Polyimide Oligomers Research Articles

Enhancing the interlaminar property of carbon fiber/poly(aryl ether ketone) composites with water‐soluble polyimide oligomer sizing agent

AbstractNovel water‐soluble polymer‐based sizing agents for carbon fiber/poly(aryl ether ketone) composites (CF/PAEK) have gained attention. However, a challenge remains: the sized CF bundles lack flexibility, and the effect of this on the properties of the composite has not been discussed. Herein, a water‐soluble polyimide oligomer (OL) sizing agent was developed, and the sizing effect was comprehensively evaluated. The conventional molecular weight polyimide (HP) sizing agent was also assessed for comparison. Although the interfacial shear strength of the sized CF monofilaments is enhanced due to improved surface roughness and wettability, the effect of the OL sizing agent on the composite's interlaminar shear strength (ILSS) and tow's flexibility differed from that of the HP sizing agent. Compared with HP‐CF, the yarn spreading rate of OL‐CF tow is increased by about eight times, and the ILSS of OL‐CF/PAEK composites with 2 and 5 MPa molding pressure is increased by 69% and 222%, respectively. The HP sizing agent weakens the tow's flexibility and yarn spreading ability, which is not conducive to the resin penetration in the tow, resulting in lower ILSS. In contrast, the OL sizing agent considers the tow's flexibility and composite's interlaminar property, showing great application potential.Highlights Two PI‐based sizing agents with diverse film‐forming capacities were prepared. The ILSS of CF/PAEK with OL sizing agent was significantly improved. HP sizing agent weakened the tow flexibility and interlaminar property. The interaction of sizing layer—resin penetration—ILSS was proposed.

Toward MOF@Polymer Core-Shell Particles: Design Principles and Potential Applications.

ConspectusCompositing MOFs with polymers brings out the best properties of both worlds. The solubility and excellent mechanical properties of polymers endow the brittle, powdery MOFs with enhanced processability, thereby enriching their functions as solid sorbents, filters, membranes, catalysts, drug delivery vehicles, and so forth. While most MOF-polymer composites are random mixtures of two materials with little control over their fine structures, MOF@polymer core-shell particles have recently emerged as a new platform for precise composite design. The well-defined polymer coating can keep the rich pore characteristics of the MOF intact while furnishing the MOF with new properties such as improved dispersibility in various media, tunable surface energy, enhanced chemical stability, and regulated guest diffusion. Nevertheless, the structural and chemical complexity of MOFs poses a grand challenge to the development of a generalizable and feasible strategy for constructing MOF@polymer. Examples in the literature that showcase the presence of a well-defined polymer shell on the MOF with fully reserved porosity are rare. Moreover, methods for coating MOFs with condensation polymers (e.g., polyimide, polysulfone) are severely underexplored, despite their clear potential as membrane materials. In this Account, we present our group's effort over the past 4 years on the synthesis and applications of MOF@polymer composites. We first described a highly generalizable surface polymerization method that utilizes the rapid physisorption of a random copolymer (RCP) to carry initiating groups to the MOF surfaces. Subsequent controlled radical polymerization led to the formation of a uniform methacrylate or styrenic polymer on the MOF with tunable thickness and composition. To utilize the properties of condensation polymers, we pioneered the covalent grafting of polyimide (PI) brushes to UiO-66-NH2 surfaces. In addition, to circumvent the need for a covalent anchoring group, we further developed an MOF surface grafting method based on mechanical linkage. Instead of connecting to the ligand, polyimide (PI) oligomer was linked to a functionalized linear polymer physically entangled within an MOF, thus realizing surface grafting with PI. Alternatively, PIs, polysulfone (PSF), and polycarbonate (PC) can also be grafted to various MOF surfaces through a metal-organic nanocapsule (MONC)-mediated method using a combination of electrostatic interaction and coordination bonds. To find a rapid and low-cost surface coating method suitable for commercialization, a new approach called non-solvent-induced surface-aimed deposition (NISAP) was developed. The action of the solvent phase separation drives dianhydrides and polyamines to the MOF surface, thus realizing accelerated polymerization and the rapid formation of a polymer coating on the MOF. Finally, we provided an overview of the unique properties and potential applications of MOF@polymer composites, including improved stability, MMMs, porous liquids (PLs), and immobilizing homogeneous catalysts. We hope that this Account can inspire more researchers to further develop and optimize the synthetic strategies for MOF@polymer and uncover its full application potential.

