Polyamide-borax composites were prepared from solution of polyimide and the borax using N-methyl-2-pyrrolidone as a solvent. The Polyimide-borax composites films (PI-BX) characterized by FTIR, SEM and x-ray. The borax content significantly influences thermal behavior of the polymeric films, such as glass transition and decomposition temperatures of polyimide-borax composites. The glass transition temperatures of the composites were higher than that of the original polyimide. The flammability properties of them were demonstrated by cone calorimeter and indicate that the borax composites have significantly decreased in heat release rate, and mass loss rate. The PI-BX composites appears very good the flame retardant properties. 相似文献
Mixing a bis‐hydrophilic, cationic miktoarm star polymer with a linear polyanion leads to the formation of unilamellar polymersomes, which consist of an interpolyelectrolyte complex (IPEC) wall sandwiched between poly(ethylene oxide) brushes. The experimental finding of this rare IPEC morphology is rationalized theoretically: the star architecture forces the assembly into a vesicular shape due to the high entropic penalty for stretching of the insoluble arms in non‐planar morphologies. The transmission electron microscopy of vitrified samples (cryogenic TEM) is compared with the samples at ambient conditions (in situ TEM), giving one of the first TEM reports on soft matter in its pristine environment.
Abstract The HCl and DCl salts of pheny1-4-pyridyldiazomethane were prepared and irradiated at 6 K to generate the carbenes. Their ESR spectra indicated presence of plural triplet carbenes with slightly-different zero-field splitting constants. Besides the triplet species, we found a quintet species whose signal intensity decreases with increasing temperature. The quintet spin state was concluded to be a ground state which was produced by an intermolecular ferromagnetic interaction of the triplet carbenes. The ferromagnetic interaction would be explained by the McConnell mechanism, judging from the crystal structure of the HCl salt of phenyl-4-pyridylketone. 相似文献
The shift δT of the selective reflection temperature due to an exposure to γ-rays is studied for a mixture of cholesteric substances dissolved in various organic solvents. Values of δT such as 0.2°C per krad can be obtained. The influence of the solvent nature (carbon tetrachloride, chloroform, trichloroethylene, …) is also discussed. It is shown that the shift δT is due to the presence of radiolysis products of the solvent; this effect is more specially studied in the case of carbon tetrachloride containing a radical scavenger. 相似文献
The structural and optical properties of thin films of polyimide composites with nanosilica particle content of 15?wt%, prepared via sol–gel process, were studied as a function of the gamma dose. The resultant effect of gamma irradiation on the properties of polyimide/silica nanocomposite has been investigated using X-ray diffraction and UV spectroscopy. Absorption and reflectance spectra were collected by a spectrophotometer giving UV-radiation of wavelength range 200–800?nm. The optical data obtained were analyzed and the calculated values of the optical energy gap exhibited gamma dose dependence. The direct optical energy gap for the nonirradiated polyimide/silica nanocomposite is about 2.41?eV, and increases to a value of 2.65?eV when irradiated with gamma doses up to 300?kGy. It was found that the calculated refractive index of the polyamide/silica increases with the gamma dose in the range 50–300?kGy. 相似文献
To probe the molecular packing in crystalline domains of an unsymmetrical poly(benzoxazole-imide) (BPDA-BOA) introduced alternating phenylbenzoxazole and bisphthalimide units via the two-step polymerization of 5-amino-2-(4- aminophenyl)benzoxazole (BOA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), the crystal structure of its model compound, 5-phthalimido-2-(4-phthalimidophenyl)benzoxazole (PA-BOA), was investigated using powder wide-angle X-ray diffraction (WAXD) combined with molecular modeling using a Materials Studio program. Powder WAXD pattern of the model compound can be well indexed in terms of amonoclinic unit cell with parameters of a = 12.005 Å, b = 3.837 Å, c = 23.562 Å, β = 96.711°. There are two molecules in the unit cell with the space group of P2 (3). Based on the crystal structure of the model compound powders and the WAXD analysis of poly(benzoxazole-imide) film, it can be concluded that the projection of the monomer repeat length of the poly(benzoxazole-imide) chains in the chain directionis around 19.0 Å, and the interchain side-by-side distance and face-to-face distance between the centroids of two neighboring BPDA-BOA chains are around 6.10 and 4.01 Å, respectively. The difference of molecular packing between the poly(benzoxazole-imide) chains in their crystalline domains and the model compounds in their crystals are also presented. Both the side-by-side and face-to-face π-π stacking distances between two neighboring polymer chains in the poly(benzoxazole-imide) crystalline domains are significantly larger than the corresponding values between two neighboring molecules in the model compound crystals due to a more kinked and twisted conformation. 相似文献
A series of cross-linked polyimides (PIs) were prepared via two-step solution polycondensation from 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) and 2,5-furandicarboxylic acid-based diamines, N,N′-bis(4-amino-2-(trifluoromethyl)phenyl)furan-2,5-dicarboxamide (TFFDA) and N,N′-bis(4-aminophenyl)furan-2,5-dicarboxamide (p-FDDA), followed by thermal crosslinking reaction with bismaleimide. The thermal crosslinking reaction and its mechanism were studied by FTIR spectra and model reaction analysis, which showed Diels–Alder reaction between furan group and maleimide group played a main role in the thermal treatment. The properties of cross-linked PIs were characterized using dynamic mechanical thermal analysis, thermogravimetric analyses, tensile testing, ultraviolet-visible spectra, and wide-angle X-ray diffraction. The cross-linked polyimide film showed improved solvent-resistance, thermal and mechanical properties with Tg values of 234–306oC, tensile strengths of 82–98 MPa and moduli of 2.3–3.0 GPa. 相似文献
Glassy polyimide membranes are attractive for industrial applications in sour natural gas purification. Unfortunately, the lack of fundamental understanding of relationships between polyimide chemical structures and their gas transport properties in the presence of H2S constrains the design and engineering of advanced membranes for such challenging applications. Herein, 6FDA-based polyimide membranes with engineered structures were synthesized to tune their CO2/CH4 and H2S/CH4 separation performances and plasticization properties. Under ternary mixed sour gas feeds, controlling polymer chain packing and plasticization tendency of such polyimide membranes via tuning the chemical structures were found to offer better combined H2S and CO2 removal efficiency compared to conventional polymers. Fundamental insights into structure–property relationships of 6FDA-based polyimide membranes observed in this study offer guidance for next generation membranes for sour natural gas separation. 相似文献