forms an oligomeric chain through the reaction with moisture. The conversion of the crosslinker was estimated from NMR. The volume changes of the gels against solvent composition were also studied. The polyimide gels swell when the N-methyl-2-pyrrolidone (NMP) weight fraction is larger than 0.80 in the mixed solvent NMP/water at 20°C. During the swelling process less time is needed for the gels to reach the equilibrium in NMP richer solvents. This is the first report as far as we know on the synthesis of a polyimide gel and the study of its properties.
    Additional Material: 4 Ill.
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  • 9
    ISSN: 1042-7147
    Keywords: Electron beam lithography ; Photosensitive polyimide ; Solvent-soluble ; Benzophenonetetracarboxylic dianhydride (BTDA) crosslinking ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Solvent-soluble and intrinsically photosensitive polyimides were prepared, and their electron beam reaction was investigated. Negative tone patterns were formed by the electron beam irradiation of PI(BTDA/DEDPM) and PI(BEDA/DEDPM). The mechanism for the pattern formation of PI(BTDA/DEDPM) was determined from transient absorption measurements, changes in the molecular weights, and IR spectrum measurements to be crosslinking via hydrogen abstraction by the triplet excited state benzophenone moiety. For the case of PI(BEDA/DEDPM), the pattern was formed by insolubilization due to chemical change in the polymer. These reactions are found to be so inhomogeneous that insolubilization of the polymer occurs at an early stage of gelation.
    Additional Material: 11 Ill.
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  • 10
    ISSN: 0887-6266
    Keywords: photoconductivity ; charge carrier ; fluorescence ; curing effect ; molecular aggregation ; polyimides with alicyclic diamines ; intermolecular interaction ; mixed layer packing ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photoconduction mechanism of a polyimide with an alicyclic diamine, PI(PMDA/DCHM), prepared from pyromellitic dianhydride (PMDA) and 4,4′-diaminodicyclohexylmethane (DCHM) was investigated. Its UV absorption spectra, fluorescence spectra, photoconductivity, and annealing effects on the photocurrent generation were measured and compared to those of CPD, N,N′-dicyclohexylpyromellitic diimide, and PI(PMDA/DMDHM) prepared from PMDA and 3,3′-dimethyl-4,4′-diaminodicyclohexylmethane (DMDHM). Photoconductivity of PI(PMDA/DCHM) depends upon the degree of molecular packing between polymer backbones. PI(PMDA/DMDHM) has no photoconductivity, probably due to a barrier to their intermolecular packing by the existence of two methyl substituents. Photoconductivity of PI(PMDA/DCHM) would be the result of the weak intermolecular interaction formed by mixed layer packing arrangement between pyromellitic moiety of one polymer backbone and N-cyclohexyl ring of another one in the ground state. Radiation absorption of this weak intermolecular interaction immediately forms a charge-transfer complex in the excited state and produces radical cation and anion charge carriers, which lead to the photoconductivity in the bulk polyimide film of PI(PMDA/DCHM). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1433-1442, 1998
    Additional Material: 9 Ill.
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