Poly Amic Acid Research Articles

Highly elastic and robust hydroxyapatite nanowires/polyimide composite aerogel with anisotropic structure for thermal insulation

Advanced composite aerogel materials have attracted much attention due to the unique structure and properties. However, the efficient manufacturing process and structural stability were still a challenge. Herein, a novel hydroxyapatite nanowires/polyimide (HAnws/PI) composite aerogel was synthesized by the ultralong HAnws combined with polyamic acid via directional freezing and thermal imidization. Among them, the HAnws and PI intertwined to form a three-dimensional network structure, which decreased the volume shrinkage of aerogel in thermal imidization from 42.9% to 12.6%, resulting in high porosity (>96%) and low density (0.0329–0.0431 g cm−3). In addition, the HAnws/PI aerogel with layered porous structure exhibits obvious anisotropic mechanical properties. The axial specific modulus as high as 78.05 kN m kg−1 and radial high elasticity can withstand 100 cycles of fatigue resistance. Moreover, the lowest radial thermal conductivity at 32.21 mW m−1 K−1 and the maximum of the anisotropy factor was 2.2, which was very suitable for insulation pipes to prevent additional heat loss. Therefore, the novel nanofibers reinforced organic aerogel was expected to provide more abundant functional applications in energy efficiency.

Effects of pre-imidization on rheological behaviors of polyamic acid solution and thermal mechanical properties of polyimide film: an experiment and molecular dynamics simulation

Effects of pre-imidization on rheological behaviors of polyamic acid solution and thermal mechanical properties of polyimide film: an experiment and molecular dynamics simulation

Thermal Conversion of Polyamic Acid Gel to Polyimide Solution Having Amino Group Sidechains

Thermal Conversion of Polyamic Acid Gel to Polyimide Solution Having Amino Group Sidechains

APPLICATION OF PIEZOSENSORS BASED ON THE MOLECULARLY IMPRINTED POLYIMIDE FOR DETERMI-NATION OF CAFFEINE IN TEA

In this article the molecularly imprinted polymers (MIPs) have been synthesized on the surface of piezosensors. The starting polymer for MIPs production was polyamic acid, which is a copolymer of 1,2,4,5-benzenetetracarboxylic acid and 4,4′-diaminodiphenyl ether. The caffeine served as the template. The quantum-chemical simulation was performed by the Gaussian 09 software using the DFT method at the B3LYP/6-31G(d,p) level with the basis set superposition error (BSSE) at the preliminary stage of the synthesis of the MIP for caffeine. The prepolymerization complexes were calculated to establish intermolecular interactions and obtain the optimum molar ratio between the template and polyamiс acid. It is shown that the constitutional repeating units of polyamic acid interact with the caffeine by forming H-bonds via carboxyl groups. The interaction energy first increases and then decreases with increasing the molar ratio of imprinting. Based on the quantum-chemical calculations, the optimal ratio of the reagents in prepolymerization mixture was set to 1 : 3 with the highest interaction energy (96.7 kJ/mol). Applying thermal imidization of solution of polyamic acid in the presence of a template, the molecularly imprinted polyimide has been synthesized by the non-covalent imprinting method. The ability of the obtained piezosensors to recognize the tempalte in model mixtures was experimentally evaluated. It was found that the range of detectable concentrations of caffeine is 3.1.10-6-10-1 mol/dm3 and the detection limit is 10-6 mol/dm3. Correctness of the caffeine determination in model solutions was verified in the spike/recovery tests. Piezosensors based on MIP were approved for the determination of the caffeine in tea varieties. It is shown that the concentration of caffeine in the aqueous solution increases with increasing brewing time. The relative standard deviation is less than 8%.

Preparation and Properties of Electrospun Phenylethynyl-Terminated Polyimide Nano-Fibrous Membranes with Potential Applications as Solvent-Free and High-Temperature Resistant Adhesives for Harsh Environments.

