Polyimide Blends Research Articles

Fluorine 계열의 폴리머를 함유한 복합 폴리이미드 표면에서의 네마틱 액정의 프리틸트 발생의 메카니즘

The mechanisms of pretilt angle generation for a nematic liquid crystal (NLC) with negative dielectric anisotropy on the blended polyimide (PI) surface containing trifluoromethyl moiety were studied. High LC pretilt angle on the blended polymer surface with F3 was measured and the pretilt angle increased with rubbing strength. However, the low LC pretilt angle on the blended polymer surface with F1 and F2 was measured. The high LC pretilt angle generated is attributable to trifluoromethyl moiety in backbone structure on the blended PI surface. Therefore, the high pretilt angle of NLC can be achieved by using the blended polymer surface.

Effect of spinning conditions on the structure and the gas permeation properties of high flux polyethersulfone—polyimide blend hollow fibers

In this work, the effects of major spinning parameters, such as: polymer concentration, air gap distance, bore fluid composition, and take-up velocity on the structure and the permeation properties of polyethersulfone-polyimide gas separation hollow fibers are discussed in detail. It is shown that a spinning dope starts to exhibit significant chain entanglement at a critical polymer concentration. Fibers spun from this critical concentration exhibit theoretically the thinnest skin layer and minimum surface porosity. The longer the nascent hollow fiber membrane is exposed to a humid air-gap, the higher the water content in the top layer before demixing occurs. This results in higher surface porosity and gas permeance. Better mixing between the polymer solution and the bore liquid is achieved by adjusting the composition of the bore fluid (NMP/H 20). Finally, by increasing the velocity of the take-up drum, the permeance of both CO 2 and N 2 decrease while their permselectivity remains constant. Suitable selection of the spinning conditions results in gas separation hollow fibers with thin skin layers (0.1 μm), macrovoid-free substructure, high permeation rates (CO 2: 40–60 GPU) and selectivity coefficients (a CO 2/N 2: 40). These results compete directly with the performance of commercial gas separation membranes.

Polyimide and nylon 6 blend film: Preparation, characterization and thermal behavior

AbstractA polyimide blend system has been prepared from a base polyimide of BTDAODA by adding ε‐caprolactam at the poly(amic acid) stage where ε‐caprolactam undergoes polymerization to form nylon 6 during the thermal cyclodehydration of poly(amic acid). The blend has been characterized by elemental analysis. IR, 13C CPMAS NMR, XRD and simple chemical methods. The thermal analysis study (TGA and DTA) shows that the stability of the blend systems is more in the lower temperature region (up to 300°C) in comparison to the control polyimide system. The isothermal study at 400°C in inert atmosphere shows that the blend system is equally stable but the isothermal study in air at 400°C shows that the thermooxidative stability of the blend films (except BB 4) is higher. Also, isothermal study in air at 500°C shows more than 90% weight loss for all the films within 3 h, but in an inert atmosphere, the blend films show lower weight loss compared to the control film. Although the XRD pattern of all the blend and control films shows an amorphous character, the films developed some crystallinity when treated with boiling NMP where the blend films developed higher crystallinity.

Molecular aggregate formation and microphase segregation effects on the photoelectrical and photovoltaic properties of polyimide-perylenediimide composite films

The strong increase of electrophotographic sensitivity, charge carrier photogeneration quantum yield and improved photovoltaic characteristics (sandwich cells with ITO, Al electrodes) are found for films of photoconductive soluble polyimides based on doubled triphenylamine heavily doped by the soluble perylenediimides (with content up to 50-60% wt). It is shown that the effect is due to perylenediimide aggregates of some tens nanometers size which are formed during the film casting at high solvent evaporation rate. The further increase of photoelectric and photovoltaic parameters is achieved by using the films of polymer blends of polyimides with polyetherimides (Ultem-1000 type) also doped with soluble perylenediimides. In this case the effect is due to microphase segregation in doped polymer blend films caused by the partial incompatibility of polymers, that results in the formation of microregions with n- and p-types of photoconductivity contacting with each other and possible appearance of p-n bulk microheterojunctions.

Improvement of mechanical property of polyimide blends with 60Co-irradiation

Radiation effects on polyimide blends were studied at different irradiation temperatures and with different irradiation doses. The irradiation polyimides were the blends of linear polyimide (HQDPA/ODA) and 4-phenylethynyl phthalic anhydride end-capped oligomer polyimide. The tensile strength and the elongation at break of irradiated films were determined as the function of irradiation temperature and dose. Under proper conditions crosslinking reaction occurred when the polyimide blends were irradiated at high temperature. The mechanical properties of irradiated polyimide blends were found to be different from the linear polyimide.

