1,721,382 research outputs found
High performance polyimides for applications in microelectronics and flat panel displays
No full textPolyimides (PIs) exhibit excellent thermal stability, mechanical, dielectric, and chemical resistance properties due to their heterocyclic imide rings and aromatic rings on the backbone. Due to these advantageous properties, PIs have found diverse applications in industry. Most PIs are insoluble because of the nature of the high chemical resistance. Thus, they are generally used as a soluble precursor polymer, which forms complexes with solvent molecules, and then finally converts to the corresponding polyimides via imidization reaction. This complexation with solvent has caused severe difficulty in the characterization of the precursor polymers. However, significant progress has recently been made on the detailed characterization of PI precursors and their imidization reaction. On the other hand, much research effort has been exerted to reduce the dielectric constant of PIs, as demanded in the microelectronics industry, through chemical modifications, as well as to develop high performance, light-emitting PIs and liquid crystal (LC) alignment layer PIs with both rubbing and rubbing-free processibility, which are desired in the flat-panel display industry. This article reviews this recent research progresses in characterizing PIs and their precursors and in developing low dielectric constant, light-emitting, and LC alignment layer PIs.X11125sciescopuskc
Probing the Self- Assembled Nanostructures of Functional Polymers with Synchrotron Grazing Incidence X- Ray Scattering
No full textFor advanced functional polymers such as biopolymers, biomimic polymers, brush polymers, star polymers, dendritic polymers, and block copolymers, information about their surface structures, morphologies, and atomic structures is essential for understanding their properties and investigating their potential applications. Grazing incidence X-ray scattering (GIXS) is established for the last 15 years as the most powerful, versatile, and nondestructive tool for determining these structural details when performed with the aid of an advanced third-generation synchrotron radiation source with high flux, high energy resolution, energy tunability, and small beam size. One particular merit of this technique is that GIXS data can be obtained facilely for material specimens of any size, type, or shape. However, GIXS data analysis requires an understanding of GIXS theory and of refraction and reflection effects, and for any given material specimen, the best methods for extracting the form factor and the structure factor from the data need to be established. GIXS theory is reviewed here from the perspective of practical GIXS measurements and quantitative data analysis. In addition, schemes are discussed for the detailed analysis of GIXS data for the various self-assembled nanostructures of functional homopolymers, brush, star, and dendritic polymers, and block copolymers. Moreover, enhancements to the GIXS technique are discussed that can significantly improve its structure analysis by using the new synchrotron radiation sources such as third-generation X-ray sources with picosecond pulses and partial coherence and fourth-generation X-ray laser sources with femtosecond pulses and full coherence.X112827sciescopu
A new class of photoreactive polymers for liquid-crystal displays: Synthesis and properties
No full textHigh performance photoreactive polyimides with various side chains were newly synthesized. These polymes contained phenylvinylpyridine moieties as phtoreactive side chains. The polymers were soluble in common organic solvents, giving a good quality of thin films. For the polymers, photoreactivity and photoaligning ability were investigated. Further, the polymers in films were evaluated as an orientation layer material to control the alignment of liquid-crystals on the surface.X115sciescopu
Blue-light-emitting polymers prepared from a new monomer having a well-defined conjugation length
No full textNew light-emitting polyimides were synthesized from the conventional polycondensation of 5,5'-bis(4-aminophenyl)-2,2' -bifuryl (PFDA) with fluorinated and non-fluorinated aromatic dianhydrides, providing a good quality of thin films: 6F-PFDA PI and ODPA-PFDA PI. Their UV-VIS absorbance and photoluminescent characteristics were investigated. The polymers emit blue and blue-greenish light in a quantum yield of 7.3-14.9%, depending on the polymer backbone. (C) 2001 Elsevier Science B.V. All rights reserved.X1121sciescopu
High temperature polyimide thin films: The effect of photosensitive (DMAEM) precursor and different backbone structures on water sorption
