Imide Structure Research Articles

Sustainable poly(imide‐imide) vitrimer based on multiple dynamic covalent bonds

AbstractPolyimide materials with high mechanical strength are widely used in various fields, but pose certain challenges in achieving sustainable material utilization. A poly(imide‐imide) vitrimer material (ADTA) based on multiple dynamic covalent bonds (imide, imine, and disulfide bonds) was constructed by preparing vanillin difunctionalized derivatives (DVA) for aldolamine condensation reactions with bis‐amine monomers (ATFA) and tris(2‐aminoethyl) amines (TAEA) with imide structures. The ADTA material has good 5% thermal stability Td5% (278.87°C), high energy storage modulus E (2421.26 MPa), and fast relaxation time (36.39 s). The thermal stability and mechanical properties of the material are enhanced by the more stable alicyclic structure of the imide structure. The material also demonstrated excellent solvent resistance and self‐healing properties. This study provides a new option for the development of sustainable utilization of polyimide materials.

Electrochemical characteristics of flexible open-cell supercapacitors employing different electrolyte types: KOH and ionic liquid

A carbonate hydroxide compound with substantial wettability was deposited on a porous Ni foam substrate, employing the Ni-based chemical precursor by a facile hydrothermal method. The resulting Ni2(CO3)(OH)2 electrode exhibits a nanowire structure characterized by a significant surface area. These electrodes represent highly promising materials for faradaic capacitors. They demonstrate high wettability on the electrode surface, facilitating charge and discharge processes on the electrode surface through redox reactions. A flexible hybrid open-cell supercapacitor, designed to operate at 1.5 V, was constructed with the Ni2(CO3)(OH)2 electrode as the positive terminal and graphene as the negative terminal, employing two distinct electrolytes (KOH and ionic liquid named MPPyFSI with 1-Methyl-1-propylpyrrolidinium Bis(fluorosulfonyl)imide structure). The open-cell devices, fabricated with 6 M KOH and MPPyFSI electrolyte, exhibit high energy densities of 39.6 and 24.8 Wh kg−1 and power densities of 1752.1 and 2908.5 W kg−1 at current densities of 2 A g−1, respectively. Furthermore, the energy storage devices utilizing aqueous KOH and MPPyFSI demonstrate excellent stability, maintaining 73.4 and 87.1% of their specific capacity after 5,000 charge/discharge cycles. The mechanical properties of the flexible open-cell device were characterized, and the electrochemical values corresponding to the banding angle of the device were measured.

Alloying synergistic flame retardant effect on PA6 by polyimide containing alkyl hypophosphate structure

A novel flame retardant − bismaleimide polyalkyl phosphinate aluminium (BPPA), containing both imide and phosphinate structures, was designed and synthesized to investigate the intramolecular synergistic flame retardant effect between imide and phosphinate structures and alloying effect of the imide structure with PA6. Based on the flame retardant and mechanical properties of BPPA/PA6 composites, the alloying flame retardant effect of BPPA on PA6 was systematically investigated. The PA6 material had almost no char after burning; however, BPPA can produce a large amount of residue and form a dense char layer during combustion of PA6 matrix, effectively reducing the heat release, while BPPA also improved the mechanical properties of PA6 composites through the alloying effect. The peak heat release rate (pk-HRR) decreased by 55.8 %, and the residue yield increased by 9.2 wt% for 20BPPA/PA6, compared with the PA6. After compounding aluminum diethylphosphinate (ADP) and BPPA, the flame retardancy of the composites can be further improved. The LOI value of the 8ADP/6BPPA/PA6 was increased to 29.8 % and passed the test of UL94 V-0 level. Its pk-HRR and residue yield were similar to that of the 14BPPA/PA6, which indicated that the compounding system of ADP and BPPA can provide excellent charring properties and gas-phase flame retardancy of PA6. Meanwhile, the alloying BPPA with PA6 not only reduced the effect on the tensile strength of ADP on PA6, but also improved the breaking elongation of the composite. In conclusion, it provides a new direction for developing high-performance halogen-free flame retardant polyamides.

