Polyamic Acid Solution Research Articles

Non-enzymatic polyamic acid sensors for hydrogen peroxide detection

Different polyamic acid (PAA) modified sensors for hydrogen peroxide (H2O2) detection were prepared and characterized. Electro-deposition of a chemically synthesized PAA solution was used for modification of glassy-carbon electrode, while drop-casting was used for carbon (CSPE), gold (Au-SPE) and gold nanoparticles (AuNPs-SPE) screen-printed electrodes modification. All the studies performed, including the cyclic voltammetry, electrochemical impedance spectroscopy, amperometry revealed the best analytical performances of the PAA/Au-SPE electrode with a specific sensitivity of 899μAmM−1cm−2 and a detection limit of 2μM hydrogen peroxide. The PAA/Au-SPE sensor exhibited a good selectivity for the determination of H2O2 in synthetic urine samples, and could be used to control the oxidative stress of the body.

High thermal resistance polyimide separators prepared via soluble precusor and non-solvent induced phase separation process for lithium ion batteries

Lithium ion battery separators with excellent thermal stability are highly desired to meet the requirements of electric vehicles. Basing on the excellent natures of PMDA-ODA polymide (PI) and processibility of the corresponding precursor solution of polyamic acid (PAA), the porous PI separators were prepared from the PAA precursor via non-solvent induced phase separation (NIPS) and thermal imidization process. By controlling the NIPS process, the ideal PI separator with high porosity and pore-connectivity was successfully obtained and employed in lithium ion batteries (LIBs). Besides the quite high thermal stability, this PI separator behaved excellent wettability in the liquid electrolyte and high liquid electrolyte uptake. By activated with liquid electrolyte, the ionic conductivity of the PI separator could reach as high as 2.15mS·cm−1. Compared with the cells with the typical PP separators, the cells assembled with the PI separators performed the lower resistance, the higher discharge capacity and the better rate capability. These results suggested that the PAA-NIPS process could be an efficient and applicable route for preparing high performance PI separators.

Formation mechanisms and morphological effects on multi-properties of carbon nanotube fibers and their polyimide aerogel-coated composites

Abstract This paper aims to understand the formation mechanisms and morphological effects of polymer-aerogel reinforcements that guide the production of lightweight and multifunctional carbon nanotube (CNT) fibers. The CNT fibers and the polyimide aerogel-coated CNT fiber (PIA) composites were successfully developed. CNT thin films were fabricated from an aerogel technique; these films were then mechanically rolled to form CNT fibers of various diameters and densities. The CNT fibers thus prepared were dip-coated in the polyamic acid solutions to form gel-coated fibers, which were then dried with supercritical CO2 to obtain CNT/PIA composite fibers. The composite fibers presented as a core–shell structure in which the CNT fibers were tightly wrapped by porous polyimide aerogels. The relationships between the electrical and mechanical structural properties of the composites were investigated. By controlling the diameter of CNT fibers to 500 μm, we achieved electrical conductivity of 418 S/cm, and strength and stiffness values of 11.6 and 68.1 MPa, respectively.

Simulation of polyimide fibers with trilobal cross section produced by dry-spinning technology

As one type of high performance fibers, polyimide fibers can be prepared from polyamic acid (PAA) solution by dry-spinning technology. The transformation from the precursor of polyamic acid to polyimides via thermal cyclization reaction in the dry-spinning process is a main distinguishing feature, which is very different from other fibers produced by dry-spinning such as cellulose acetate fiber and polyurethane fiber. In this report, the dry-spinning formation of polyimide fibers with trilobal cross section from PAA solution in N,N-dimethylacetamide is simulated via a one-dimensional model based on a viscoelastic constitutive equation, combined with profile degree equation of cross section and imidization kinetics equation. The glass transition temperature, imidization degree and profile degree of the filament along the spinline are predicted by the model, as well as relative parameters such as solvent mass fraction and temperature. As a simulated result, solidification of polyimide fibers take place about 150 cm from the spinneret which is farther than for cellulose acetate fiber (70 cm). Moreover, the final profile degree of fiber is affected by many spinning parameters, such as spinning temperature, surface tension, spinning solution concentration, major, and minor axis length of the spinneret hole. POLYM. ENG. SCI., 55:2148–2155, 2015. © 2015 Society of Plastics Engineers

Thermal, mechanical and thermomechanical properties of tough electrospun poly(imide-co-benzoxazole) nanofiber belts

Electrospun PI-co-PBO nanofiber belts possessed superior thermomechanical properties.