A Physical Entangling Strategy for Simultaneous Interior and Exterior Modification of Metal–Organic Framework with Polymers

AbstractA new strategy uses a common feature of metal–organic frameworks (MOFs), namely porosity rather than functionality, to achieve simultaneous interior and exterior modification of a MOF with polymers. We demonstrate that an anhydride‐terminated polyimide oligomer can be covalently grafted to the amine‐functionalized methacrylate polymer backbone residing underneath the MOF surface and physically entangled within the 3D nanochannels. The MOF particles were evenly coated with a thin layer of polyimide brushes on the surface thereby exhibiting increased dispersibility in solvent media as well as in polymer matrix. The MOF pores were decorated with aliphatic amine groups to endow the MOF with higher CO2 affinity at low pressure. The polyimide‐grafted surface allowed MOF particles to interact favorably with the polyimide matrix, producing defect‐free MMM with drastically improved CO2 permeability and maintaining the inherent CO2/N2 and CO2/CH4 selectivity of the neat polymeric membrane.

A Physical Entangling Strategy for Simultaneous Interior and Exterior Modification of Metal-Organic Framework with Polymers.

A new strategy uses a common feature of metal-organic frameworks (MOFs), namely porosity rather than functionality, to achieve simultaneous interior and exterior modification of a MOF with polymers. We demonstrate that an anhydride-terminated polyimide oligomer can be covalently grafted to the amine-functionalized methacrylate polymer backbone residing underneath the MOF surface and physically entangled within the 3D nanochannels. The MOF particles were evenly coated with a thin layer of polyimide brushes on the surface thereby exhibiting increased dispersibility in solvent media as well as in polymer matrix. The MOF pores were decorated with aliphatic amine groups to endow the MOF with higher CO2 affinity at low pressure. The polyimide-grafted surface allowed MOF particles to interact favorably with the polyimide matrix, producing defect-free MMM with drastically improved CO2 permeability and maintaining the inherent CO2 /N2 and CO2 /CH4 selectivity of the neat polymeric membrane.

Structure and dynamics of small polyimide oligomers with silicon as a function of aging.

The effect of UV curing and shearing on the structure and behavior of a polyimide (PI) binder as it disperses silicon particles in a battery electrode slurry was investigated. PI dispersant effectiveness increases with UV curing time, which controls the overall binder molecular weight. The shear force during electrode casting causes higher molecular weight PI to agglomerate, resulting in battery anodes with poorly dispersed Si particles that do not cycle well. It is hypothesized that when PI binder is added above a critical amount, it conformally coats the silicon particles and greatly impedes Li ion transport. There is an "interzonal region" for binder loading where it disperses silicon well and provides a coverage that facilitates Li transport through the anode material and into the silicon particles. These results have implications in ensuring reproducible electrode manufacturing and increasing cell performance by optimizing the PI structure and coordination with the silicon precursor.

Development of High-Performance Composites with Molecular Weight Controlled Polyimide Oligomers End-Capped with Phenylethynyl Groups

A series of molecular weight controlled polyimide oligomer (Oligo-PI) resins were developed via the polymerization of 4,4′-(1,3-phenylenedioxy)dianiline (TPE-R), 2,3′,3,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4-phenylethynyl phthalic anhydride (PEPA). PEPA was served as the molecular weight controlling and reactive end-capping agent. Oligo-PI resins have an asymmetric and amorphous structure, which could make better processability to fabricate composites. To investigate the effect of molecular weight (MW) and chain extension structures of phenylethynyl groups by thermal curing on thermal and mechanical properties, carbon fabric reinforced Oligo-PIs (Oligo-PI/CFs) were prepared via hot press technique. Morphology, mechanical and thermal properties of Oligo-PI/CFs were measured by SEM, TGA, IZOD impact tester, and UTM (three-point bending test). As MW got higher and the ordered network structures were formed, the composite exhibited excellent thermal stability. Flexural strengths also increased by building the crosslinked structures. On the other hand, impact strengths were less influenced. Among Oligo-PI/CFs, Oligo-PI/CF-3 showed comparatively good performance. The mechanical properties of Oligo-PI/CF-3 (5 ply) was evaluated at both 25 °C and 200 °C. The composite maintained high strengths even at high temperatures, demonstrating the durability of Oligo-PI/CFs in harsh conditions utilized for the aerospace and military applications.

