Linear Polyimide Research Articles

Donor-acceptor hyperbranched copolyimides contain different linear segment for electrochromic and resistive memory devices

In this work, two hyperbranched copolyimides (O-coPI and F-coPI) were synthesized which the diamine donors in the linear segment contain different substituents. To investigate the effects of substituents in donors on their memory behavior, the corresponding linear polyimides (F-LPI and O-LPI) were also discussed. The devices based on hyperbranched copolyimides exhibited non-volatile write once read many times memory (WORM) behavior, while the devices based on linear polyimides exhibited volatile memory dynamic random-access memory (DRAM) behavior. Polyimides (O-coPI and O-LPI) prepared with methoxy-substituted diamine donors have low switching voltages due to their good electron-donating properties. In addition, O-coPI and O-LPI also exhibit electrochromic properties. Hyperbranched copolyimide O-coPI have higher optical contrast and faster response time than that of linear polyimide O-LPI. This work provides a new direction for the development of multifunctional memory materials.

Molecular dynamics study on the mechanism of poly(amic acid) chemical structure on thermal imidization process and polyimide architecture

In this work, the thermal imidization of 3,3′, 4,4′-biphenyltetracarboxylic dianhydride/p-phenylenediamine (BPDA/PDA), pyromellitic dianhydride/4,4′-oxydianiline (PMDA/ODA), 4,4′-oxydiphthalic anhydride/4,4′-oxydianiline (ODPA/ODA), and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride/2,2′-bis(trifluoromethyl)benzidine (6FDA/TFMB) polyimides (PIs) were investigated based on molecular dynamics (MD) simulation. It was found that two kinds of imide bonds were formed, i.e., inter-molecular and intra-molecular imide bonds, which results in differences in the final architecture of the target PI systems. The BPDA/PDA and PMDA/ODA PIs present crosslinking network structure, while the ODPA/ODA PI shows a hybrid structure composed of crosslinking and linear fragments, and the 6FDA/ODA PI displays linear and branched structures. Compared with the previous view of linear PI molecular chains, these results agree well and better account for the thermoset of PMDA/ODA and BPDA/PDA, thermoplasticity of ODPA/ODA, and solubility of 6FDA/TFMB. The mechanism causing the above differences was studied from radial distribution function (RDF), coordination number, fractional free volume (FFV), and density field analysis. By comparing the experimental and simulated values of glass transition temperature and modulus of PI models, the rationality of inter-molecular imide bonds is proved. In addition, through the PAA/DMF compound models, it was found that the increase of solvent content hindered the formation of inter-molecular imide bonds. This study provides new insights into the thermal imidization process and the final architecture of PIs derived from poly(amic acid).

The crystalline linear polyimide with oriented photogenerated electron delivery powering CO2 reduction

Orienting electron transport to suppress charge recombination is attractive for efficient photocatalysis but remains challenging. Herein, we demonstrate the synthesis of crystalline linear conjugated polyimides via the condensation of carboxylic anhydrides and amine monomers for the photocatalytic reduction of CO2. Oriented electron transport was achieved using crystalline polyimides integrated with electronic push-pull units. Directional intramolecular electron transfer is driven by the dipole effects of the adjacent building units. The sulfone-based polyimide exhibited excellent photocatalytic performance for CO2 reduction. Our work provides a new example photoreduction of CO2 and a strategy for developing efficient photocatalysts with oriented electron transport.

Preparation of Optically Active Polyimides Based on 2,2´-diamino-1,1´-binaphthalene

Linear polyimides based on both of the 2,2´-diamino-1,1´-binaphthalene enantiomers and their racemic mixture were synthesized and characterized. A two-step synthetic route, consisting of the preparation of the polyimide precursor followed by its thermal imidization at temperatures not exceeding 200°C, was employed. The products were analyzed by FTIR and 1H NMR spectroscopy. All of the tested materials were nearly fully imidized after 25 h. The final polyimides possess high glass transition temperatures, are thermo-oxidatively stable and are soluble in common organic solvents as 1-methyl-2-pyrrolidone, tetrahydrofuran and chloroform; additionally, those prepared from the enantiomers show optical activity. The values of specific optical rotations for the polymers were higher than those for the corresponding monomers. However, the directions of their optical rotations were identical. Due to their rather low molar masses, the final polyimides form brittle self-standing films. Thin layers of these products on porous polyimide substrates were made under forming composite membranes.