High-temperature-resistant polymeric adhesives with high servicing temperatures and high adhesion strengths are highly desired in aerospace, aviation, microelectronic and other high-tech areas. The currently used high-temperature resistant polymeric adhesives, such as polyamic acid (PAA), are usually made from the high contents of solvents in the composition, which might cause adhesion failure due to the undesirable voids caused by the evaporation of the solvents. In the current work, electrospun preimidized polyimide (PI) nano-fibrous membranes (NFMs) were proposed to be used as solvent-free or solvent-less adhesives for stainless steel adhesion. In order to enhance the adhesion reliability of the PI NFMs, thermally crosslinkable phenylethynyl end-cappers were incorporated into the PIs derived from 3,3’,4,4’-oxydiphthalic anhydride (ODPA) and 3,3-bis[4-(4-aminophenoxy)phenyl]phthalide (BAPPT). The derived phenylethynyl-terminated PETI-10K and PETI-20K with the controlled molecular weights of 10,000 g mol−1 and 20,000 g mol−1, respectively, showed good solubility in polar aprotic solvents, such as N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc). The PI NFMs were successfully fabricated by electrospinning with the PETI/DMAc solutions. The ultrafine PETI NFMs showed the average fiber diameters (dav) of 627 nm for PETI-10K 695 nm for PETI-20K, respectively. The PETI NFMs showed good thermal resistance, which is reflected in the glass transition temperatures (Tgs) above 270 °C. The PETI NFMs exhibited excellent thermoplasticity at elevated temperatures. The stainless steel adherends were successfully adhered using the PETI NFMs as the adhesives. The PI NFMs provided good adhesion to the stainless steels with the single lap shear strengths (LSS) higher than 20.0 MPa either at room temperature (25 °C) or at an elevated temperature (200 °C).

The effect of poor solvent on the microstructures and thermal insulation performance of polyimide aerogels

The sol–gel process is essentially a process of phase separation between micelles and solvent, so the influence of solvent composition on the result of phase separation will further affect the wet gel and the structure of the aerogel made by it. In this study, during the preparation of polyimide (PI) aerogels, poor solvents were introduced into the reagent during the synthesis of PI aerogel precursor, polyamic acids. The pore structure and thermal insulation performance changes of the PI aerogels caused by this behavior were studied. With the addition of poor solvent, submicron-scale pores were found inside the aerogel. In addition, the introduction of a small amount of poor solvent improved the thermal insulation performance of the prepared PI aerogel.

Largely improved dielectric properties of polyimide composites by tuning content and formation of CsPbBr3 nanocrystals

High dielectric constant polymer composites have considerable potentials in energy storage and dielectric applications because of simple fabrication process, facile processability, light-weight, excellent thermal stability and mechanical properties. Perovskite (CsPbBr3)/polyimide (PI) composites were successfully prepared via an in-situ polymerization from CsPbBr3 precursor in polyamic acid, followed by thermal imidization. The dielectric properties of polyimide composites were controlled by adjusting the content of CsPbBr3 nanocrystals. The obtained CsPbBr3/PI composites not only possess a high dielectric constant of up to 25.5 but also exhibit low dielectric loss below 0.25. The maximal discharging energy density reached up to 3.10 J cm−3 with 10% CsPbBr3, which is almost 3 times greater than pure PI under the same conditions. In addtiton, outstanding thermal properties of 5% decomposition temperature beyond 530 °C and good mechanical properties. The CsPbBr3/PI composites can be prepared facilely and rapidly on a large scale, which will be a outstanding dielectric material for high temperature polymer film capacitors.

Paper bacterial battery based on polymer as degradable sources of energy

Paper bacterial battery (PBB) is a sustainable source of bioenergy derivate from bacterial activities, paper bacterial battery or microbial fuel cell has unique features like biodegradable, cost- affordable, energy- effectiveness, and environmental sounds beside of complete control by produced energy by increasing the number of folds and can made it in shapes and sizes appropriate for all use and type of devices, which is characterized by high flexibility and wide uses. The current study described in detail the fabrication steps of a simply biodegradable paper battery that mainly composed of a substrate of cellulose, Poly (amic) acid (PAA) and polyvinyl alcohol (PVA) as reducing and stabilizing agent, immobilization matrix, for bacterial cells stability, this degradable network provides oxygen-blocking and proton exchange membrane (PEM). The fabricated bacterial battery gave power of 3.5 µW/cm2 and a current quantity of 127 µA/cm2, this generated power can be enhancement by more folding or compacting of the fabricated paper-polymer unit. Â

Nanopore engineered tortuosity towards thermo-mechanically enhanced low-k polymer-mesoporous organosilica composite membranes