Defect‐Repaired g‐C3N4 Nanosheets: Elevating the Efficacy of Sonodynamic Cancer Therapy Through Enhanced Charge Carrier Migration

AbstractSonodynamic therapy (SDT) has garnered growing interest owing to its high tissue penetration depth and minimal side effects. However, the lack of efficient sonosensitizers remains the primary limiting factor for the clinical application of this treatment method. Here, defect‐repaired graphene phase carbon nitride (g‐C3N4) nanosheets are prepared and utilized for enhanced SDT in anti‐tumor treatment. After defect engineering optimization, the bulk defects of g‐C3N4 are significantly reduced, resulting in higher crystallinity and exhibiting a polyheptazine imide (PHI) structure. Due to the more extended conjugated structure of PHI, facilitating faster charge transfer on the surface, it exhibits superior SDT performance for inducing apoptosis in tumor cells. This work focuses on introducing a novel carbon nitride nanomaterial as a sonosensitizer and a strategy for optimizing sonosensitizer performance by reducing bulk defects.

Defect-Repaired g-C3N4 Nanosheets: Elevating the Efficacy of Sonodynamic Cancer Therapy Through Enhanced Charge Carrier Migration.

Sonodynamic therapy (SDT) has garnered growing interest owing to its high tissue penetration depth and minimal side effects. However, the lack of efficient sonosensitizers remains the primary limiting factor for the clinical application of this treatment method. Here, defect-repaired graphene phase carbon nitride (g-C3N4) nanosheets are prepared and utilized for enhanced SDT in anti-tumor treatment. After defect engineering optimization, the bulk defects of g-C3N4 are significantly reduced, resulting in higher crystallinity and exhibiting a polyheptazine imide (PHI) structure. Due to the more extended conjugated structure of PHI, facilitating faster charge transfer on the surface, it exhibits superior SDT performance for inducing apoptosis in tumor cells. This work focuses on introducing a novel carbon nitride nanomaterial as a sonosensitizer and a strategy for optimizing sonosensitizer performance by reducing bulk defects.

Casting poly(urethane‐imide) elastomers with improved thermoviscoelasticity

AbstractPolyurethane (PU) is a versatile material that can be customized to meet specific commercial requirements in different industries because of its favorable mechanical properties. However, it is not resistant to high temperatures, and it requires structural modifications before it can be used in high‐temperature structural materials. In this study, isocyanates and anhydrides are copolymerized at high temperatures to obtain a solvent‐free oligomer, thus eliminating the risks associated with highly polar aprotic solvents. A casting technique is used to synthesize a solid poly(urethane‐imide) (PUI) elastomer. According to the results, casting PUI (CPUI) exhibits optimal physical properties at a hard segment content of 30.5%. Incorporating an ether, symmetric, or imide structure into CPUI may reduce its hysteresis and improve its thermal creep performance. Compared with PU, CPUI exhibits considerably higher creep aging resistance. In dynamic load application tests, CPUI wheels take a substantially longer time to reach failure compared with PU wheels. Overall, CPUI is an environmentally friendly material with high elasticity, low creep, and high heat aging resistance and is suitable for static and dynamic manufacturing applications.

Ultrastrong and High-Tough Thermoset Epoxy Resins from Hyperbranched Topological Structure and Subnanoscaled Free Volume.

The strength and toughness of thermoset epoxy resins are generally mutually exclusive, as are the high performance and rapid recyclability. Experimentally determined mechanical strength values are usually much lower than their theoretical values. The preparation of thermoset epoxy resins with high modulus, high toughness, ultrastrong strength, and highly efficient recyclability is still a challenge. Here, novel hyperbranched epoxy resins (Bn, n = 6, 12, 24)with imide structures by a thiol-ene click reaction. Bn shows an excellent comprehensive function in simultaneously improving the strength, modulus, toughness, low-temperature resistance, and degradability of diglycidyl ether of bisphenol-A (DGEBA). All the mechanical properties first increase and then decrease with minimization of the free volume properties. The improvement is attributable to uniform molecular holes or free volume by a molecular mixture of linear and hyperbranched topological structures. The precise measurement and controllability of the molecular free volume properties of epoxy resins is first discovered, as well as the imide structure degradation of crosslinked epoxy resins. The two conflicts are successfully resolved between strength and toughness and between high performance during service and high efficiency during degradation. These findings provide a route for designing ultrastrong, tough, and recyclable thermoset epoxy resins.