Crosslinked Polyimides as Cathodes for Lithium-Ion Batteries

Organic cathode materials for lithium-ion batteries are becoming increasingly popular because of their structural flexibility, resource abundance, and environmental friendliness. However, their application is limited by their solubility in electrolytes, which leads to the rapid decay of cycling performance. Herein, we synthesize crosslinked polyimides by condensation polymerization between 3,4,9,10-perylenetetracarboxylic dianhydride and 1,2-ethanediamine in the presence of a trifunctional crosslinker of diethylenetriamine. The synthesized crosslinked polyimides present a porous structure with a high surface area. The crosslinked polyimide cathode materials used in lithium metal half-cells have a high discharge capacity of 160.3 mA h g–1 at a current density of 30 mA g–1, and the assembled lithium-ion batteries maintain 77% capacity after 2000 cycles at a current density of 150 mA g–1, which is much better than that of lithium-ion batteries employing linear polyimides, demonstrating that crosslinked polyimides may be potential cathode materials for high-performance lithium-ion batteries.

Fabrication of high-surface-area, SiO2 supported polyimide carbon aerogel microspheres: electrochemical application

A series of polyimide (PI)/SiO2 aerogel microspheres were prepared by using polyamide acid salt and hydrolyzed tetraethyl orthosilicate based on the reverse-phase emulsion method. Then, PI/SiO2 aerogel microspheres were carbonized and etched to obtain carbon aerogel microspheres (CAMs). Scanning electron microscope, transmission electron microscope and nitrogen isothermal adsorption were used to characterize the micro-morphology and pore structure of the microspheres; and electrochemical workstation was used to test the electrochemical performance of the CAMs. The results showed that CAMs with different pore structures and specific surface area were obtained by adjusting the content of SiO2. Highest specific surface area of 1166.9 m2 g−1 and a total pore volume of 1.2369 cm3 g−1 were achieved at a SiO2 content of 50%. When used as the electrode materials for supercapacitors, these CAMs demonstrated a maximum specific capacitance of 125.1 F g−1 in a three-electrode system and a maximum capacitance of 53.3% at 30 A g−1. This article provides a new strategy for the preparation of CAMs with high specific surface area by using linear PI precursor and SiO2 support skeleton.

Rigid/flexible molecular structure‐induced polyimide aerogels with ultralow permittivity and thermal insulation properties

AbstractA series of high‐performance linear and cross‐linked polyimide (PI) aerogels with different molecular structures have been successfully synthesised using the freeze‐drying process. In this study, the comprehensive regulation of microstructure, thermodynamic, thermal insulation and dielectric properties of PI aerogels are achieved by controlling the rigid/flexible structure and composition of polymerised monomers. The increase in rigidity of PI molecular structure could promote the formation of denser pores, which is beneficial to improve the thermodynamic and thermal insulation properties of aerogels. Notably, the cross‐linked PI aerogel prepared by introducing cross‐linking agent (tris(4‐aminophenyl) amine, [TPA]) into linear PI exhibits high thermal stability (Td5% > 560°C), excellent ultralow permittivity (εr = 1.31, f = 106 Hz) and good thermal insulation property (k = 0.056 W/m · K). This innovative strategy promotes the wider application of the cross‐linked polyimide aerogel in the field of integrated circuits and aerospace exploration.

Microporous Matrimid/PIM-1 Thin Film Composite Membranes with Narrow Pore Size Distribution used for Molecular Separation in Organic Solvents.