Hybrid Alignment Technique for Wide-Viewing Liquid Crystal Displays with Multi-Domains

We introduce a hybrid double layer for liquid crystal (LC) alignment into a multi-domain vertically aligned mode. A blend of polyimide (PI) and poly(vinyl cinnamate) (PVCi) was cast onto a preformed PI layer. After curing, PVCi was extracted by washing to yield a LC alignment layer with homogeneous micro-domains uniformly distributed over the homeotropic layer. The size of homogeneous domains was strongly influenced by the weight content of PVCi as well as the solvent of PVCi. The viewing angle of ±l30° with contrast ratio of 10:1 along the direction of 45° to a polarizer was obtained from hybrid double layer LC cells with no compensation film.

Influence of crosslinking technique on the physical and transport properties of ethynyl-terminated monomer/polyetherimide asymmetric membranes

Integrally-skinned asymmetric membranes prepared from blends of polyimides and a reactive monomer were prepared and treated with various energy sources to promote crosslinking. The extent of crosslinking was monitored through differential scanning calorimetry measurements. The influence of crosslinking on the physical and transport properties was measured. Activation procedures included irradiation (UV, γ, and electron-beam) and thermal (at temperatures above and below the glass transition temperature of the polymer). Surface treatment by irradiation resulted in modest improvements in separation selectivity with little reduction in fast gas flux. Limited conversion of the ethynyl moieties was achieved (average<20%). This resulted in negligible improvements in chemical resistance or thermal stability. Irradiation using an electron-beam appears to have lead to polymer chain scission resulting in a reduced thermal stability and glass transition temperature. Thermal treatments resulted in high or complete ethynyl conversion. Complete conversion of the ethynyl units resulted in marked improvements in the resistance to chemicals, thermal stability, and gas selectivity. Because the reaction temperature was higher than the glass transition temperature of the fully reacted blend, collapse of the membrane substructure occurred accompanied by a reduction in membrane permeance. Conversely, thermal treatment at 180°C resulted in a marked increase in the permeance of the membranes with a small reduction in selectivity.

Homeotropic and Homogeneous Hybrid Alignment Layer for Wide Viewing Angle LCDs

We introduce a homeotropic and homogeneous hybrid double layer for liquid crystal (LC) alignment into a multi-domain vertically aligned mode. A blend of polyimide (PI) and poly(vinyl cinnamate) (PVCi) was cast onto a preformed PI layer. After curing, PVCi was extracted by washing to yield a LC alignment layer with homogeneous micro-domains uniformly distributed over the homeotropic layer. The size of homogeneous domains was strongly influenced by the weight content of PVCi as well as the solvent of PVCi. The viewing angle of ±30° with contrast ratio of 10:1 along the direction of 45° to a polarizer was obtained from hybrid double layer LC cells with no compensation film.

Modification of a polyimide film by blending with nylon 6. Its characterization and thermal property evaluation

A polyimide blend system has been prepared from a base polyimide of PMDA–4,4′ oxydianiline by adding ε-caprolactam at the poly(amic acid) stage where ε-caprolactam is also undergoing polymerization during the curing cycle of the polyimide. The blend has been characterized by elemental analysis, IR, 13C CPMAS NMR, XRD and simple chemical methods. The thermal analysis study (TGA, DTA & DSC) shows that the stability of the blend system is more in comparison to the control polyimide system. The isothermal study at 400°C in inert atmosphere shows that the blend system is equally stable but the isothermal study in air at 400°C shows that the blend films are more stable up to a certain extent of time compared to that of the control film. Also isothermal study in air at 500°C shows rapid loss of weight (more than 90%) for all the films but in inert atmosphere the films show higher thermal stability. XRD pattern of the blend films shows a higher crystallinity. It has been also observed that the density of the blended film is higher than that of the control film.

Thermally Stable Light-Emitting Diodes using the Blend of Polyimide and Poly(9-Vinyl Carbazole) in Hole Transporting Layer

To obtain a thermally stable organic light-emitting device, the blend film of poly(9-vinylcar-bazole) (PVK) and polyimide (PI) having high thermal stability, low thermal expansion, and good adhesion with metal was introduced as the hole-transporting layer (HTL). Overall device structure was glass/anode/ HTL/EML/cathode.

High Performance Aromatic Polyimides for Inertial Confinement Fusion Experiment: Capsule and Membrane Applications

Inertial Confinement Fusion experiments are conducted in polymer capsule in which nuclear products are located. In order to vary mechanical properties of polyimide various polyimide blends and copolymers were synthesized and compared. Polyimide blends were obtained by mixing different poly(amic acid) solutions. Dianhydride and various diamines were directly mixed to form a prepolymer in solution. Young’s modulus and coefficient of thermal expansion were measured for the different polyimide specimens. It was shown that mechanical properties of polyimide strongly depend on the composition. The effect of poly(amid acid) preparation process (blends or copolymers) is also discussed.

