Polyimide Blends Research Articles

Gas transport properties of hyperbranched polyimide/hydroxy polyimide blend membranes

Gas transport properties of novel hyperbranched polyimide/hydroxy polyimide blends and their silica hybrid membranes were investigated. Gas permeability coefficients of the blend membranes showed positive deviation from a semilogarithmic additive rule. The enhanced gas permeability were resulted from the increase in free volume elements caused by the intermolecular interaction between terminal amine groups of the hyperbranched polyimide and hydroxyl groups of the hydroxy polyimide backbone. Additionally, CO2/CH4 separation ability of the blend membranes was markedly promoted by hybridization with silica. The remarkable CO2/CH4 separation behavior was considered to be due to characteristic distribution and interconnectivity of free volume elements created by the incorporation of silica. For the hyperbranched polyimide/hydroxy polyimide blend system, polymer blending and hybridization techniques synergistically provided the excellent CO2/CH4 separation ability.

Effects of the aliphatic/aromatic structure on the miscibility, thermal, optical, and rheological properties of some polyimide blends

AbstractTwo binary polyimide (PI) blends having a common monomer (diamine or dianhydride) were prepared. The first system was composed of PIs obtained from an alicyclic and flexible dianhydride, namely 5‐(2,5‐dioxotetrahydrofurfuryl)‐3‐methyl‐3‐cyclohexene‐1,2‐dicarboxylic acid anhydride (DOCDA) and two aromatic diamines: 4,4′‐oxydianiline (ODA) and p‐phenylenediamine, respectively. In the second system, ODA was combined with DOCDA and (hexafluoroisopropyldiene)diphthalic dianhydride (6FDA). Films of the resulted blends were transparent, suggesting their homogeneity. According to differential scanning calorimetry data, the existence of a single Tg intermediate to those of the pure PIs confirmed the miscibility of blends. Incorporation of aliphatic and asymmetric DOCDA moieties, hexafluoropropyldiene groups and ether linkages in the molecular structure of PIs reduced the charge transfer interactions and significantly increased transparency and optical gap energy, especially for the poly(DOCDA‐ODA)/poly(6FDA‐ODA) blend. These interactions are also reflected in viscosity dependence on shear rate, indicating that they are slightly stronger when the aromatic 6FDA component prevails. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Preparation and characterization of polyimide and polyethersulfone blend membrane for gas separation

ABSTRACTPolyimides (PI) have been studied as the basic materials for preparing gas separation membranes attributable to their high gas selectivity. This paper deals with the preparation and characterization of blended polyimide membranes with polyethersulfone (PES) to study separation of ethylene from nitrogen gas at different feed pressures. For improving performance of PI membranes, two procedures were used. First, using polymeric additives such as polyvinylidene fluoride (PVDF) and PES in low content and second, blending of PI casting solution with high amount of PES. Infrared spectroscopy and scanning electron microscopy (SEM) images were employed to characterize the membranes. Pyromellitic dianhydride‐co‐4, 4′‐oxy dianiline (PMDA/ODA) polyimide membranes was synthesized using polyamic acid (PAA) as precursor materials. The ideal selectivity of 100% (ethylene permeation only) was achieved at 1 bar using PMDA/ODA polyimide membranes containing 1 wt% PVDF. Addition of PES did not have any significant influence on ideal selectivity of the prepared membranes. PES‐(PMDA/ODA) polyamic acid blend membranes were prepared using different blending ratios of PES (25 wt%) and PAA (15 wt%). The blending ratio of casting solutions of PES/PAA solutions exhibited a main influence on the ideal selectivity. The ideal selectivity of 2.9 for ethylene was achieved at 3 bar using blend membranes with 0.5 wt% PAA solution. PES‐PMDA/ODA polyimide membranes were also prepared from blend casting solutions by thermal imidization. Immiscible blend membranes were obtained at different blending ratios of the casting solutions with high gas permeance and poor selectivity. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Small Angle Neutron Scattering (SANS) characterization of electrically conducting polyaniline nanofiber/polyimide nanocomposites

Nanocomposites of polyaniline nanofibers and polyimide were fabricated and studied using small angle neutron scattering (SANS). The immiscible nature of the conformationally dissimilar polyaniline nanofiber and polyimide host is established by a series of experiments involving neutron scattering. Based on these techniques, we conclude that the crystal structure of the polyimides is not disrupted, and that there is no mixing between the two components on a molecular level. The morphology of the conducting salt component was analyzed by SANS data and was treated by two common models: Debye–Bueche ( D–B) and inverse power law (IPL). Due to deviations in the linear curve fitting over a large scattering range, neither the D-B nor the IPL model could be used to characterize the size and shape of all PANI-0.5-CSA (polyaniline camphor sulfonic acid doped polymer)/polyimide blend systems. At 1 and 2% concentration, the D–B model suggested salt domains between 20 and 70 Å with fractal geometries implied by the IPL model. As salt concentrations increased to 5%, the structures were observed to change, but there is no simple structural model that provides a suitable basis for comparison.