Polymers of intrinsic microporosity (PIMs) are a class of microporous organic materials that contain interconnected pores of less than 2nm in diameter. Such materials are of great potential used in membranes for molecular separation, such as drug fractionation in pharmaceutical industry. However, the PIMs membranes are often susceptible to low separation selectivity toward different molecules due to their wide pore size distribution. Herein, a linear polyimide, Matrimid, is incorporated with PIM-1 (a typical member of PIMs) by solution blending, and the blends are dip-coated onto a polyimide P84 support membrane to prepare thin-film composite (TFC) membranes to control pore size distribution while keep high microporosity. The component miscibility, pore characteristics, and molecular separation performances of the Matrimid/PIM-1 TFC membranes are investigated in detail. The Matrimid and PIM-1 are partially miscible due to their similar Hansen solubility parameters. The Matrimid endows the selective layers (coatings) with narrower pore size distribution due to more compact chain packing. The prepared Matrimid/PIM-1 TFC membranes show high selectivity for separation of riboflavin (80% of retention) and isatin (only 5% of retention). The developed membranes exhibit great potential for separating molecules with different molecular weights.

Microporous polyimide networks with tunable micropore size constructed through side-chain engineering of linear precursors

Microporous polyimides (MPIs) have been acted a significant role in porous organic polymers (POPs) for gas capture and separation. However, the MPIs are mostly constructed from monomers with rigid 3D or twisted structures or hyperbranched precursors, and their porous structure is mainly tuned by changing the length of the constructed units. Herein, the cross-linkable linear PIs with flexible skeletons are selected as precursors to construct the cross-linked microporous polyimides (C-MPIs). The method has significant comparative advantages including abundant monomers, the convenience of synthesis, cost-effectiveness, structural diversity and designability. Moreover, the micropore size of the C-MPIs (6FA-PE-CL, 6FA-PEPH-CL) can be tuned from 0.64 nm to 0.57 nm through the side-chain engineering of the cross-linkable linear PI precursors. The BET surface area of the C-MPIs are ranging from 635 to 698 m 2 g -1 and is among the best results for the reported linear MPIs. The smaller pore size (0.57 nm), higher micropore surface area (378 m 2 g -1 ) and micropore volume (0.17 cm 3 g -1 ) endow 6FA-PE-CL with better CO 2 selective uptake capacity (8.9 wt% and 58) than those of 6FA-PEPH-CL (7.3 wt% and 38). This work provides a side-chain engineering method to tune the pore structure of MPIs, which has tremendous potential for constructing high-performance polymer networks with abundant ultramicroporous structure (<0.7 nm) based on flexible linear polymers. Microporous polymer networks with tunable micropore sizes have been constructed through the side-chain engineering of cross-linkable linear polyimide precursors. • The microporous polymer networks with abundant ultramicropores were constructed from flexible linear polyimides. • The pore size can be finely tuned through the side-chain engineering method. • The microporous polyimide with a smaller pore size exhibits better CO 2 selective uptake capacity.

Optically active polyimides with different thermal histories of their preparation.

Optically active linear polyimides and hyperbranched poly (amic acid-imide) were prepared by using procedures varying in particular in the maximum temperature employed in their synthesis. The two types of linear polyimides were based on 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 1,2-diaminocylohexane enantiomers or 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 2,2'-diamino-1,1'-binaphthalene enantiomers. The amine-terminated hyperbranched poly (amic acid-imide) was prepared from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 4,4',4″-triaminotriphenylmethane, and its end groups were modified with the chiral selectors N-acetyl-D-phenylalanine or N-acetyl-L-phenylalanine. The final structure of the products was analyzed by IR spectroscopy, and their optical activity was evaluated and confirmed by polarimetry or circular dichroism.