Chemical durability of polyimide blend films

The chemical durability of blends based on pyromellitic dianhydride–oxydianiline (PMDA–ODA) and benzophenone tetracarboxylic dianhydride–oxydianiline (BTDA–ODA) polyimides with nylon 6 is described. The stabilities of the blend films in conc. H 2SO 4 and in 40% aqueous NaOH are equivalent to that of the control film and slightly better than commercially available Kapton™ film, but the stability of the PMDA based blend films in dilute NaOH (1.5%) is better compared to the control film. The weight gains of the films in solvents like dichloromethane, methyl ethyl ketone and water are dependent on the nature of the solvent and its interaction with the blend, but the BTDA based blend films show overall better chemical resistance.

High-performance aromatic polyimides for inertial confinement fusion experiments

Inertial confinement fusion (ICF) experiments have been conducted in a polymer capsule in which nuclear products were located. To vary the mechanical properties of polyimide, various polyimide blends and copolymers have been prepared and compared. In the first case, polyimide blends are obtained by mixing different poly(amic acid) solutions (PMDA-ODA and PMDA-PDA) in NMP. In the second case, dianhydride (PMDA) and various diamines (ODA and PDA) are directly mixed in the polymerization medium to form a copolymer in NMP solution. The Young's modulus and coefficient of thermal expansion have been measured for the various polyimide film specimens. It is shown that the mechanical properties of a polyimide strongly depend on its composition. The effect of the poly(amic acid) preparation process (blends or copolymers) on the mechanical properties is not significant, and the blending of poly(amic acid) solutions leads to a copolymer.

Azimuthal Anchoring Energy and Pretilt angle of Photo-aligned Nematic Liquid Crystals on a Polyimide and Poly(vinyl cinnamate) Blend Alignment Layer

The azimuthal anchoring energy and pretilt angle of a nematic liquid crystal (E7) which was aligned on a thin layer of polyimide (PI) and poly(vinyl cinnamate) (PVCi) blend by the irradiation of polarized UV on the surface, were studied. Within a PVCi content of 10–100 wt%, the azimuthal anchoring energy remains unchanged with the decrease of the PVCi content in the blend, which is attributed to the preferential occupation of the surface by cinnamate chromophore. The blend alignment layer revealed a significantly enhanced thermal stability of azimuthal anchoring in comparison with the pure PVCi based alignment layer on account of the stiffening of the layer by the incorporated PI, which caused low thermal relaxation of the structural anisotropy developed from PVCi in the blend. The addition of PI into PVCi was also found to be effective for improving the thermal stability of the pretilt angle.

Phase transition behaviors of polyimide blends

We investigate phase behaviors of polyimide blends such as polyethermide (PEI)/polystyrene (PS), PEI/polyamideimide (PAI), PEI/polyethyleneoxide (PEO), and PAI/PEO systems. Our sample systems exhibit lower critical solution temperature (LCST) phase behaviors. In the PEI/PS system, phase transition occurred near or above the glass transition temperature ( T g) of PS and the critical temperature of the system increased with decreasing molecular weight of PS. For PEI/PAI and PEI/PEO systems, the critical temperature of PEI/PAI system is higher than that of PEI/PEO system. Phase transition temperatures of PAI/PEO systems appeared to be near or below the melting point of PEO. Theoretically, we employed the double-lattice model with a perturbation term to account for the specific interactions between polymer chains. The proposed model describes phase behaviors of the polyimide blend systems fairly well.

Alloys of polyimides with varying degree of crosslinking through antimony salts: mechanical properties characterization

Polyimides with unique thermomechanical characteristics and film forming capabilities have emerged as choice material for diversified applications in advanced technologies. Wide ranging properties could be achieved for polyimides by incorporating them with many metal salts, complexes or organic materials. The inadvertent crosslinking was introduced due to metal salt incorporation and unique polyimide alloys are prepared by blending the crosslinked and uncrosslinked polyamic acid components followed by thermal imidization. The blend components were synthesized by the reaction of polyamic acid with varying concentrations of a crosslinker (here antimony pentachloride or APC) as high as 1.67×10−2mole/dm3 (i.e. hypothetically calculated Critical Crosslinker Concentration) up to lowest of 1.67×10−6mole/dm3. This communication delves into the synthesis and characterization of polyimide blends and alloys prepared by varying degrees of crosslinking introduced via APC–Amic Acid reactions. The polyimide alloys were prepared by thermal imidization of polyamic acid blends at different curing temperature starting from 50° to 350°C. The degree of imidization, mechanical properties and the residual solvent content for blends having varying mole fractions of crosslinked or uncrosslinked components have been studied. The resultant APC-PI blends have exhibited synergism on mechanical properties. The feasibility of preparing polyimide alloys with synergistic combinations of crosslinked and uncrosslinked polyimide components was concluded.