Performance of high-temperature thermosetting polyimide composites modified with thermoplastic polyimide

The preparation of polyimide (PI) resin with high heat resistance and toughness is a significant challenge. In this study, thermoplastic PI (TPI) was used to toughen thermosetting PIs, and toughened PI (TPI/PI) blends were prepared. The modified PI resin system exhibited good thermal stability, excellent heat resistance, and high toughness. The results indicated that the TPI/PI blends maintained the curing behavior and characteristics of the PI oligomer. The Tg of the cured TPI/PI blend exceeded 395 °C, and the T5% values were in the range of 533–563 °C, suggesting excellent thermal stability and heat resistance. The maximum impact strength was increased by 46% compared with that of pure PI, indicating the excellent toughening effect of the TPI. Carbon fiber-reinforced PI composites were prepared using the toughening system as a matrix. The compression-after-impact values of the carbon fiber-reinforced PI composites were up to 190 MPa, indicating the excellent toughness of the materials.

The effect of methyl and methoxy substituents on dianilines for a thermosetting polyimide system

4,4′-Methylenedianiline (MDA) is widely used in high-temperature polyimide resins, including polymerization of monomer reactants-15. The toxicity of MDA significantly limits the manufacturability using this resin. Modifying the substitution and electronics of MDA could allow for the reduction of toxicity while maintaining the high-performing properties of the materials derived from the modified MDA. The addition of a single methyl substituent, methoxy substituent, location of these substituents, and location of the amine relative to the phenolic bridge were modified as were other non-aniline diamines. Various anilines were condensed with paraformaldehyde under acidic conditions to yield dianilines. These dianilines and diamines were reacted with nadic anhydride and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride in methanol to form the polyamic acid oligomers and heated at elevated temperature to form polyimide oligomers. It was found that the molecular weight of the oligomers derived from MDA alternatives was generally lower than that of MDA oligomers resulting in lower glass transition temperatures ( T gs) and degradation temperatures. Additionally, methoxy substituents further reduce the T g of the polymers versus methyl substituents and reduce the thermal stability of the resin. Methyl-substituted alternatives produced polyimides with similar T gs and degradation temperatures. The toxicity of the MDA alternatives was examined. Although a few were identified with reduced toxicities, the alternatives with properties similar to that of MDA also had high toxicities.

Toward Improved Optical Transparency of Polyimide Aerogels.

Highly translucent polyimide aerogels were prepared by combining equimolar amounts of pyromellitic dianhydride, 4,4'-hexafluoroisopropylidene di(phthalic anhydride) (6FDA), and 2,2'-dimethylbenzidine and cross-linking with 1,3,5-benzenetricarbonyl trichloride. A multivariable statistical design of experiments was used to perform a comparison study between three variables used to fabricate the aerogels: formulated repeat unit (n) of polyimide oligomers, 6FDA fraction of total dianhydride (0-50 mol %), and total polymer concentration in solution (7-10 wt %). Polymers with 25 mol % 6FDA in the backbone structure were found to produce polyimide aerogels with high optical transmission and low haze. These aerogels also possessed higher surface areas and very narrow nanoscale pore size distribution. Because of the decreased thermal conductivity with increasing amount of 6FDA in the backbone, these aerogels may find use where the combination of high optical transparency and thermal impedance is desired, such as insulated window panes. To this end, future efforts will focus on reducing the yellow color of the polyimide aerogels.

Preparation of low-κ polyimide resin with outstanding stability of dielectric properties versus temperature by adding a reactive Cardo-containing diluent

High stability of low-κ value in a broad temperature region is a critical property for low dielectric constant polymer materials especially when they are served in some harsh conditions. However, most polymer dielectrics always exhibit a significant variation in dielectric property at around Tg or sub-Tg due to the local segment or chains motion, thus, low-κ polymer dielectrics are limited to a relatively narrow working temperature region. Herein, we described a series of novel crosslinked polyimide (PI) thermosets by blending a reactive Cardo-containing diluent into the PI oligomer, the dielectric constants of which were greatly reduced from 3.4 to 2.5 and were surprisingly stable over a temperature region of -150-250 °C. Meanwhile, the cured blended thermosets exhibited a 32–139 °C increase in Tg compared to the pristine PI. Detailed analyses have illustrated that the significantly reduced κ value, highly stable dielectric property and superior stability of these blended samples are originated from the synergistic effects of the large free-volume of Cardo-containing diluent, looser molecule packing resulted from the TR reaction and the highly crosslinked network. This desirable combination of facile processability, attractive dielectric behavior and excellent thermal stability makes them potential utilization in aerospace, microelectronic industries and other harsh environment applications.