Preparation and properties of sulfonated poly(phenylene arylene)/sulfonated polyimide (SPA/SPI) blend membranes for polymer electrolyte membrane fuel cell applications

A novel series of sulfonated poly(phenylene arylene)s (SPAs) were successfully synthesized from 2,5-dichloro-3′-sulfobenzophenone (DCSB) and 2,2′-bis[4-(4-chlorobenzoyl)]phenoxyl perfluoropropane (BCPPF) by Ni(0)-catalyzed coupling polymerization, and subsequently used as the start materials to prepare blend membranes with sulfonated polyimide (SPI) for polymer electrolyte membrane fuel cell (PEMFC) applications. The miscible structure of the prepared blend membranes was confirmed by scanning electron microscopy (SEM). The properties required for a PEM such as ion exchange capacity, water uptake, solution uptake and dimensional change and/or in water or methanol solutions, proton conductivity and hydrolytic stability were investigated in details. The obtained blend SPA/SPI membranes showed rather high proton conductivities in both the plane and the thickness direction of the membrane. They exhibited slightly anisotropic proton conductivity in water with σ⊥/∥ values in the range of 0.85–0.90, irrespective of the introduction of SPI (σ⊥/∥=0.73). They also showed significantly enhanced stability in water and methanol solutions compared with the corresponding SPA membranes. All the results indicated that this type of blend membranes were quite promising candidates for PEMFC applications.

Curing of a network polyimide modified with a linear component

The curing and relaxation processes in polymeric composites based on blends of network and linear polyimides applied onto a filler were studied by dielectric spectroscopy. The sensitivity of dielectric spectroscopy to processes occurring in the course of curing was examined.

Enhanced thermal conductivity over percolation threshold in polyimide blend films containing ZnO nano-pyramidal particles: advantage of vertical double percolation structure

The thermal conductivity along the out-of-plane direction in polyimide (PI) blend films containing ZnO nano-pyramidal particles (ZnO-NPs) was investigated. PI blend films composed of a sulfur- and a fluorine-containing PI were prepared viaspin-coating and thermal curing of precursor solutions containing ZnO-NPs. Microphase-separated structures with “vertical double percolation (VDP)” morphology were spontaneously formed in the films, in which two phases were separately aligned along the out-of-plane direction, and ZnO-NPs were preferentially precipitated in the fluorine-containing PI phase. The blend film exhibits 410% enhancement of thermal conductivity at 27 vol% of ZnO-NPs, whereas only 90% enhancement was observed in the monophase PI film containing homogeneously dispersed ZnO-NPs. These results indicate that the VDP structure with selective incorporation of ZnO-NPs functions as an effective thermal conductive pathway.

Pretilt Angles Transition via Mixture Liquid Crystal System

We studied the state of the dual liquid crystal (LC) alignment which displays both homeotropic and homogeneous alignment on blended polyimide (PI) layer. The research was conducted using rubbing method at different imidizing temperatures and the blended PI was made using homeotropic PI having an alkyl side chain and homogeneous PI without the side chain. The uniform LC alignments were achieved, and have thermal stability. The results of contact angles were similar to that of pretilt angles.

Continuous Pretilt Angle Controlled No-Bias-Bend Pi Cell via Blended Polyimide Liquid Crystal System

The controllable pre-tilt angle of liquid crystals was investigated using a blend of horizontal and vertical polyimide prepared using a rubbing method. Various pretilt angles ranging from 0° to 90° were achieved as a function of the vertical polyimide content. We observed uniform liquid crystal alignment on the rubbing-treated blended polyimide layer. A no-bias-bend (NBB) pi cell with an intermediate pretilt angle of 47.8° was manufactured. This cell had no initial bias voltage and a low threshold voltage, which indicates that it has low power consumption. In addition, the response time of the NBB pi cell was rapid.