No full textThree different polyimide films, BPDA-PDA, PMDA-ODA, and BTDA-ODA, were prepared from amic acid and photosensitive(DMAEM) precursors. The effect of backbone structures and precursors on the water sorption and the morphological structure in polyimide thin films was investigated. Gravimetric technique was employed to study the water sorption kinetics and wide angle x-ray diffraction (WAXD) technique for the morphological structure investigation of fully cured polyimide thin films. PMDA-ODA, BPDA-PDA and BTDA-ODA polyimide films prepared from amic acid precursor exhibited water diffusivities of 10.5 x 10(-10) cm(2)sec(-1), 1.4 x 10(-10) cm(2)sec(-1), and 10 x 10(-10) cm(2)sec(-1), respectively. For the linear BPDA-PDA polyimide, photosensitive(DMAEM) precursor distrupted the packing order in the microstructure. The disordered structure of polyimide thin film affected significantly the water sorption kinetics. The diffusivity of water in BPDA-PDA polyimide thin film prepared from photosensitive precursor was increased to 5.0 x 10(-10) cm(2)sec(-1). However, for the hinged PMDA-ODA and BTDA-ODA polyimide thin films prepared from photosensitive precursor no significant changes were observed in the morphological structure and water sorption kinetics.X1110sciescopu
Synthesis and properties of photoalignable aromatic polyesters containing phenylenediacrylate units in their backbones and n-alkyl moieties in their side groups
No full textA series of poly [oxy(4-n-alkyl-3,5-benzoate)oxy-1,4-phenylenediacryloyll s (PPDA-CnBZ polymers) with high molecular weights was synthesized. These polymers exhibit excellent solubility in some common organic solvents and produce good quality films using conventional spin-casting and drying processes. The polymers are thermally stable up to 357-362 degreesC in a nitrogen atmosphere; their glass transition temperatures are greater than 121 degreesC. The photoreactions and photoalignments of the polymers were investigated using ultraviolet-visible and infrared spectroscopy, and their liquid crystal (LC) alignment properties were examined. The phenylenediacrylate (PDA) chromophores in the polyesters were found to mainly undergo photocyclization upon ultraviolet light irradiation. Irradiation of the polyester films with linearly polarized ultraviolet light (LPUVL) induces preferential orientation of the polymer main chains, while the unreacted PDA chromophores are aligned along the direction perpendicular to the electric vector of the LPUVL. All the films irradiated with LPUVL were found to align LCs in a direction perpendicular to the electric vector of the LPUVL. Moreover, these LC alignments persisted even on irradiated films annealed at temperatures up to 210 degreesC, which is much higher than the glass transition temperatures of the polyesters. These LC alignment characteristics are due to the anisotropic interactions of the LC molecules with the oriented polymer chains and with the unreacted PDA chromophores. LC alignments on the polyester film surfaces have homeotropic to homogeneous characteristics, depending on the length of the n-alkyl side group, providing strong evidence that the n-alkyl side groups of the polyesters play a critical role in determining the pretilt angles of the LCs. The LC pretilt angles were also found to be influenced by the thermal annealing history of the irradiated films. In summary, the excellent properties of the PPDA-CnBZ polymers make them promising candidate materials for use as LC alignment layers in advanced LC display devices. (C) 2004 Wiley Periodicals, lnc.X1126sciescopu
Isomeric compositions in amide acids and poly(amic acid)s derived from 1-(trifluouomethyl)-2,3,5,6-benzenetetracarboxylic dianhydride
No full textTwo different poly(amic acid)s were synthesized by the polycondensations of 1-(trifluoromethyl)-2,3,5,6-benzenetetracarboxylic dianhydride (CF3DAN) with p-phenylene diamine and benzidine. In addition, an amide acid model compound was prepared from CF3DAN and aniline. Isomeric units in the poly(amic acid)s as well as the amide acid were investigated by H-1 and C-13-nuclear magnetic resonance (NMR) spectroscopies. Spectroscopic results indicate that the major isomeric component was a CF3-meta-isomeric unit centered on the aromatic carbon substituted with the trifluoromethyl group. In particular, the amide acid compound was determined to be composed of 80 mol % CFS-meta-isomer and 20 mol % H-meta-isomer. Therefore, for the poly(amic acid)s, the minor isomeric component is speculated to be a H-meta-isomeric unit rather than a para-isomeric unit. The result might result mainly from the strong electron-withdrawable and bulky trifluoromethyl substituent in the CF3DAN monomer. The strong electron withdrawability might significantly enhance the reactivities of the adjacent carbons in the monomer to the nucleophilic attack of the amino nitrogen in the aniline and diamines, and consequently overcome the role of the bulkyness, ultimately leading to the amide acid and poly(amic acid)s rich with the CF3-meta-isomeric unit. In addition, a portion of the imide form was detected in the dried AN-CF3DAM-AN amide acid. Thus, the formation of imide linkage might be involved in a small portion for the dried poly(amic acid)s. (C) 1998 John Wiley & Sons, Inc.X1113sciescopu