Physicochemical characterization of alloy of polyimide with varying degree of crosslinking through diisocyanates

Polyimide alloys are prepared by blending the crosslinked and uncrosslinked polyamic acid components and followed by thermal imidization. The blend components can be synthesized by the reaction of polyamic acid with the varying concentration of crosslinker [here methylene bis (4-phenyl isocyanate or MDI)] from 1.54 × 10−2 mol/L (i.e. hypothetically calculated critical crosslinker concentration or CCC) to 1.54 × 10−6 mol/L. This communication discusses the synthesis and characterization of polyimide (PI) blends and alloys prepared by varying degrees of crosslinking introduced via isocyanate-amic acid reaction. The polyimides were prepared by thermally imidizing the polyamic acid blends at different curing temperatures from 50°C to 350°C. The degree of imidization and residual solvent content for blends having varying mole fractions of crosslinked (or branched) and uncrosslinked components and two extreme conditions and at specified temperature-time profiles have been studied. The resultant PI-MDI blends have exhibited synergism on mechanical properties. The improvement in mechanical properties, however, was significantly higher at the lower imidization temperature (i.e. 50°C to 150°C). The feasibility of preparing polyimide alloys with synergistic combinations of crosslinked and uncrosslinked polyimide components was inferred.

Thermal properties of a thermoplastic polyimide blend

Differential scanning calorimetry and dynamic mechanical analysis of blends of a new thermoplastic polyimide (TPI) and poly(ether imide) (PEI) have confirmed the full miscibility of the system over the whole composition range. Annealing of the blends above the glass transition temperature of TPI, but below its crystallization temperature, did not produce a shift in the glass transition, while physical ageing of the annealed blends also failed to reveal any indication of phase separation. The rate of crystallization of TPI was slowed by the addition of PEI, and the temperature of the maximum crystallization rate shifted upwards. The β-relaxation behavior of the blends followed a linear trend between the response of the component polymers, while the low-temperature γ-relaxation was unchanged by blending. The time scale of physical ageing of the blends did not behave in a linear fashion, and the enthalpy loss on ageing also deviated from the average. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 543–552, 1999

Thermal properties of a thermoplastic polyimide blend

Differential scanning calorimetry and dynamic mechanical analysis of blends of a new thermoplastic polyimide (TPI) and poly(ether imide) (PEI) have confirmed the full miscibility of the system over the whole composition range. Annealing of the blends above the glass transition temperature of TPI, but below its crystallization temperature, did not produce a shift in the glass transition, while physical ageing of the annealed blends also failed to reveal any indication of phase separation. The rate of crystallization of TPI was slowed by the addition of PEI, and the temperature of the maximum crystallization rate shifted upwards. The β-relaxation behavior of the blends followed a linear trend between the response of the component polymers, while the low-temperature γ-relaxation was unchanged by blending. The time scale of physical ageing of the blends did not behave in a linear fashion, and the enthalpy loss on ageing also deviated from the average. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 543–552, 1999

Miscibility and crystallization behavior of solution-blended PEEK/PI blends

Miscibility and crystallization behavior of solution-blended poly(ether ether ketone)/polyimide (PEEK/PI) blends were investigated by using DSC, optical microscopy and SAXS methods. Two kinds of PIs, YS-30 and PEI-E, which consist of the same diamine but different dianhydrides, were used in this work. The experimental results show that blends of PEEK/YS-30 are miscible over the entire composition range, as all the blends of different compositions exhibit a single glass transition temperature. The crystallization of PEEK was hindered by YS-30 in PEEK/YS-30 blends, of which the dominant morphology is interlamellar. On the other hand, blends of PEEK/PEI-E are immiscible, and the effect of PEI-E on the crystallization behavior of PEEK is weak. The crystallinity of PEEK in the isothermally crystallized PEEK/YS-30 blend specimens decreases with the increase in PI content. But the crystallinity of PEEK in the annealed samples almost keeps unchanged and reaches its maximum value, which is more than 50%. The spherulitic texture of the blends depends on both the blend composition and the molecular structure of the PIs used. The more PI added, the more imperfect the crystalline structure of PEEK. (C) 1998 John Wiley & Sons, Inc.