Long Cycle Life for Rechargeable Lithium Battery using Organic Small Molecule Dihydrodibenzo[c,h][2,6]naphthyridine-5,11-dione as a Cathode after Isoindigo Pigment Isomerization.

Sustainability and adaptability in structural design of the organic cathodes present promises for applications in alkali metal ion batteries. Nevertheless, a formidable challenge lies in their high solubility in organic electrolytes, particularly for small molecular materials, impeding cycling stability and high capacity. This study focuses on the design and synthesis of organic small molecules, the isomers of (E)-5,5'-difluoro-[3,3'-biindolinylidene]-2,2'-dione (EFID) and 3,9-difluoro-6,12-dihydrodibenzo [c, h][2,6]naphthyridine-5,11-dione (FBND). While EFID, characterized by a less π-conjugated structure, exhibits subpar cycling stability in lithium-ion batteries (LIBs), intriguingly, another isomer, FBND, demonstrates exceptional capacity and cycling stability in LIBs. FBND delivers a remarkable capacity of 175mAhg-1 at a current density of 0.05Ag-1 and maintains excellent cycling stability over 2000 cycles, retaining 90% of its initial capacity. Furthermore, an in-depth examination of redox reactions and storage mechanisms of FBND are conducted. The potential of FBND is also explored as an anode in lithium-ion batteries (LIBs) and as a cathode in sodium-ion batteries (SIBs). The FBND framework, featuring extended π-conjugated molecules with an imide structure compared to EFID, proves to be an excellent material template to develop advanced organic small molecular cathode materials for sustainable batteries.

Suppressing Defects‐Induced Non‐Radiative Recombination for Activating the Near‐Infrared Photoactivity of Red Polymeric Carbon Nitride

AbstractMany cases of light absorption modification exceeding 700 nm or near‐infrared (NIR) light are reported for capturing more than half of the solar energy, however, very few modifications can produce NIR photoactivity due to the inevitably introduced defects‐induced non‐radiative recombination. Here, taking four kinds of C/O co‐doped red polymeric carbon nitride as examples, defect‐repairing is carried out using alkali metal molten‐salts (LiCl/NaCl and LiCl/KCl) or solid‐salt (KCl) to activate their NIR photoactivity. The defect repair results from the passivation of alkali metal valence electron pairing and the formation of crystalline polyheptazine imide structure with more complete polymerization. More importantly, it sharply eliminates bulk defects (such as carbon vacancy and nitrogen vacancy) introduced by C/O co‐doping. Since structural defects are inevitably introduced in most photocatalysts during expanding light absorption, this proposed strategy is bound to be universal in suppressing defects‐induced non‐radiative recombination to activate NIR photoactivity.

Amphoteric dissolution of two-dimensional polytriazine imide carbon nitrides in water.

Crystalline two-dimensional carbon nitrides with polytriazine imide (PTI) structure are shown to act amphoterically, buffering both HCl and NaOH aqueous solutions, resulting in charged PTI layers that dissolve spontaneously in their aqueous media, particularly for the alkaline solutions. This provides a low energy, green route to their scalable solution processing. Protonation in acid is shown to occur at pyridinic nitrogens, stabilized by adjacent triazines, whereas deprotonation in base occurs primarily at basal plane NH bridges, although NH2 edge deprotonation is competitive. We conclude that mildly acidic or basic pHs are necessary to provide sufficient net charge on the nanosheets to promote dissolution, while avoiding high ion concentrations which screen the repulsion of like-charged PTI sheets in solution. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Design and synthesis of epoxy prepolymer containing aromatic imide structures for thermoset with excellent thermal, mechanical and dielectric properties