Hierarchically nanostructured carbon nanotube/polyimide/mesoporous Fe2O3 nanocomposite for organic-inorganic lithium-ion battery anode

Integrating organic multiple-carbonyl polymers and inorganic mesoporous metal oxides on highly conductive carbon nanotubes is a promising strategy to manufacture high-performance lithium-ion battery anodes; however, developing multicomponent nanocomposites with a hierarchical architecture still remain challenging. Herein, we design and produce hierarchically nanostructured carbon nanotube (CNT)/polyimide (PI)/mesoporous Fe 2 O 3 (meso-Fe 2 O 3 /PI/CNT) ternary nanocomposite materials via a sequential assembly and high-temperature dehydration strategy, aiming to fabricate flexible PI-supported meso-Fe 2 O 3 stacked on a conductive CNT supporting skeleton. By controlling the linear PI mainchain through the comonomer composition, different PI assemblies can grow on the surface of CNT to anchor meso-Fe 2 O 3 nanoparticles as well as alleviate the structural strain resulting from the volume expansion of meso-Fe 2 O 3 in its phase conversion reaction. Considering the porosity and cavity, the mesoporous Fe 2 O 3 architecture can not only buffer its volume expansion but also accommodate a large number of electrolytes to promote Li + transport. In addition, the hierarchical architecture endows the meso-Fe 2 O 3 /PI/CNT nanocomposite materials with a high structural stability during the electrochemical process. Benefiting from these structural advantages, Li-ion batteries assembled with meso-Fe 2 O 3 /PI-EDA/CNT electrodes deliver high capacities of 708.9, 608.2, and 454.5 mAh g −1 at 0.1, 0.3, and 0.5 A g −1 , respectively. Even at a high current density of 1 A g −1 , a discharge capacity of 95.6 mAh g −1 is still obtained after 3000 cycles. This work provides a promising route to integrate multiple-carbonyl polymers and mesoporous metal oxides with the aim of developing multicomponent organic-inorganic composite anode for Li-ion battery. • Hierarchically tubular organic-inorganic nanocomposite anode from self-assembly-assisted fabrication technique is reported. • Polyimide assemblies with controllable architecture for organic anode material and strain buffer interlayer. • Fe 2 O 3 nanoparticle with mesoporous structures for inorganic anode material. • The organic-inorganic nanocomposite anode shows desirable lithium-ion battery performance.

Investigation of ion-electrode interactions of linear polyimides and alkali metal ions for next generation alternative-ion batteries.

Organic electrode materials offer unique opportunities to utilize ion-electrode interactions to develop diverse, versatile, and high-performing secondary batteries, particularly for applications requiring high power densities. However, a lack of well-defined structure–property relationships for redox-active organic materials restricts the advancement of the field. Herein, we investigate a family of diimide-based polymer materials with several charge-compensating ions (Li+, Na+, K+) in order to systematically probe how redox-active moiety, ion, and polymer flexibility dictate their thermodynamic and kinetic properties. When favorable ion-electrode interactions are employed (e.g., soft K+ anions with soft perylenediimide dianions), the resulting batteries demonstrate increased working potentials and improved cycling stabilities. Further, for all polymers examined herein, we demonstrate that K+ accesses the highest percentage of redox-active groups due to its small solvation shell/energy. Through crown ether experiments, cyclic voltammetry, and activation energy measurements, we provide insights into the charge compensation mechanisms of three different polymer structures and rationalize these findings in terms of the differing degrees of improvements observed when cycling with K+. Critically, we find that the most flexible polymer enables access to the highest fraction of active sites due to the small activation energy barrier during charge/discharge. These results suggest that improved capacities may be accessible by employing more flexible structures. Overall, our in-depth structure–activity investigation demonstrates how variables such as polymer structure and cation can be used to optimize battery performance and enable the realization of novel battery chemistries.

Highly polymerized linear polyimide /H3PW12O40 photocatalyst with full visible light region absorption

The degree of polymerization in polyimides has significant effects on their photoelectric properties. Increase the degree of polymerization in polyimide can improve its light absorption capability as well as reduce the recombination rate of photogenerated electrons and holes. However, it is difficult to promote the polymerization of polyimides by conventional approaches, such as increasing the polymerization temperature since polyimides are susceptible to high temperature and can be decomposed. In this paper, a suitable proportion of phosphotungstic acid was introduced to increase the degree of polymerization of polyimide at a lower polymerization temperature, so as to improve the light absorption capability of the composite and inhibit the recombination of electron and hole. The p-phenylenediamine based polyimide with the one-dimensional linear polymer chain has excellent charge transfer ability, so the POM-π effect formed with phosphotungstic acid is stronger, correspondingly, the light absorption capacity of the composite photocatalyst formed is stronger than that of the cross-linked polyimide/phosphotungstic acid.