WATER DIFFUSION AND SORPTION IN FILMS OF HIGH-PERFORMANCE POLY(4,4'-OXYDIPHENYLENE PYROMELLITIMIDE) - EFFECTS OF HUMIDITY, IMIDIZATION HISTORY AND FILM THICKNESS
No full textPoly(4,4'-oxydiphenylene pyromellitimide) (PMDA-ODA) films of 10-109 mu m thickness were prepared from its poly(amic acid) precursor by thermal imide-ring-closure formation at various temperatures. Water sorption in the films was measured at 25 degrees C over 22-100% relative humidity using an electromicrobalance. Water diffusion in all the films was a nearly Fickian process despite the morphological heterogeneity due to the ordered and less ordered phases. Depending upon humidity, film thickness and imidization history, the diffusion coefficient and water uptake varied in the ranges of 1 x 10(-9) to 3 x 10(-9) cm(2) s(-1) and 0.4 to 4.5 wt%, respectively. Overall, both the diffusion coefficient and the water uptake increased with increasing humidity and film thickness, but decreased as the imidization temperature and time increased. The water sorption results were interpreted by consideration of morphological variations (molecular order, chain orientation and microvoids) due to film thickness and imidization history.X1160sciescopu
Poly(ethylene-co-ethyleneoxyethylene terephthalate)s: synthesis and non-isothermal crystallization behavior
No full textA series of random copolyesters of reasonably high molecular weight was synthesized with varying composition by melt copolycondensation of dimethyl terephthalate (DMT) with ethylene glycol (EG) and diethylene glycol (DEG). Composition and molecular weight of the copolyesters were determined by H-1 NMR spectroscopy and viscometry, respectively. The copolyesters containing DEG of less than or equal to 40 mol-% are crystallizable, whereas those with DEG of >40 mol-% are amorphous. For the copolyesters containing DEG of less than or equal to 13 mol-% which were crystallized isothermally, the melting behavior was investigated by means of differential scanning calorimetry (DSC). Three endotherms were found to be influenced by the crystallization temperature and composition, and the equilibrium melting temperatures were determined. In addition, the non-isothermal crystallization behavior was investigated by DSC and analyzed by both Ozawa and modified-Avrami approaches. Regardless of the composition, the value of the Ozawa exponent ranges from 2.4 to 2.6, depending on the temperature, whereas the value of the Avrami exponent ranges from 2.5 to 3.2, depending on cooling rate. These results indicate that the nucleation and growth mechanisms of the copolyesters are independent of their composition. However, the crystallization rate is decreased by incorporating DEG units into the polymer backbone and also by lowering the cooling rate. Furthermore, incorporating DEG units into the polymer backbone increases the crystallization activation energy.X1142sciescopu
Synthesis and characterization of poly(propylene sulfite) from sulfur dioxide and propylene oxide using zinc derivatives as catalysts
No full textThe zinc glutarate catalyzed copolymerization of sulfur dioxide (SO2) and propylene oxide (PO) was investigated in detail by varying temperature, time, monomer feed ratio, and PO feed per catalyst as well as by using solvents, such as PO and chloroform. An optimized copolymerization [PO]/[catalyst] = 300, and no solvent at 60 degrees C, 40 h. [PO]/[SO2] = 1, resulted in poly(propylene sulfite) (PSS) with high molecular weight (M) over bar(n) = 42000 ((M) over bar(w)/(M) over bar(n) = 2.1) never achieved before. PPS was obtained in a yield of 66.9 g per g of catalyst (namely, 12.93 kg per mol of catalyst) and determined to consist of 90.4 mol-% sulfite-linkage and 9.6 mol-% ether-linkage. A polymer amount of ether-linkages was additionally formed as a minor component. However, no formation of cyclic propylene sulfite as byproduct was detected. In addition, zinc hexacyanoferrate(III) was prepared and used in the copolymerization as a catalyst, but showed almost no catalytic activity.X1113sciescopu
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