Phthalonitrile Resins Research Articles

Convenient synthesis of phthalonitrile‐containing mono‐benzoxazines with exceptional thermal stability and improved curing activity

AbstractSimple synthesis and high performance are eternal pursuit for polymers. To lower the curing temperature, lower the melt viscosity and improve the processability of high performance phthalonitrile resins, a solvent‐free method was applied to synthesize three from different phenols. Their chemical structure was confirmed by FTIR and NMR spectra, the curing behavior was investigated by DSC and rheology. It was found that the polymerization of phthalonitrile groups could be effectively promoted by benzoxazine moieties and the curing temperature of phthalonitrile groups dropped to around 240°C. Consequently, owing to the high curing reactivity, polymers obtained at relatively low curing temperature possessed high crosslinking density and extremely high thermal stability. P‐apn‐200, which was cured at 200°C, showed 5 wt% weightloss temperature (Td5) of 472°C and char yield (Yc) of 75.77% at 800°C. Moreover, the polymers obtained after curing at 280°C showed superior dimensional stability, CN‐apn‐280 showed extremely low linear expansion coefficient (CTE) of 10.7 ppm/°C. And mP‐apn‐280 showed HR capacity of 3.99 J/g‧K, peak HRR of 4.0 W/K and total HR of 0.8 kJ/g.

Effect of curing behaviors on performances of phthalonitrile resins: A deep molecular dynamics exploration with experiment

The curing process and mechanism of high-performance phthalonitrile (PN) thermosetting resin are crucial for its excellent mechanical and thermal-oxidation properties. The complicated polymerization reactions of PN resins were effectively controlled to obtain three types of major cured products (triazine, polyindoline and phthalocyanine). The corresponding cross-linking evolution processes and atomistic microstructural models were dynamically constructed and visualized through a creatively self-compiled procedure. Molecular dynamics simulations combined with experiment were properly conducted on two typical PN resins to illustrate the relationship between cross-linked microstructures and performance. The cross-linking degree and types of final products are positively correlated with the mechanical strength of PN resin. The hydrogen bonds present in the cross-linked structure mainly consolidate the cured networks of PN resin and the unique phenolic hydroxyl groups in PN75 enhance the hydrogen bonding contribution. The dominant pyrolysis gases were experimentally detected and distinguished as H2O, NH3, HCN, CH4, CO2 and CO during the thermal pyrolysis process of PN resin as the temperature rose. This work provides a new approach to probe the curing process and generated species, and further tailor the mechanical behavior and thermal-oxidation properties of resins or composites.

A novel approach to simultaneously modulate the processability and thermal performance of phthalonitrile resin through the strategic use of thioether bonds

Phthalonitrile (PN) resin is renowned for its absence of small molecule release during curing, high processing stability, and exceptional thermal stability, positioning it favorably in the realm of high-temperature resin applications. However, its narrow processing window and high melting point present challenges to its development and practical use. To address these limitations, this work synthesized PN prepolymers 4,4′-bis (sulfonylbiphenyl) thiophtalonitrile (BSPS) and 4,4′-bis(carbonylbiphenyl) thiophtalonitrile (BSPC) by introducing thioether bonds as a substitute for ether bonds, aiming to expand the prepolymers' processing window. Meanwhile, building upon the oxidation process of thioether to sulfone observed in pharmaceutical production, the potential for in-situ oxidation of thioether bonds during the curing of phthalonitrile prepolymers was investigated. A comprehensive analysis of the curing behavior, viscosity changes, and thermal stability was conducted using differential scanning calorimetry (DSC), rheological analysis, and thermogravimetric analysis (TGA). The DSC and rheological test results reveal that the experimental group prepolymers BSPS and BSPC exhibit lower melting points (BSPS 179 °C; BSPC 180 °C) and broader processing windows (BSPS 52 °C; BSPC 79 °C) than blank. Additionally, the thermal performance of resins show improvement over the blank, with BSPS achieving a decomposition temperature of up to 530 °C (Td5%). XPS analysis of the curing process confirmed that the enhanced thermal stability is attributable to the partial oxidation of thioether bonds into stable sulfone groups. This innovative structural approach allows for satisfactory processing performance in the initial stage, followed by a spontaneous transformation into a more robust and thermo-resistant structure post-shaping. This finding carries significant implications for the development of a balanced phthalonitrile system that harmonizes processing ease with superior thermal endurance.

Improving the curing reactivity, interfacial strength, thermal and mechanical properties of phthalonitrile resin/basalt fiber composites by reactive organic coating

Phthalonitrile (PN) resin is a thermosetting resin with excellent properties, but its poor processability hinders its wide application. Meanwhile, as a high-performance green fiber, basalt fiber (BF) shows good overall properties, but the chemical inertness and smooth surface limits its application as well. In this work, a highly reactive organic coating polydopamine (PDA) was used to promote the curing of PN resin and enhance the interfacial interaction between the polymer matrix and the fiber cloth. The successful coating of PDA was verified by SEM observation, FTIR and XPS spectra. It was found that PDA could not only increase the polarity of BF, aid the infiltration of PN resin into the fiber cloth, enhance the interfacial strength, but also promote the consumption of cyano groups and increase the chemical crosslinking density. Consequently, the overall performance of the composites was enhanced. Specifically, the laminate 0.4DABF/BAPh showed flexural strength of 447 MPa and flexural modulus of 23.3 GPa, which was 131 MPa and 4.5 GPa higher than those of BF/BAPh. The glass transition temperature of 0.4DABF/BAPh was also 77 °C higher than that of BF/BAPh.