Properties improvement of linear polyimide aerogels via formation of doubly cross-linked polyimide-polyvinylpolymethylsiloxane network structure

The properties of linear polyimide aerogels (LPAs) were improved by introducing the network structure of polyvinylpolymethylsiloxane (PVPMS) into that of LPAs. The formed doubly cross-linked polyimide (PI)-PVPMS network structure endowed samples with resilience and fire-retardant property. On the one hand, the PI-PVPMS composite aerogels (PPCAs) can recover to 20% of their own height rather than exhibit almost no resilience after compression. On the other hand, they can maintain high structural integrity instead of showing drastic volume shrinkage after prolonged burning. Moreover, our results showed that the introduced network structure of PVPMS not only weakened the effect of PI rigidity on the structural properties of LPAs, but also played a leading role in the physical properties of synthesized PPCAs. The obtained PPCAs with different PI rigidity exhibited similar microstructure and properties, which indicated that the lower cost monomers of PI could be selected to prepare PPCAs and promote the large-scale production.

Synthesis and enhanced CO2/CH4 selectivity of hyperbranched copolyimide membranes

A series of hyperbranched copolyimides (co-HBPIs), as the completely symmetrical tetraamine monomer successfully incorporated into the linear polyimide 6FDA-ODA, were synthesized under the chemical imidization after the gel formation was avoided, as to more effectively separate CO2/CH4. CO2/CH4 selectivity (74%) was observed to be improved significantly under 7‰ tetraamine contents at 2 bar and 35°C; thus, the acceptable CO2 permeability was maintained compared with the pure membrane, exceeding the 1991 upper bound. Moreover, the as-prepared membrane with 6FDA-ODA-7‰ was reported to exhibit higher CO2/CH4 selectivity (109.14) at 10 bar and 35°C. Accordingly, the hyperbranched copolyimides will be promising candidates as membrane materials for the further separation of CO2/CH4 gas pair.

Preparation of high-strength polyimide membranes capped by ionic liquids

In this study, we firstly used 1-carboxyethyl-3-methylimidazolium ionic liquid as a capping agent to terminate a binary linear polyimide containing different groups such as ether bonds, carbonyl groups, and fluorine, and prepared six kinds of polyimides capped with ionic liquids (IL-PI). The mechanical properties of the polyimide membranes capped with ionic liquids were higher than those of the uncapped polyimide membranes. The elastic modulus of polyimide membrane from 1,3-bis (4-aminophenoxy) benzene (BPDA) and 3,3′4,4′-benzophenone tetracarboxydianhydride (BTDA) by using ionic liquid as the end capping agent (IL-BPDA-BTDA) was 2012 MPa, which is about 70 times higher than that without the end capping agent. In a TG test, all polyimides capped by ionic liquids showed good thermal properties. The residual amount of the polyimides was more than 40% at 1000 °C, which was higher than the other uncapped polyimides. In conclusion, polyimide membranes with high temperature resistance and high mechanical strength were prepared through an ionic liquid termination method.

Chain structure-dependent electrochemical performance of polyimide cathode materials for lithium-ion batteries

Organic polyimides have received an ever-growing interest in lithium-ion batteries based on the reversible anion stabilization mechanism of redox-active carbonyl groups due to their high theoretical capacities, resource sustainability, and diverse chain structures. Herein, four linear polyimides with different chain structures were synthesized by a facile and green hydrothermal method. The chain structure-electrochemical performance relationship was explored by regulating active anhydride units and diamine linkers. The incorporation of flexible linkers between redox-active anhydrides results in the facile movement of polyimide chains and the formation of porous networks with abundant active sites. In contrast, rigid aromatic linkers with strong π–π conjugation tend to assemble into the orderly-stacked sheets, enabling the efficient electron transfer. When used as the battery cathode, 1,4,5,8-naphthalenetetracarboxylic dianhydride-based polyimide with a relatively flexible linker delivers the largest specific capacity. Such a polyimide also demonstrates the high cycling stability with a capacity retention up to 52% over 10000 cycles. In contrast, pyromellitic dianhydride-based polyimide with a benzene-enriched linker exhibits the lowest capacity and poor rate capability due to its densely-stacked sheets and limited exposure of active groups. The chain structure-dependent performance relationship of polyimides would offer new insights into the rational design of high-performance organic electrodes for the next-generation batteries.