Enhanced Thermal Diffusivity by Vertical Double Percolation Structures in Polyimide Blend Films Containing Silver Nanoparticles

The thermal diffusivity along the out-of-plane direction (D⟂) in polyimide (PI) blend films containing silver nanoparticles (Ag-NPs) was investigated. PI blend films composed of a sulfur- and a fluorine-containing PI were prepared via spin-coating and thermal curing of the precursor solutions dissolving silver nitrate. Micro-phase-separated structures with a “vertical double percolation (VDP)” morphology were spontaneously formed in the films, in which two phases are separately aligned along the out-of-plane direction, and Ag-NPs were preferentially precipitated in the sulfur-containing PI phase. The blend films exhibited higher D⟂ values than monophase PI films containing homogeneously dispersed Ag-NPs. These results indicate that the VDP structure functions as an effective thermal conductive pathway.

PREPARATION AND PROPERTIES OF SULFONATED POLY(ARYLENE ETHER SULFONE)/SULFONATED POLYIMIDE BLEND PROTON EXCHANGE MEMBRANES

A series of sulfonated poly(arylene ether sulfone)/sulfonated polyimide(SPAES/SPI)blend proton exchange membranes were prepared by solution casting method.The SEM results showed that no phase separation was found in the blend membranes,which indicated good miscibility between the two polymers.With the introduction of SPI,the blend membranes showed much higher stability in pure methanol than the corresponding SPAES membrane.The much lower methanol uptake of the blend membranes compared to that of Nafion 112 suggested the lower methanol permeability in the formers.The thermal stability of the blend membranes was similar with their pristine ones,and the desulfonation temperatures were above 290℃ .The blend membranes displayed much higher dimensional stability than the corresponding SPAES membrane.After aging at 130℃ for 200 h,the blend membranes maintained good mechanical properties,while the SPAES membrane was dissolved in the water.As a composite of two sulfonated polymers,the blend membranes maintained a high level of ion exchange capacity (IEC) and showed high proton conductivity.They displayed comparable proton conductivity with Nafion 112 at 80% relative humidity (RH ),and higher proton conductivity than that of Nafion 112 in water.

Aliphatic–aromatic polyimide blends for H 2 separation

In this work the synthesis of a semi aliphatic BTDA-DAH polyimide and their blends with BTDA-ODA and BTDA-DDS polyimides was carried out in order to improve the H 2 permselective properties of polyimides. The syntheses were made using the well-known two steps method and the silylation method. The prepared films were characterized by FTIR, DSC, thermal stability and fluorescence spectroscopy. Intercatenary distances (d-spacing) and gas separation properties were also investigated. PI blend membranes presented only one glass transition temperature (Tg) intermediate between those of the neat polyimides. Fluorescence spectra were a useful tool to recognize electron-donor and electron-acceptor interactions indicating intermolecular charge-transfer complex (CTC) formation which were confirmed by UV–Vis absorptions. As a result, a decrease in the intercatenary distances and a shift for both IR and fluorescence bands of polyimide blends were measured. PI blend membranes showed a permeability decrease with respect to the neat ones, while the selectivity increased according to X-ray diffraction results. To analyze the polyimide blend permselectivities, H 2/CH 4, H 2/CO 2, H 2/O 2 and H 2/N 2 systems were chosen. As a result, H 2/CH 4 separation factor of PI blends was among the highest reported by other authors using traditional membrane materials.

Thermal Stability of Liquid Crystals on Blended Polyimide Layers Treated by Ion Beam Irradiation

We demonstrated the annealing effects displayed by liquid crystal antiparallel cells made from ion beam-irradiated blended polyimide layers. The pretilt angles of the liquid crystals after annealing at 90 °C for 10 min were similar to those before annealing, which demonstrates good thermal stability for liquid crystal antiparallel cells. Contact angle increases as vertical polyimide concentration increases, a trend that corresponds closely to the variation in pretilt angle. Uniform liquid crystal alignment was observed from a photomicrograph. Strong anchoring energies allowed the liquid crystal to maintain homeostasis and withstand thermal stress.

Studies on the Blends of Polyamide66 and Thermoplastic Polyimide

The influence of the content of thermoplastic polyimide (TPI) on the structure and properties of polyamide66 (PA66)/TPI blends was studied. The results indicated that the addition of TPI showed little influence on the mechanical properties of the PA66/TPI blends, and the melting and crystallization behavior of the TPI/PA66 blends was not changed obviously. However, the addition of a small quantity of TPI significantly improved the heat resistance, and lowered the friction coefficient and the wear rate of the blends in comparison with pure PA66.