The continuous development of microelectronics requires mechanically enhanced insulating materials with a lower dielectric (low-k) constant. To accomplish this, in this paper, low-k polymer nanocomposites were reinforced with hydrophobic ethane-bridged mesoporous organosilica (EMO) particles as fillers. In this study, three types of EMOs such as pure EMO, EMO functionalized with trimethoxyphenylsilane (PTS) (EMO-PTS) group, and EMO functionalized with 1-[3-(trimethoxysilyl)propyl]urea (UTS) (EMO-UTS) group were prepared via sol-gel self-assembly method. Mesostructures and surface areas of synthesized EMO particles were successfully characterized by XRD, TEM, and BET, whereas 13C and 29Si CP/MAS NMR spectra were also evidenced the presence of organic functional groups in the final EMO particles. Then, these filler materials were employed along with PMDA-ODA PAA (polyamic acid) solution for making efficient polyimide (PI) polymer composites. The good dispersion of EMO/EMO-PTS/EMO-UTS fillers into polyimide (PI) matrix were investigated using cross-section of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atom force microscopy (AFM). UV–visible spectroscopy has also shown optical transmittance more than 80% in the visible range. Dielectric constant (DC) was also found to be reduced from 3.42 (in PI) to 2.51 (in polymer composites) upon addition of 2–3 wt% of filler materials. The addition of these fillers into polymer PI has also significantly enhanced modulus, hardness and glass-transition temperature of the final composites. These results strongly suggest that EMO and functionalized EMO with either PTS or UTS could be used as promising “reinforcing mesoporous filler and low-k materials” with polyimide.

Polyimide-Derived Carbon-Coated Li4Ti5O12 as High-Rate Anode Materials for Lithium Ion Batteries.

Carbon-coated Li4Ti5O12 (LTO) has been prepared using polyimide (PI) as a carbon source via the thermal imidization of polyamic acid (PAA) followed by a carbonization process. In this study, the PI with different structures based on pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) moieties have been synthesized. The effect of the PI structure on the electrochemical performance of the carbon-coated LTO has been investigated. The results indicate that the molecular arrangement of PI can be improved when the rigid p-PDA units are introduced into the PI backbone. The carbons derived from the p-PDA-based PI show a more regular graphite structure with fewer defects and higher conductivity. As a result, the carbon-coated LTO exhibits a better rate performance with a discharge capacity of 137.5 mAh/g at 20 C, which is almost 1.5 times larger than that of bare LTO (94.4 mAh/g).

Sol-gel transition of polyamic acid solution during chemical imidization and its effect on the drawing behavior of polyimide films

Herein, sol-gel transition of 3,3′,4,4′-biphenyldianhydride (BPDA)/p-phenylene diamine (PDA) polyamic acid (PAA) solution were investigated by adding excessive dehydration reagent, and it was found that increasing the amount of dehydration reagent and pyridine content, as well as the temperature could accelerate the sol-gel transition. The maximum strain of PAA film at the gel stage of sol-gel transition increases from 1.5 to 5.8 compared to the pure PAA film, and the better drawing property enables it has the potential to prepare PI films with more excellent mechanical properties and lower coefficient of thermal expansion (CTE). When the solvent content of PAA gel film increases from 20% to 85%, the tensile strength and modulus of the corresponding PI film with a draft ratio of 1.5 increase from 488 MPa to 12.1 GPa to 591 MPa and 17.3 GPa, respectively. Therefore, the PI film drawn from the gel film with higher solvent content has better mechanical properties. Besides, the corresponding amorphous and orientation composite models with different solvent content were constructed and analyzed based on molecular dynamic (MD) simulation. The FFV of amorphous composite model decreases with the decrease of solvent content, indicating that the model with higher solvent content has less intermolecular entanglement and interaction during the drawing process. The mean square end-to-end distance and XRD patterns demonstrate that the molecular chain in the orientation model drawn from the amorphous model with higher solvent content have more regular and extended arrangement along the drawing direction. Accounting for the reason that PI film drawn from the gel film with higher solvent content exhibits more excellent mechanical properties.

A Study on the Interfacial Compatibility, Microstructure and Physico-Chemical Properties of Polyimide/Organically Modified Silica Nanocomposite Membrane.