Microporous polymer networks constructed from cross-linkable linear polyimides for CO2 adsorption

In recent years, linear polyimides of intrinsic microporosity have been widely used in the field of gas adsorption and separation because of their high BET surface area and microporous structures. Most of the microporous structures come from the twisted main-chain structures in the linear polyimides of intrinsic microporosity. Therefore, most linear polyimides (PI) without twisted structure have no porosity. Herein, to construct the linear polyimide with microporous structure, a sequence of microporous polyimides (PIs-CL) were constructed from the flexible linear polyimide precursors through the thermal crosslinking reaction. The polyimide precursors without twisted structure were synthesized from a well-designed diamine TFVBPA with cross-linkable ethynyl groups and several commercial dianhydrides (ODPA, BPDA, PMDA and 6FDA) by polycondensation to research the influence of the main-chain structure on the porous characters. The introduction of crosslinked structures gives the linear crosslinked polyimides (PIs-CL) with porous structures. The PIs-CL show obviously improved porosity (0.52–1.71 nm) and higher BET surface area (337–618 m2 g−1) than those of the uncrosslinked polyimides (PIs). Moreover, PIs-CL have favorable CO2 adsorption (5.7–9.3 wt%) as well as good CO2/N2 selectivity (34.4–58.5) at 273 K, which are better than other polyimides materials. The introduction of crosslinked structures is an effective way to improve microporous porosity and gas sorption performance.

Free volume manipulation of a 6FDA-HAB polyimide using a solid-state protection/deprotection strategy

Tert-butoxycarbonyl (t-BOC) is a thermally labile moiety that can be used to protect hydroxyl groups on polymers. In this study, t-BOC was appended onto a polyimide consisting of 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB), after which the polymer was formed into self-standing films. Solid-state thermal treatments were performed to systematically remove t-BOC moieties to alter the physical packing structure and concomitant gas transport properties of the polymer. Despite performing deprotection reactions well below the glass transition temperature of 6FDA-HAB (~300 °C), this free volume manipulation (FVM) approach produced only subtle differences in polymer density, fractional free volume, average free volume element size, and gas transport properties relative to the unprotected polymer. While these findings suggest that thermally removing covalently bound functional groups from polymer films can be used to manipulate free volume and gas transport performance for glassy polymers, more robust polymer systems than linear polyimides are required to preserve the nascent free volume architecture generated from this approach.

Chain engineering-tailored microstructures and lithium storage performance of hydrothermally-synthesized linear polyimides

Polyimides with high capacity, fast kinetics, abundant resource, and structural diversity offer an exhilarating opportunity for developing sustainable rechargeable batteries. Herein, a series of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA)-based polyimides were successfully crafted through a facile and eco-friendly hydrothermal synthesis route. The microstructure and lithium storage performance of polyimides were tailored by regulating diamine linkers between NTCDA units. Interestingly, the moderate increased length of flexible diamine units with ethylenediamine and diaminobutane can stabilize the polymer skeleton. This leads to the formation of honeycomb-like porous structures with a sufficient exposure of active carbonyl groups, thereby achieving a large capacity and high rate capability. Therefore, polyimides derived from ethylenediamine and diaminobutane show larger reversible capacities (123 and 113.5 mA h/g at 50 mA/g, respectively) and better rate capabilities with capacity retentions of up to 50% when the current increased from 50 to 2000 mA/g. This work would provide new insights into macromolecular engineering of polymers for advanced electrode materials.