High Pretilt Angle Effects on Electro-Optical Property of Ion-Beam Irradiated Liquid Crystal Cells on a Blended Polyimide Surface

We investigated the high pretilt angle effects on electro-optical properties of ion beam (IB)-irradiated liquid crystal cells on a blended polyimide surface. High pretilt angle of liquid crystals IB-irradiated on a blended polyimide surface including such as 5% and 10% of homeotropic polymer contents can be achieved. The threshold voltages of IB-irradiated twisted nematic (TN) cells on a blended polyimide surface decrease with increasing the pretilt angle. Also, the rising time of IB-irradiated TN cells decreases with increasing the pretilt angle. However the decay time of IB-irradiated TN cells increases with increasing the pretilt angle. Consequently, the electro-optical properties of IB-irradiated TN cells depend strongly on the pretilt angle in a blended polyimide surface.

High Pretilt Angle Effects on Electro-Optical Property of Ion-Beam Irradiated Liquid Crystal Cells on a Blended Polyimide Surface

We investigated the high pretilt angle effects on electro-optical properties of ion beam (IB)-irradiated liquid crystal cells on a blended polyimide surface. High pretilt angle of liquid crystals IB-irradiated on a blended polyimide surface including such as 5% and 10% of homeotropic polymer contents can be achieved. The threshold voltages of IB-irradiated twisted nematic (TN) cells on a blended polyimide surface decrease with increasing the pretilt angle. Also, the rising time of IB-irradiated TN cells decreases with increasing the pretilt angle. However the decay time of IB-irradiated TN cells increases with increasing the pretilt angle. Consequently, the electro-optical properties of IB-irradiated TN cells depend strongly on the pretilt angle in a blended polyimide surface.

Preparation and properties of cross-linked sulfonated poly(arylene ether sulfone)/sulfonated polyimide blend membranes for fuel cell application

A series of cSPAES/SPI blend membranes were prepared as proton exchange membrane by two types of sulfonated nonfluoropolymers: cross-linked sulfonated poly(arylene ether sulfone) (cSPAES) and sulfonated polyimide (SPI). The miscible structure of the blend membranes was confirmed by scanning electron microscopy. The water uptake, solvent uptake, water stability and swelling degree in water were tested. The results showed that, comparing with the corresponding cSPAES membranes, the stability of blend membranes in water and methanol solutions was significantly improved by the introduction of SPI. The blend membranes exhibited good thermal and mechanical properties, high proton conductivities which indicated promising potential for fuel cell applications.

Polyimide blend alignment layers for control of liquid crystal pretilt angle through baking

Polyimide films were used for liquid crystal (LC) alignment layers to control LC pretilt angles over the full range (8°–90°). The pretilt angles could be controlled using polyimide films prepared from polyamic acid for vertical LC alignment and using polyimide blend films prepared from two types of polyamic acids, one for vertical LC alignment and the other for planar LC alignment, by changing the baking times ranging from 40 to 180min at 230°C. The polyimide blend film could control the pretilt angle better than the polyimide prepared from just one polymer component. The LC alignment behavior was well correlated with the wettability of the polyimide films due to the fragmentation of the long alkyl side group on the polyimide surfaces by the baking process.

Surface Effects on Photo-Alignment of Polyimide Blends Containing Cinnamoyl Moiety

Polyimide containing cinnamate moiety has a good potential ability as a photo-alignment material. However, the application of photo-alignment to manufacturing LCDs is still limited due to hard to generate of pretilt angle. In order to generate large pretilt angles, some technologies are introduced. One technology is to change the ratio of the imidization and another technique is to use homeotropic alignment material. We prepared polyimide (PI) blends with fluorinated PI to control pretilt angle. Atomic force microscopy images showed surface morphology change by addition of fluorinated PI with increasing alignment angle. Photo-reactive cinnamate moiety was introduced by interfacial reaction and photochemical reactivity was confirmed by contact angle and pretilt measurement. The pretilt angle of the LC cells was about 7.2°.

SPEEK/Polyimide Blends for Proton Conductive MembranesPresented at the 1st CARISMA Conference, Progress MEA 2008, La Grande Motte, 21st–24th September 2008.

AbstractA series of membranes, based on sulphonated poly(ether ether ketone) (SPEEK)/polyimide (PI) blends, was prepared at different casting conditions. They were characterised by SEM, FTIR, DMTA, DSC, TGA, water/methanol pervaporation and impedance spectroscopy. The membranes prepared at 130 °C from blends with 10, 20 and 30 wt.‐% of PI are homogeneous, and the methanol permeabilities decreased from 28 × 10–10 kg m s–1 m–2 (plain SPEEK) to 7.21, 2.61 and 0.55 × 10–10 kg m s–1 m–2, respectively. This corresponds to a 4‐ to 57‐fold methanol crossover reduction. With this improvement, by the introduction of PI, the power density of SPEEK‐based membranes in DMFC tests could be greatly improved.