Synthesis of Cu or Cu2O-polyimide nanocomposites using Cu powders and their optical properties

Nanocomposites consisting of Cu or Cu2O nanoparticles in various polyimide (PI) films were successfully prepared using polyamic acid (PAA) and Cu powders. Cu powders were dissolved into PAA solutions, and the solutions were spin-coated onto the substrates. Cu or Cu2O nanoparticles were formed in PI film by curing in a reducing or inert atmosphere, respectively. The Cu nanoparticles were transformed to Cu2O nanoparticles by post-heat treatment in an oxidizing atmosphere after curing in a reducing atmosphere. Transmission electron microscopy showed that uniform, round Cu2O nanoparticles 6.0 nm in diameter were dispersed in the PI film by post-heat treatment. The addition of Cu2O nanoparticles in the 4,4′-(hexafluoroisopropylidene)diphthalic anhydride-4,4′-oxydianiline (6FDA-ODA) PI film enhanced the refractive index of the 6FDA-ODA PI film from 1.60 to 1.72 at 633 nm, and the transparency of the nanocomposite film was about 70–90% in the visible region and remained around 90% beyond 550 nm.

Rheological behaviour of polyamic acid spinning solutions containing heterocycle

The rheological behaviour of polyamic acid (PAA) solution was studied using N,N-dimethylacetamide (DMAc) as a solvent. The results showed that the PAA/DMAc solution with solid contents of 11–15 wt-% was a shear-thinning fluid. The non-Newtonian behaviour of the solution increased with increasing PAA concentration and decreasing temperature. The complex viscosity (η*) increases upon the concentration of PAA solution. Storage modulus and loss modulus increase with increasing frequency and an obvious plateau modulus appears, exhibiting a typical solid-like behaviour at high frequencies. The PAA solution with higher solid content shows lower tangent loss angle (tan δ), higher storage modulus and loss modulus. Increasing temperature plays an opposite role in increasing polymer concentration on complex viscosity, storage modulus, loss modulus and tan δ.

Influence of hydrogen‐bonding interaction introduced by filled oligomer on bulk properties of blended polyimide films

ABSTRACTSpecific structure oligomer is designed and synthesized to fill “blank interaction points” left among polyimide (PI) rigid‐rod structure in order to further enhance the interaction between PI macromolecules. An oligomer, 4,4′‐bisbenzamide diphenyl ether (BADE) containing amide groups as proton donor, was blended with polyamic acid (PAA) solution to modify PI of pyromellitic dianhydride and 4,4′‐oxydianiline. Fourier transform infrared and dynamic mechanical analyses show that hydrogen‐bonding interaction occurs between NH groups and PI chains. This resulted interchain interaction increases the tensile strength of blended PI films from 115.9 to 135.6 MPa, about 17.0% improvement, with BADE content surprisingly up to 20 wt %. BADE is uniformly dispersed without aggregation within a saturated amount of 20 wt % through wide angle X‐ray diffraction and morphology characterization. Moreover, rheological measurements indicate that the processability of PAA solution is maintained after introduction of BADE. The obtained PI films still have excellent thermal stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40498.

Hydroscopicity and Dielectric Properties of Polyimide Containing Biphenyl and Bis-Benzimidazole Rings

A kind of Polyimide films (PI films) containing biphenyl and bis-benzimidazole rings were prepared from the its precursor Polyamic acid (PAA) solution synthesized by aromatic diamine containing biphenyl and bis-benzimidazole rings with different commercial aromatic dianhydrides. The PI films exhibited excellent hydrophobicity with the contact angle of higher than 90o and the hydroscopicity are lower than 1%. The PI films also have great dielectric properties of the dielectric constant ranges from 2.10 to 2.94 under the voltage frequency within 1 to 106HZ.

Thermal Imidization Process of Electrospun Poly(amic acid) Film Studied by In-situ FTIR

Polyamic acid(PAA) solution based on 4,4'-diaminodiphenyl ether(ODA) and pyromelliticdianhydride( PMDA) was prepared and electrospun into PAA nanofiber films. In-situ Fourier transform infrared(FTIR) spectroscopy was used to study the progress of imidization. Through applying the optimized condition of imidization,a polyimide film was obtained with 100% of imidization degree. The results show that lower heating rate(2 ℃ /min) leads to a 100% of imidization degree; PAA nanofiber films exhibited lower imidization degree under the faster rate. A new fast-slow heating rate method can improve the imidization efficiency.

