The effect of orientation on thermal expansion behavior in polyimide films

The anisotropy of the thermal expansion of polyimide films was investigated . Out-of-plane or thickness direction coefficients of linear thermal expansion (CTE) were calculated from the difference between the coefficient of volumetric expansion (CVE) and the sum of the in-plane or film direction coefficients of linear thermal expansion for commercial and spin-coated PMDA//ODA and BPDA//PPD films and spin coated BTDA//ODA/MPD films. The CVEs were obtained from a pressure-volume-temperature (PVT) technique based on Bridgeman bellows. The CVE was shown to be essentially constant, independent of molecular orientation and thickness. A decrease in the in-plane CTEs therefore occurs at the expense of an increase in the out-of-plane CTE. In all cases the calculated out-of-plane CTE was higher than the measured in-plane CTE. The ratio of the out-of-plane CTE to the in-plane CTE was 1.2, 3.8, and 49.3 for the spin-coated BTDA//ODA/MPD, PMDA//ODA, and BPDA//PPD films, respectively. © 1994 John Wiley & Sons, Inc.     

Imidization and interdiffusion of poly(amic ethyl ester) precursors of PMDA/3,4′-ODA

Para-, meta-, and mixed isomeric poly(amic ethyl ester) precursors of the polyimide based on pyromellitic dianhydride (PMDA) and 3,4′-oxydianiline (3,4′-ODA) were synthesized. The intrinsic viscosity of each of the isomers was measured in an NMP solution and found to be less than corresponding isomers derived from PMDA and 4,4′-oxydianiline (4,4′-ODA) precursors with comparable molecular weight. The imidization and solvent retention were measured as a function of imidization temperatures, T_i using forward recoil spectrometry (FRES). For samples cast from a single solvent, either N-methyl pyrrolidone (NMP) or dimethyl sulfoxide (DMSO), no difference was observed in the temperature-dependent imidization behavior between the isomers. In all cases the imide fraction f increased as T_i increased, and reached a value of unity, i.e., full conversion at 400°C. At the same T_i, samples cast from DMSO showed a slightly higher f than samples cast from NMP. FRES and time of flight FRES (TOF-FRES) were used to measure the interdiffusion distance, w, of deuterium-labeled tracers into nondeuterated base layers of the polyimide of PMDA/3,4′-ODA treated at various T_i. The primary determinant of w for all isomers was T_i, and the particular isomer used as either the base or the tracer molecule did not seem to affect w. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2247–2258, 1998     

PMDA-BPDA-HAB聚苯并噁唑的合成及耐热性

PMDA-BPDA-HAB聚苯并噁唑的合成及耐热性;均苯四甲酸二酐;联苯四羧酸二酐;二羟基联苯胺;聚酰亚胺;聚苯并噁唑;耐热性     

Molecular structure of graphite-polyimide interphases

The molecular orientation of adsorbed polyimides and model compounds with respect to highly oriented pyrolytic graphite (HOPG) surfaces was determined by reflection-absorption infrared (RAIR) spectroscopy. As the thickness of the pyromellitic diimide (PMDI) films decreased, bands near 766 and 729 cm^-1, which were assigned to the CNC out-of-plane bending modes, were relatively strong in the spectra, demonstrating that PMDI was adsorbed flat-down with the imide rings parallel to the HOPG surface. As the thickness of the N,N'-diphenylpyromellitic diimide (DPPMDI) films was decreased, bands near 1785 and 1722 cm^-1 which were assigned to the C=O stretching modes, were relatively strong in the RAIR spectra. Moreover, bands near 869, 841, 742, and 686 cm^-1 attributed to the out-of-plane bending modes of monosubstituted benzene rings became considerably stronger. It was suggested that the DPPMDI molecules nearest to the HOPG surface were adsorbed edge-on with the carbonyl groups perpendicular to the surface and with the monosubstituted benzene rings parallel to the surface. There were significant differences in relative band intensity observed between the transmission and RAIR spectra of polyimides derived from pyromellitic dianhydride (PMDA) and oxydianiline (ODA). The band near 1725 cm^-1 due to the C=O stretching mode increased its relative intensity in the RAIR spectra of PMDA/ODA polyimides, while the bands near 1499 and 1237 cm^-1 due to the ODA moieties decreased their relative intensities, implying that PMDA moieties were oriented edge-on with the carbonyl groups perpendicular to the surface and that the ODA moieties were oriented mostly parallel to the surface. However, the RAIR spectra obtained from PMDA and 2,2-bis[4-(4-aminophenoxy)-phenyl]-hexafluoropropane (4-BDAF) polyimides were similar to the transmission spectra of the polyimide, indicating that PMDA/4-BDAF was randomly oriented on the HOPG surface.     