Recently, the development of epoxy thermosets with imide rings has received extensive attention due to their superior integrated properties, especially for thermal, mechanical and dielectric properties, compared to those of commercialized bisphenol A epoxy thermosets, yet remains substantial challenges, such as the high epoxy equivalent weight (EEW) of the epoxy prepolymers and the poor processibility of the epoxy systems. In this work, an imide-containing epoxy prepolymer (BAPT-EP) was facilely synthesized. It had a relatively low EEW of 340 g/equiv. and could be dissolved in hardener methylhexahydrophthalic anhydride (MHHPA) to give a homogeneous BAPT-EP/MHHPA system with good processibility. Thanks to the aromatic imide structures, the cured BAPT-EP/MHHPA showed improved overall properties. In particular, it had a 47.9 °C, 24.7 °C, 29.4%, 77.3% and 10.0% increase in the glass transition temperature, temperature at 5% mass loss, tensile strength, Young’s modulus and tensile toughness, respectively, compared to those of bisphenol A epoxy prepolymer (DGEBA)/MHHPA thermoset. Meanwhile, BAPT-EP/MHHPA thermoset featured good charring ability with a high char yield of 26.4% (800 °C/N2), remarkable dimensional stability with a low coefficient of thermal expansion of 52.5 ppm/°C and good dielectric properties with a low dielectric constant of 3.24 at 100 MHz. This work provides an elegant strategy to prepare high-performance epoxy thermosets with imide structures, which have promising applications in electronics.

Fluorinated polyimide with triphenyl pyridine structure for 5G communications: Low dielectric, highly hydrophobic, and highly transparent

With the rapid development of 5G communications, the traditional interlayer dielectric material polyimide (PI) requires modification due to its intrinsically high dielectric constant (Dk), high dielectric loss (Df), and high moisture absorption, which make it difficult to meet the needs of the high-frequency communications industry. In this paper, a new strategy for the preparation of novel PI with intrinsically low Dk and Df is proposed from the perspective of molecular structure design, the modification effect of superimposing bulky triphenyl pyridine structures and strong electronegativity groups, combined with long-chain anhydride to reduce the density of the imide structure. Therefore, three bulk diamine monomers (BPAB, PBAB3F, PBAB6F) containing triphenyl pyridine structures were designed in this paper and polymerized with 4,4′-(4,4′-isopropyldiphenoxy) phthalic anhydride (BPADA) to obtain three new PIs (PI-H, PI-CF3, PI-2CF3) with different fluorine contents, focusing on the relationship between structure and properties, especially the effect of fluorine content on dielectric properties. The results of the study show that the dielectric and hygroscopic properties of PI improve with increasing fluorine content. Among them, PI-2CF3 has the best overall performance, showing low dielectric (Dk = 2.72@10 GHz & Df = 0.00233@10 GHz), high transparency (Cut-off wavelength (λ0) = 389 nm, Maximum transmittance (Tvia) = 89%) and low hygroscopicity (Water absorption (Ma) = 0.246%, Contact angle (Ca) = 111°).

Synthesis and Properties of Polyamide 6 Random Copolymers Containing an Aromatic Imide Structure.

In order to adjust the properties of polyamide 6 (PA6) and expand its application, a new strategy of introducing an aromatic imide structure into the PA6 chain through the random copolymerization method is reported. The diimide diacid monomer was first synthesized by the dehydration and cyclization of pyromellitic dianhydride and 6-aminocaproic acid before it reacted with 1,6-hexamethylene diamine to form poly(amide imide) (PAI) salt, and finally synthesized PA6/PAI random copolymers containing an aromatic imide structure by the random copolymerization of ε-caprolactam and PAI salt. The introduction of an aromatic imide structural unit into the PA6 chain could have a great influence on its properties. As the content of PAI increases, the crystallinity (Xc) and melting temperature (Tm) of the PA6/PAI random copolymer gradually decrease, but its glass transition temperature (Tg) increases obviously. When the PAI content is 20 wt%, the copolymer PA6/PAI-20 has the best comprehensive performance and not only has high thermal stabilities but also excellent mechanical properties (high strength, high modulus, and good toughness) and dielectric properties (low dielectric constant and dielectric loss). Moreover, these properties are significantly superior to those of PA6. Such high-performance PA6 random copolymers can provide great promise for the wider applications of PA6 materials.