Preparation and wear resistance properties of thermosetting polyimide composites containing solid lubricant fillers

A polyimide (PI) oligomer end-capping with 4-phenylethynyl anhydride was successfully synthesized to prepare a series of thermosetting PI composites containing solid lubricant fillers MoS2, SiO2, Si3N4, or graphite via hot-press-molding technique. Friction and wear tests were carried out under dry friction condition and the effects of friction and wear properties of PI containing difference solid fillers were also investigated. The results indicated that the type and content of the incorporation fillers played an important role in the wear resistance properties of PI composites. Among the prepared composites, PI/MoS2-20 wt% composites showed the lowest friction coefficient (0.11), which was decreased by 47.6% compared to pure PI. While PI/graphite-20 wt% composites showed the least wear loss of 0.864 mg, which was a 90.4% decrease compared to pure PI. Furthermore, the tensile strength of PI/graphite-20 wt% composites showed an increase of 18.7% compared to pure PI. Moreover, the thermal stability and thermal conductivity of PI was improved with the incorporation fillers. The wear type of worn surfaces gradually changed from adhesion wear and fatigue wear of pure PI into abrasive wear of PI composites. The resultant PI composites exhibited good wear resistance, mechanical, thermal conductivity and thermal stability properties, suggesting their potential applications as high-performance friction materials.

Utilizing Polyhexahydrotriazine (PHT) to Cross-Link Polyimide Oligomers for High-Temperature Shape Memory Polymer

Integrating good strength and toughness, high thermostability, and easy processability into one shape memory polymers is highly desirable yet challenging. Herein, we demonstrate an approach to fabr...

Phenylethynyl-terminated oligoimides with ultra-low melt viscosity derived from 1,4-bis(3,4-dicarboxy phenoxy)benzene dianhydride

Most of the existing polyimide oligomers for resin transfer molding (RTM) processing exhibited high melt viscosity, which can only maintain below 1 Pa·s at 280°C for 2 h, leading to very high process temperatures. So novel RTM-type oligomers with lower and stable melt viscosities are more desirable. Three series of thermoset oligoimides derived from 1,4-bis(3,4-dicarboxy phenoxy)benzene dianhydride and three different aromatic diamines were prepared herein. The diamines included 4,4′-oxydianiline, 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 2-phenyl-4,4′-diaminodiphenyl ether ( p-ODA). 4-Phenylethynylphthalic anhydride was used as an endcapping reagent. Effects of the chemical structures and molecular weights of the oligoimides on their aggregated structures, melt processability, and the thermal and mechanical properties of the cured films were then systematically investigated. X-Ray diffraction results indicated that ODA series oligoimides and TFDB series oligoimides showed crystallinity in various degrees. However, the asymmetric p-ODA enables the p-ODA series oligoimides to exhibit amorphous forms. It was found that the p-ODA-based oligoimide with a molecular weight of 750 g mol−1 showed very low melt viscosity of 1 Pa·s even at 210°C, and the melt viscosity could maintain below 1 Pa·s after isothermal aging for 2 h at any temperature in the range of 200–280°C by rheological measurements. The cured film also showed a high glass transition temperature of 355°C by dynamic mechanical analysis, very good thermal stability by thermogravimetric analysis, and good mechanical properties. It might be more suitable for RTM processes in the future.

Novel high-performance poly(benzoxazole-co-imide) resins with low dielectric constants and superior thermal stabilities derived from thermal rearrangement of ortho-hydroxy polyimide oligomers

Unsatisfied dielectric property and insufficient thermal stability are major obstacles for the commercialization of polyimide resins in the future ultralarge scale integration (ULSI) or radar-wave-transparent composite applications. The incorporation of ortho-hydroxy diamine into a common phenylethynyl terminated oligoimides, aiming to subsequently form additional rigid benzoxazole units by the thermal rearrangement (TR), were prepared. The effects of TR-able codiamine on the processing ability of oligoimides, molecular packing and properties, including thermal stability, dielectric property and bonding ability to reinforcing fibers, for the resulting poly(imide-co-benzoxazole) (PI-co-PBOs) resins have been examined in detail. These thermally rearranged PI-co-PBO resins exhibit reduced dielectric constants of 2.56–3.4 at f = 0.1 GHz, lower than the cured PI with a dielectric constant of 3.55. Meanwhile, the 5 wt% weight loss temperature (Td5) of the resultant resins increases from 455 °C for the cured PI to 491 °C for the PI-co-PBO-60 containing 60 mol% benzoxazole unit, and correspondingly, the tensile modulus of PI-co-PBO-60 reaches 2.47 GPa, which is 76% higher than that of the cured PI. These resultant PI-co-PBOs exhibit the combined excellent properties, indicating them a great potentials as the new low-dielectric constant polymer resins in microelectronic industries or advanced composites.