Large-scale fabrication of polyimide fibers containing functionalized multiwalled carbon nanotubes via wet spinning

Functionalized multiwalled carbon nanotubes (f-MWNTs)/polyamic acid (PAA) solution was prepared via in situ polymerization. Transmission electron microscopy conformed the homogeneous dispersion of f-MWNTs in the polymer matrix. The diffusion rate of N,N-dimethylacetamide in f-MWNT/PAA solution into water shows a significant acceleration upon f-MWNT loadings. PAA composite fibers containing various loadings of f-MWNTs were produced by traditional wet-spinning process, and then the precursor fibers were converted to corresponding polyimide fibers via thermal imidization. Scanning electron microscopy, atomic force microscopy and X-ray scattering were employed to characterize the composite fibers. The thermal stability of polyimide fibers shows an obvious improvement with the incorporation of f-MWNTs. Meanwhile, f-MWNTs hinder the motivation of macromolecular chains, resulting in a reduced heat-shrinkage of the composite fibers. Exceptional enhanced mechanical properties of composite fibers were obtained due to the introduction of f-MWNT nanofillers.

Polyimide fibers prepared by dry-spinning process: imidization degree and mechanical properties

Polyimide fibers were prepared by dry spinning a polyamic acid solution to get the precursor fibers and then the precursor fibers were transferred into the polyimide fiber by heat treatment. The imidization degree (ID) of the precursor fibers obtained at various spinning conditions was investigated using FTIR and TGA analysis. As a result, the IDs of the precursor fibers increased with elevating spinning temperature. Meanwhile, the IDs measured by FTIR and TGA were much higher than the values from our model prediction. The tensile strength of precursor fibers exhibited a slight dependency on IDs. On the other hand, the complete imidization and hot stretching led to a great improvement in the mechanical properties. Subglass transition and glass transition of the stretched polyimide fibers were observed in DMA, and the activation energy of these transitions was 346 and 981 kJ mol−1, respectively.

Microstructures of BPDA-PPD polyimide thin films with different thicknesses

The microstructures of 3,4,3′,4′-biphenyltetracarboxylic dianhydride –p-phenylene diamine (BPDA-PPD) polyimide (PI) thin films with different thicknesses were investigated by grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XRR) at the SPring-8 synchrotron radiation facility. The film density calculated from XRR profiles increased with decreasing the film thickness. Processing of PI thin films from precursor polyamic acid (PAA) solutions involves simultaneous thermal imidization, evaporation of residual solvents and crystallization. The thickness reduction during imidization was smaller for the thinner PAA film. This implies that the much more larger amount of the residual solvent in the thinner PAA film brings high molecular mobility, which results in the higher conversion to PI at any curing temperature. The thinner BPDA-PPD film was more dense than the thicker film because of better molecular packing, which is a result of much more amount of the residual solvent for the thinner film during the thermal curing.

Fabrication and Properties of Flexible OLEDs on Polyimide-Graphene Composite Film Substrate

In this work a clear polyimide (PI) film was synthesized by using selected monomers containing multiple CF3 groups. The polyimide-graphene composite films were made by film coating of mixture of polyamic acid (precursor of polyimide) solution with reduced grapheme oxide. The flexible OLEDs were fabricated by using the polyimide-graphene composite films on which the ITO/Ag/ITO thin films were deposited by roll-to-roll sputter instead of usual ITO-glass and the properties of flexible OLEDs were examined from the viewpoint of flexible substrates.

Retraction notice to “Electrical conduction of polyimide films prepared from polyamic acid (PAA) and pre-imidized polyimide (PI) solution”

Electrical conduction characteristics in two different polyimide films prepared by the imidization of polyamic acid (PAA) and pre-imidized polyimide (PI) solution were investigated. It is found that the current density of the polyimide film from PAA was higher than that of the polyimide film from PI at the same electric field, even though the conduction mechanism in both polyimide films follows the ionic hopping model. The hopping distance was calculated to be 2.8 nm for PAA type and 3.2 nm for PI type polyimide film. It is also found that the decay rate of the residual electrostatic charges on the polyimide films becomes faster in the PAA type than in the PI type polyimide film.