Solvent-Free Preparation of Thermally Stable Poly(urethane-imide) Elastomers

Polyurethanes (PUs) are widely used in many applications due to their versatile chemical and physical properties. To meet the increasing demands on PU with respect to intrinsic mechanical and thermal properties, they can be modified with thermally stable aromatic imide structures to form poly(urethane imide) (PUI). However, the preparation of PUI materials has been limited by the need for strong polar solvents, which hinder their industrial scale development. In this work, we prepared imide-containing isocyanate-terminated prepolymers via the reaction of polymeric aromatic or aliphatic isocyanates and pyromellitic dianhydride in completely solvent-free conditions. The subsequent PUI elastomers made from these prepolymers exhibited enhanced char formation and stiffness in comparison to the reference elastomers without imide structures, among which the aromatic PUI elastomer shows improved flame retardancy according to the initial cone calorimetry measurement. This work demonstrates the potential use of imide prepolymers in other PU applications where high thermal stability and flame retardancy are required. The solvent-free synthesis also paves a way for the large-scale production of PUI materials.

Cobalt Ferrite/Polyetherimide Composites as Thermally Stable Materials for Electromagnetic Interference Shielding Uses.

The progress of the automated industry has introduced many benefits in our daily life, but it also produces undesired electromagnetic interference (EMI) that distresses the end-users and functionality of electronic devices. This article develops new composites based on a polyetherimide (PEI) matrix and cobalt ferrite (CoFe2O4) nanofiller (10-50 wt%) by mixing inorganic phase in the poly(amic acid) solution, followed by film casting and controlled heating, to acquire the corresponding imide structure. The composites were designed to contain both electric and magnetic dipole sources by including highly polarizable groups (phenyls, ethers, -CN) in the PEI structure and by loading this matrix with magnetic nanoparticles, respectively. The films exhibited high thermal stability, having the temperature at which decomposition begins in the interval of 450-487 °C. Magnetic analyses indicated a saturation magnetization, coercitive force, and magnetic remanence of 27.9 emu g-1, 705 Oe, and 9.57 emu g-1, respectively, for the PEI/CoFe2O4 50 wt%. Electrical measurements evidenced an increase in the conductivity from 4.42 10-9 S/cm for the neat PEI to 1.70 10-8 S/cm for PEI/CoFe2O4 50 wt% at 1 MHz. The subglass γ- and β-relaxations, primary relaxation, and conductivity relaxation were also examined depending on the nanofiller content. These novel composites are investigated from the point of view of their EMI shielding properties, showing that they are capable of attenuating the electric and magnetic parts of electromagnetic waves.

Non-Thermal Ammonia Decomposition for Hydrogen Production over Carbon Films under Low-Temperature Plasma-In-Situ FTIR Studies.

Due to easy storage and transportation, liquid hydrogen carriers will play a significant role in diversifying the energy supply pathways by transporting hydrogen on a large scale. Thus, in this study, amorphous carbonaceous materials have been employed for hydrogen production via ammonia decomposition under non-thermal plasma (NTP) conditions. The adsorption and splitting of ammonia over carbons differing in the chemical structure of surface functional groups have been investigated by in situ spectral studies directly under NTP conditions. As a result of NH3 physical and chemical sorption, surface species in the form of ammonium salts, amide and imide structures decompose immediately after switching on the plasma environment, and new functionalities are formed. Carbon catalysts are very active for NH3 splitting. The determined selectivity to H2 is close to 100% on N-doped carbon material. The data obtained indicate that the tested materials possess excellent catalytic ability for economical, COx-free hydrogen production from NH3 at a low temperature.