Synthesis of Polyimides in Molecular-Scale Confinement for Low-Density Hybrid Nanocomposites.

In this work, we exploit a confinement-induced molecular synthesis and a resulting bridging mechanism to create confined polyimide thermoset nanocomposites that couple molecular confinement-enhanced toughening with an unprecedented combination of high-temperature properties at low density. We describe a synthesis strategy that involves the infiltration of individual polymer chains through a nanoscale porous network while simultaneous imidization reactions increase the molecular backbone stiffness. In the extreme limit where the confinement length scale is much smaller than the polymer's molecular size, confinement-induced molecular mechanisms give rise to exceptional mechanical properties. We find that polyimide oligomers can undergo cross-linking reactions even in such molecular-scale confinement, increasing the molecular weight of the organic phase and toughening the nanocomposite through a confinement-induced energy dissipation mechanism. This work demonstrates that the confinement-induced molecular bridging mechanism can be extended to thermoset polymers with multifunctional properties, such as excellent thermo-oxidative stability and high service temperatures (>350 °C).

Polyimide Aerogels Using Triisocyanate as Cross-linker.

A family of polyimide (PI)-based aerogels is produced using Desmodur N3300A, an inexpensive triisocyanate, as the cross-linker. The aerogels are prepared by cross-linking amine end-capped polyimide oligomers with the triisocyanate. The polyimide oligomers are formulated using 2,2'-dimethylbenzidine, 4,4'-oxydianiline, or mixtures of both diamines, combined with 3,3',4,4'-biphenyltetracarboxylic dianhydride, and are chemically imidized at room temperature. Depending on the backbone chemistry, chain length, and polymer concentration, density of the aerogels ranged from 0.06 to 0.14 g/cm3 and Brunauer-Emmett-Teller surface areas ranged from 350 to 600 m2/g. Compressive moduli of these aerogels were as high as 225 MPa, which are comparable to, or higher than, those previously reported prepared with similar backbone structures but with other cross-linkers. Because of their lower cost and commercial availability as cross-linker, the aerogels may have further potential as insulation for building and construction, clothing, sporting goods, and automotive applications, although lower-temperature stability may limit their use in some aerospace applications.

Synthesis and characterization of a high temperature thermosetting polyimide oligomer derived from a non-toxic, sustainable bisaniline

A high temperature, hydrophobic thermosetting polyimide oligomer has been prepared from a non-toxic, bio-based bisaniline derived from p-cymene.

Negative-tone Photodefinable Underfill Having High Resolution and Appropriate Thermal Fluidity

Photodefinable wafer level underfill (PWLUF) has been evaluated for chip to substrate stacking. The good fluidity of PWLUF after patterning is required for chip and substrate stacking. PWLUF was designed using polyimide, acrylates, epoxides and some additives. It was difficult to improve the fluidity of patterned PWLUF keeping resolution by changing the composition ratio of acrylates and epoxides. On the other hand, PWLUF using the polyimide oligomer obtained by increasing end capping agent ratio improved the fluidity as well as the resolution. The chip to substrate stacks afford void-free bump soldering without underfill entrapment. We also successfully demonstrated the reflow soldering process using PWLUF.

Phenylethynyl-Terminated Polyimide Oligomers with Low Viscosity and Good Thermal Properties

A series of addition-type imide oligomer (degree of polymerization: n=1-9) derived from 2,3,3',4'-diphenyl ether tetracarboxylic acid dianhydride (a-ODPA), 3,4'-oxydianiline (3,4'-ODA) and 4-phenylethynylphthalic anhydride (PEPA) was synthesized by thermal imidization. The resultant oligomers were characterized for their chemical architecture, thermal property, and processability. The experimental results showed that oligomers PI-1 and PI-2 had somewhat crystalline phase. PI-4, PI-6 and PI-9 exihibited high solubility in solvents. These imide oligomers have a very low melt viscosity, and thus provide wide processing window by the rheological behaviors. Furthermore, the cured polyimides exhibited excellent thermal stability under N2 atmosphere. The temperatures of 5% weight loss in N2 atmosphere were all above 524°C.

Poly(maleic anhydride) cross-linked polyimide aerogels: synthesis and properties

A series of aerogels was fabricated by cross-linking amine end-capped polyimide oligomers with poly(maleic anhydride)s.