Surface properties of aromatic polymer film during thermal treatment

Aromatic polyimide films are processed from polyamic acid solutions. This process involved the simultaneous loss of solvent and chemical conversion of polyamic acid to polyimide, and implied structural reorganization which led to changed physical properties. Polymer films generated from benzophenonetetracarboxylic dianhydride and 4,4′-diamino-3,3′-dimethyl diphenylmethane have been investigated at different stages of thermal treatment. The surface polarity, which was determined by the presence of polar COOH and CONH groups, changed during polyamic acid thermal treatment. These polar groups were removed step by step by imidization process leading to the modification of the physical properties of the polymer film.

Fabrication and Thermal Properties of Polyimide/Ba0.77Sr0.23TiO3 Nanocomposites

Polyimides (PIs) are considered to be one of the most important engineering materials. The nano-particle of barium strontium titanate (BST) with formulation of Ba0.77Sr0.23TiO3 was synthesized by the sol-gel method. In this process, different contents of BST suspensions in polyamic acid (PAA) solution were imidized by heat treatment to form PI/BST nanocomposites. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), simultaneous thermal analysis (STA), scanning electron microscope (SEM), and transmission electron microscopy (TEM) were used to characterize the structure and properties of the obtained nanocomposites. It was found that the BST nanoparticles sized 32–40 nm were dispersed homogeneously in the polyimide matrix without aggregation. The ζ potential of PI/BST 33 vol.% was decreased in contrast with that of the pure polyimide. The coefficient of thermal expansion (CTE) of PI/BST 33 vol.% was measured between 36°C and 600°C. CTEs comparison showed about 80% decrease in the CTE value of the nanocomposite in respect to the pure polyimide in a wider temperature range.

Polyimide/Poly(ethylene terephthalate) Composite Membrane by Electrospinning for Nonwoven Separator for Lithium-Ion Battery

The polyamic acid (PAA), which is the precursor of polyimide (PI), is synthesized by pyromellitic dianhydride (PMDA) and 4, 4′-oxidianiline (ODA). The PAA/PET composite membrane is prepared with poly (ethylene terephthalate) (PET) nonwoven by electrospinning of the solution of PAA. The final PI/PET composite membrane is obtained after a thermal imidization process. The porosity, liquid electrolyte uptake and room temperature ionic conductivity of PI/PET composite membrane decreases a little comparing with PI membrane, but the tensile strength of PI/PET composite membrane increases more than PI ones. The experiments demonstrate that the diameter of the fibers decrease with the increase of the electrospinning voltage. At the same time, the decrease of the fibers diameter leads to the increase of the porosity as well as the liquid electrolyte uptake of the PI/PET composite membranes. As a result, the room temperature ionic conductivity is enhanced from 0.451 to 0.897 mS·cm−1. The PI/PET composite membrane shows only about 2% of thermal shrinkage at 180°C under air atmosphere. The cell with the PI/PET composite membrane shows stable cycling performances and better rate capabilities than the cells with the Celgard one under 10 C-rate.

Synthesis, characterization and hydrolytic stability of poly (amic acid) ammonium salt

A series of new poly (amic acid) ammonium salt (PAAS) precursors were prepared by incorporating different amounts of triethylamine (TEA) into terpolymer polyamic acid (PAA), which was synthesized by pyromellitic dianhydride (PMDA), 4,4’-oxydianiline (ODA) and p-phenylenediamine (PDA) in dimethylacetamide (DMAc). Then, the PAAS films were made by casting their solutions onto glass plates followed by the evaporation of the solvent. The chemical structure of PAAS films was confirmed by 1H NMR and FTIR spectroscopy. Mechanical properties, intrinsic viscosities and solubility of PAAS precursors were examined, respectively. It was found that the intrinsic viscosity of PAA solution obviously decreased with storage time during 30 days, while no distinct changes were observed in the intrinsic viscosity of the PAAS (the mole ratio of TEA/repeating unit of PAA = 2/1) solution after 90 days. The results suggested that hydrolytic stability of the PAAS films was significantly improved as compared with that of PAA film due to the polyelectrolyte structure of PAAS. Moreover, the thermal and mechanical properties of polyimide (PI) films prepared from PAAS precursors were also investigated, respectively.

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.