Nd-Ti-V催化剂的制备及在均酐制备上的应用

采用喷涂法制备了钕改性的钒系／瓷球五元复合氧化物催化剂，实验表明：使用该催化剂，在反应温度４６０±１０℃、空速６０００～８０００ｈ－１、均四甲苯在空气中的浓度２０±３ｇ／ｍ３时，固体粗酐的收率９５％～１００％，产品的质量好，副产物少，易于精制提纯。该催化剂具有重现性好、稳定性高、使用寿命长的特点。     

Synthesis and characterization of organosoluble aromatic copolyimids

A series of aromatic copolyimides was successfully synthesized from the commercial pyromellitic dianhydride (PMDA) with a commercial diamine p-phenyldiamine (PDA) and a diamine 4,4′-methylenebis-(2-tert-butylaniline) (MBTBA) specially designed by the authors. The copolyimides were characterized by Infra-red (IR), Nuclear Magnetic Resonance (NMR), Gel Permeation Chromatography (GPC), Ultraviolet Visual (UV-Vis), Thermogravimetic Analysis (TGA) and Dynamic Mechanical Analysis (DMA). The copolyimide was precipitated in m-cresol in the polymerization process when the molar ratio of MBTBA and PDA was lower than 6/4. The number-average molecular weight of the soluble copolyimides measured by GPC was larger than 4.0 × 10⁴, and the polydispersity index was higher than 1.5. Only one glass transition temperature of these copolyimides was detected around 360°C by DMA. The copolyimides did not show appreciable decomposition up to 500°C under N₂, and the thermal stability of the copolyimide increased a little with the introduction of PDA into the polyimide main chain. Translated from Acta Polymerica Sinica, 2006, (4): 609–614 (in Chinese)     

FT-Raman investigation of the thermal curing of PMDA/ODA polyamic acids

The effect of solvent on the curing reactions of PMDA/ODA polyamic acids has been investigated using Fourier transform (FT)-Raman spectroscopy. Films of different thicknesses were cured by: (1) doctor blading 15% solids solutions onto glass slides, (2) removing all but the bound NMP, and (3) removing all the N-methypyrrolidinone (NMP). The rate of cure and final degree of conversion of the PMDA/ODA polyamic acid to polyimide increased substantially in the presence of NMP, and this effect was attributed to the plasticizing effect of the solvent. Below a critical solvent concentration, which was estimated to be approximately 40% of the NMP concentration in the bound-solvent limit, the rate of imidization slowed down considerably. Comparison of FT-Raman data for PMDA/ODA polyamic acid: (1) in solution in NMP, (2) complexed with NMP in the solid state, and (3) in the solid state after all the NMP had been removed with water, indicated that intermolecular interactions were greatest in the latter case and weakest in solution. Spectra of PMDA/ODA in NMP solution provide strong evidence for binding of NMP to the amide carbonyl in solution. © 1993 John Wiley & Sons, Inc.     

The Energetics of Large Deformations of a Single Polyimide Molecular Chain: DFT and MO Calculations

The large‐deformation energetics of a single molecular chain of the rod‐like polyimide PMDA‐PDA was investigated using DFT, ab initio MO and semi‐empirical MO methods. The force/displacement curves were calculated from tensile testing simulations along the axis of the molecular chain, allowing a discussion of the distribution and change of local strain of the molecular chain. The deformation behavior of a single PMDA‐PDA molecular chain under finite deformations as functions of bending angle and dihedral angle between PMDA and PDA groups are compared. It is found that the semi‐empirical MO calculations provide sufficient accuracy to express the energetics of large deformations except for compressive deformation.

     

Synthesis of benzophenone tetracarboxylic dianhydride and pyromellitic dianhydride incorporated biscitraconimides and their thermal polymerization

Biscitraconimides incorporated with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) were synthesised. Their curing behavior as well as thermal stabilities were investigated. The intermediate amic acids were prepared by the reaction of 4-amino 4′-citraconamic acid diphenyl sulphone, 4-amino 4′-citraconamic acid diphenyl ether, and 12-amino 1-citraconamic acid dodecane with BTDA and PMDA, respectively. Six amic acids formed were then imidized by cyclocondensation with acetic anhydride. The imide monomers were obtained and these were cured at 225–240°C. The thermal stabilities of the polymers so formed were investigated and compared. © 1996 John Wiley & Sons, Inc.