Polyimide-silica (PI-Silica) composites are of tremendous research interest as high-performance materials because of their excellent thermal and mechanical properties and chemical resistance to organic solvents. Particularly, the sol-gel method of fabricating such composites is popular for manipulating their properties. In this work, PI-silica composite films are synthesized by the sol-gel method and thermal imidization from the solution mixtures of hydrolyzed tetraethoxysilane (TEOS) (or glycidoxypropyltrimethoxysilane (GPMS)) modified silica and an aromatic polyamic acid (PAA) based on 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA)–p-phenylenediamine (PDA). The phase morphology of composites is found to be controlled by the substitution of TEOS with GPMS. Solid-state NMR spectroscopy is used to confirm the structural components of silica and GPMS-modified silica, whereas FT-IR results confirm the complete imidization of polyimide and composite film and suggest successful incorporation of Si–O–Si bonds into polyimide. The thermal, optical transmittance, and dielectric constant characterizations of pure polyimide and composite films are also carried out. Thermal stability of pure polyimide is found to be increased significantly by the addition of silica, whereas the partial substitution of TEOS with GPMS decreases the thermal stability of the composite, due to the presence of the alkyl organic segment of GPMS. The optical transmittance and dielectric constant of the composite films are controlled by manipulating the GPMS content.

Facile strategy to prepare polyimide nanofiber assembled aerogel for effective airborne particles filtration

Polyimide nanofiber (PINF) aerogel materials have received extensive attention as heat insulation, sensors and filtration media due to their excellent thermodynamic properties and unique porous structure. However, PINF must be difficult to disperse in organic solvents (dioxane or dimethyl sulfoxide) and dimensional instability has been regarded as issues that limits the preparation of PINF aerogels, especially in the water. So, it is of great significance to prepare polyimide aerogels with stable structure using water as a dispersant. In this work, the electrospun polyimide nanofiber precursor (polyamic acid (PAA) nanofiber (PAANF)) is uniformly dispersed in water, and triethylamine is added to terminated PAA oligomer as a binder. The resultant PINF aerogel has excellent mechanical properties with outstanding elasticity and a maximum compressive stress of 7.03 kpa at 50% strain. Furthermore, due to the extremely high porosity (98.4%) and hierarchical porous structure, the aerogel exhibits a high filtration efficiency (99.83%) for PM2.5, while the pressure drop is lower than that of the corresponding nanofiber membrane materials, which will facilitate its application in high temperature filtration and other fields.

Preparation and Characterization of PTFE/PI Nanofiber Composite Assembled Sponges

Due to the ultralow density and high specific area, nanofibrous sponges show great potential in the field of filtration and separation. To prepare nanofibrous sponges for high temperature smoke filtration, polytetrafluoroethylene (PTFE) was chosen due to its corrosion resistance and high temperature resistance. PTFE nanofiber prepared via electrospinning shows irregular concave-convex pores in the fiber body, which can improve the specific surface area and further enhance filtration performance. However, sponges made of PTFE nanofiber suffered from severe shrinkage, which limited the development in sponge products. In this study, polyimide (PI) nanofiber converted from polyamic acids (PAAs) nanofiber was introduced into the PTFE sponges to reinforce the dimensional stability. The parameters that influenced the morphology, porosity, shrinkage ratio, and thermodynamic properties of the composite sponges were also investigated. Moreover, the filtration performance of the composite sponges was tested. Results indicated that PTFE/PI composite nanofiber sponges possessed high porosity (94.34–98.12 %), excellent thermal stability (above 550 °C), and decent filtration efficiency (the maximum filtration efficiency reached 99.97 % to PM 2.0) were prepared, which demonstrated the potential in the field of high-temperature filtration.

Fabrication of Porous Polyimide Membrane with Through-Hole via Multiple Solvent Displacement Method.

Porous polyimide (PI) membranes are widely used in separation processes because of their excellent thermal and mechanical properties. However, the applications of porous PI membranes are limited in the nanofiltration range. In this study, porous PI membranes with through‐holes have been successfully fabricated by the novel multiple solvent displacement method. This new method requires only a porous polyamic acid (PAA) membrane, which was prepared by immersing PAA film in N‐methylpyrrolidoneebk; (NMP) prior to immersing it in a mixed solvent consisting of NMP and a poor solvent, followed by immersion only in poor solvent. The pore size, morphology, porosity, and air permeability demonstrated that the fabricated PI membranes had a uniformly porous structure with through‐holes over their surface. This new method enabled control of pore size (3–11 μm) by selecting a suitable poor solvent. This multiple solvent displacement method is highly versatile and promising for the fabrication of porous PI membranes.