Photodesign and fabrication of surface relief gratings on films of polyimide-based supramolecular systems obtained using host-guest strategy

New supramolecular structures were attained by an original approach based on mixing the concepts of polyamidic acid (PAA) host and an azochromophore guest with hydrogen bonding intermolecular interactions. The materials have been obtained and characterized for use as liquid crystal (LC) alignment layers. The azochromophore was introduced in the PAA solution in different ratio followed by casting on glass plate and thermal treatment to realize a film with imide structure, confirmed by Fourier-transform infrared spectroscopy (FTIR). Thermal analyses indicated that the dye loading in the polymer host slightly reduces the temperature of thermal decomposition from 508 to 466 °C, while glass transition temperature ranges between 244 and 213 °C. UV–Vis data proved that the samples exposure at the wavelengths of 355 nm is beneficial for surface relief gratings (SRGs) formation. Atomic force microscopy (AFM) evidenced the surface structuring of the samples and the changes in the spatial and functional contact area characteristics as a function of azo-dye amount. The attained grating periodicity was about 1 μm, while the depth ranged between 35 and 100 nm depending of the system composition. Surface anisotropy, bearing properties and fluid retention are enhanced upon chromophore incorporation. LCs anchoring energy increases with azochromophore percent up to 22.9 ∙ 10 −16 μJ/m 2 , which is desirable for LC display applications. • Supramolecular structures, based on a polymer matrix and an azo-dye, are achieved. • Transparent flexible polyimide films with heat resistance up to 466 °C are attained. • As the azo-dye loading increases LASER-made SRGs depth increases from 37 to 81 nm. • Anisotropy, bearing and fluid retention are enhanced upon azo-dye incorporation. • LC anchoring energy increases with azochromophore percent up to 22.9 ∙ 10 −16 μJ/m 2 .

New functionalisation reactions of graphitic carbon nitrides: Computational and experimental studies

The functionalisation of two-dimensional materials is key to modify their properties and facilitate assembly into functional devices. Here, new reactions have been proposed to modify crystalline two-dimensional carbon nitrides of polytriazine imide structure. Both amine alkylation and aryl-nitrene-based reactions have been explored computationally and with exploratory synthetic trials. The approach illustrates that alkylation is unfavourable, particularly at basal-plane sites. In contrast, while initial trial reactions were inconclusive, the radical-addition of nitrenes is shown to be energetically favourable, with a preference for functionalising sheet edges to minimise steric effects.

The effect of constructing discontinuous side chain D-A structure on high-performance poly (ether sulfone)s optoelectronic materials

The unconjugated high-performance polymers have been developing rapidly in the field of optoelectronics, due to the effective donor-acceptor (D-A) structure design strategy. Poly (ether sulfone) (PES) shows tremendous application potential in the field of optoelectronics by combining with optoelectronic units. Herein, an isolated D-A structure was constructed in the side chain of PES, in which the triphenylamine (TPA) structure was the donor and the imide structure was the acceptor. Electrochemical test showed that the onset potential of PES-TPAs was low (0.55 V). The PES-TPAs as a kind of electrochromic materials could improving their EC cycling stabilities from single-digit cycle times to 52 cycles (20% contrast reduction). To the best knowledge, no detail data was reported on the EC cycling stability of PES-type polymers before this work. Meanwhile, PES-TPAs as a kind of memory storage polymers exhibited a low threshold voltage (−3.03 V). These performances showed a wide application prospect of PES in the field of optoelectronics. More importantly, designing the molecular structure in this way would provide a new select for creating more types of optoelectronic polymers.

Enhanced reactive-oxygen-species generation and photocatalytic efficiency with internal imide structures of different ratio in metal-free perylene-g-C3N4 semiconductors

A metal-free and straightforward protocol for the photocatalytic synthesis of phenols from arylboronic acids has been demonstrated using perylene-tri-s-triazine (perylene-g-C3N4) polymeric semiconductors. Tri-s-triazine and perylene are connected through imide bonds to give catalysts P−M of high imide-bond ratio and P+M of low imide-bond ratio. The aerobic hydroxylation of arylboronic acids can be operated at room temperature and atmospheric environment under white-light LED irradiation. This research work has revealed that internal imide functional groups within the catalyst’s molecular structures can facilitate the ROS (O2−, OH and 1O2) generation and O2− is the decisive specie in the hydroxylation due to the faster reaction rate compared with OH and 1O2, with yield as high as 97%. This environment-friendly method and the molecule design principle will provide a valuable strategy for developing metal-free polymeric semiconductors with specific molecular structures and deep insights into the ROS− involved catalysis in photo-generated chemical transformations.