Improving dimensional stability at high temperature and toughness of polyimide films via adjustable entanglement density

Polyimide (PI) films with ultralow coefficient of thermal expansion (CTE) and high glass transition temperature (Tg) are in great demand for applications as substrates in flexible displays. Furthermore, trade-off between CTE and toughness is highly concerned due to strategies for reducing CTE always result in weakness of toughness. In this work, we developed a facile method to improve dimension stability and toughness of PI containing benzimidazole units via regulating entanglement density based on controlling molecular weight and solid content of precursor polyamic acid (PAA) solution. As a result, the Tg of PI films increased from 394.3 to 441.4 °C and the in-plane CTE (40–350 °C) decreased from 65.7 to 3.9 ppm/K with entanglement density increasing from 253.3 to 2868.6 mol/m3. Moreover, mechanical properties especially toughness of PI films were enhanced significantly (from 7% to 18%) as entanglement density increased. In short, we delineated the effects of entanglement on the properties of PI films and found that the decrease of CTE mainly arises from the increase of entanglement density. Our studies provide new insights into the future design of flexible PI substrates with low CTE.

Combing three-dimensional water channels and ultra-thin skin layer enable high flux and stability of loose polyimide/SiO2 nanofiltration membranes at low operating pressure via one step in-situ modification

Desalination of brackish water and purification of drinking water still pose several challenges. Combination of in-situ hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in polyamic acid (PAA) solution along with imidization reaction provide a novel polyimide/SiO2 (PI/SiO2) membrane. This is the first synthesis of a PI nanofiltration (NF) membrane with three-dimensional (3D) water channels, ultra-thin skin layer (30 ± 2 nm), and high flux at low operating pressure, by one-step phase inversion method. There was no additional requirement of an acid, since PAA served as a catalyst. The SiO2 cross-linked network provided the skeletal support, due to hydrogen bonding between PAA-PI and silicon hydroxyl groups. The fabricated PI/SiO2 membrane demonstrated a water contact angle of 45°, pore size of 1.05 ± 0.15 nm, Zeta potential of −30 mV, and tensile strength of 2.24 MPa when under optimized conditions. The loose PI/SiO2 NF membrane exhibited salt rejection in the sequence of Na2SO4 (87%)>MgSO4 (67%)>NaCl (41%)>MgCl2 (37%), which was consistent with size exclusion and Donnan exclusion effects. In particular, the water flux of 20.4 L/(m2 h bar) was about 4–15 times higher than that of universal PI-NF membranes. The membrane also exhibited excellent stability for over six days when used for separation. Furthermore, the membrane showed excellent dye (Rose Bengal (RB), Brilliant Blue G (BBG), Amido Black (AB)) rejection of over 90%. To conclude, this work paves a new pathway for the fabrication of PI-NF membranes for efficient NF separation.

Novel 3D-networked melamine–naphthalene–polyamic acid nanofillers doped in vinyl ester resin for higher flame retardancy

In this study, melamine–naphthalene covalent polyamic acid and its metal carboxylate salts were synthesized as building blocks of nanofillers (Nt–Mn–PA–COOM, M = Li, Na, and K).

Synthesis and Thermal Properties of Polyamic Acids and Its Six-Membered Cyclic Polyimides from Ethylenediaminetetraacetic Acid

Synthesis and Thermal Properties of Polyamic Acids and Its Six-Membered Cyclic Polyimides from Ethylenediaminetetraacetic Acid

Highly solvent-durable thin-film molecular sieve membranes with insoluble polyimide nanofibrous substrate

Permselective thin-film composite membranes are gaining a significant role in solvent-based molecular sieving applications. Nevertheless, the lack of desirable substrate materials, which combines high flux, solvent resistance as well as a straightforward fabrication process, is still the biggest bottleneck for large-scale commercial implementation. For the first time, we propose to fabricate an insoluble polyimide nanofibrous substrate by a sequential strategy involving electrospinning polyamic acid followed by a thermal imidization. The water-absent electrospinning process leads to 1-fold enhanced mechanical strength and higher solvent-resistance of substrate compared to the conventional phase inversion process. The resultant thin-film nanofibrous composite (TFNC) membranes exhibit exceptional potential for nanofiltration by showing high permeability, rejection, and stability in water as well as polar aprotic solvents such as dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran compared to state-of-art membranes. The strategy of using electrospun insoluble polyimide as the substrate establishes a scalable approach to design high-performance TFNC membranes for a wide range of challenging molecular sieving applications.