Copolymerization of novel self-promoted curing phthalonitrile with epoxy resin and its thermal property

The disadvantage of poor thermal performance of epoxy resin limits its application in special fields, therefore we improve the thermal performance of epoxy resin by copolymerizing it with phthalonitrile resin. A novel self-promoted curing phthalonitrile monomer containing pyridine rings and amino groups (APNH) was successfully synthesized using 2-amino-4-hydroxypyridine and 4-nitrophthalonitril, and characterized by FTIR and NMR spectra. DSC confirmed that the APNH monomer exhibits curing behavior that is self-promoting. Copolymerizing the APNH monomer with epoxy resin enhances the thermal performance of the epoxy resin. The curing behavior of the EPNH copolymer was studied using DSC, which revealed two distinct curing peaks. FTIR analysis showed that the EPNH copolymer has formed structures such as triazine, phthalocyanine, and isoindoline. The presence of cyano groups significantly enhances the thermal properties of the copolymer, surpassing those of traditional epoxy resins. This enhancement in thermal performance amplifies with an increase in the content of the APNH monomer. The research indicates that the EPNH copolymer exhibits superior thermal stability and elevated glass transition temperatures, facilitating the application of epoxy resin in specialized areas.

Recent Advances and Prospects in High‐Performance Bio‐Based Phthalonitrile Resins

AbstractPhthalontirile resins are renowned as the most heat‐resistant polymeric materials and exhibit exceptional performance under harsh conditions. Consequently, phthalonitrile thermosets offer the potential to substitute metals in hot parts, thereby broadening the operational limits of plastic materials in high‐tech applications. Given their unique combination of properties, phthalonitriles have garnered significant demand across sectors such as aerospace, automotive, electronics, and renewable energy. With industrial production and application of phthalonitriles recently initiated in several countries, questions regarding the sustainability of these materials have naturally arisen. Thermosetting materials, owing to their highly cross‐linked architecture, cannot be recycled, necessitating the adoption of synthetic methods utilizing bio‐feedstock raw materials and green protocols to mitigate their environmental impact. The present prospective review summarizes and analyzes the current state‐of‐the‐art in bio‐based phthalonitrile resins and discusses potential directions for research and development of new application areas, with a focus on the challenge of maintaining high‐performance levels during the transition to bio‐based raw materials.

Effect of Phosphate-Bridged Monomer on Thermal Oxidative Behavior of Phthalonitrile Thermosets.

Phthalonitrile thermosets are known for their excellent mechanical, physico-chemical, and fire-retardant properties, making them attractive for aerospace and mechanical engineering applications. When producing and applying phthalonitrile-based structural parts, it is essential to consider aspects such as processability and the long-term stability of the material's properties at high temperatures. In our previous studies, we demonstrated that resins containing phosphate-bridged bisphthalonitrile monomers are easily processable due to their low melting temperature and wide processing window. In this study, we investigated the impact of bis(3-(3,4-dicyanophenoxy)phenyl)phenyl phosphate (PPhPN) monomer content on physico-chemical and mechanical properties, thermal stability, and thermal oxidative stability. This research highlights the importance of conducting long-term thermal oxidative aging studies in addition to thermogravimetric analysis to properly assess the stability of thermosets. The findings indicate that adding less than 15% of PPhPN results in the formation of a crystalline phase, which impairs the resin's processability. Conversely, a high PPhPN content reduces the material's thermal oxidative stability. Therefore, based on mechanical and physico-chemical tests after thermal oxidative aging, it can be concluded that a 10-15% concentration of the phosphate-containing monomer enables easy processability of the phthalonitrile resin and provides excellent long-term thermal oxidative stability at temperatures up to 300 °C, while maintaining a flexural strength exceeding 120 MPa and an elasticity modulus of 4.3 GPa.

High-temperature wave-transparent and intrinsically flame-retardant phthalonitrile/quartz composite based on a straightforward hot-melt prepreg process

Wave-transparent composite materials are becoming increasingly critical for advancing robust human-machine interaction systems. A pivotal component of these systems is an organic resin matrix, which is currently the focus of intensive research. Herein, to develop a phthalonitrile resin capable of withstanding temperatures exceeding 500 °C, two types of Si/P-containing alkynyl curing agents (Si-ALK and P-ALK) were synthesized and integrated with sulfur-enriched phthalonitrile monomers (SSS-PN) to fabricate an organic-inorganic hybrid phthalonitrile（PN）resin. The resulting hybrid resin demonstrated exceptional thermal stability (594 °C for 10 % Si-PN-450 °C; 626 °C for 50 % P-PN-450 °C) and thermal oxygen stability (569 °C for 10 % Si-PN-450 °C; 594 °C for 30 % P-PN-450 °C). The Si-ALK/P-ALK and SSS-PN blends maintained stable low-viscosity properties for an extended period of up to 180 min, which is advantageous for the facile production of quartz fiber-infused composites (Si-PN/QF and P-PN/QF) through a straightforward and eco-friendly melt processing approach. The cured PN composite (30 % Si-PN-450 °C/QF vs. 10 % P-PN-450 °C/QF) exhibited significantly improved glass transition temperatures (506 °C vs. 553 °C), acceptable flexural strength (268 MPa vs. 275 MPa), and excellent flame retardancy (less than 8.0 % weight loss exposed at 1300 °C for 200 s). Additionally, the composites demonstrated commendable dielectric properties, with a dielectric constant (Dk) of approximately 4.0 and a dissipation factor (Df) below 0.01 from 25 °C to 600 °C. Collectively, the obtained composites exhibited a synergistic combination of thermal, fire-resistant, and dielectric properties, positioning them as leading candidates for the next generation of wave-transparent materials.

Vanillin based phthalonitrile and acetylene bifunctional resins

AbstractThe renewable and biosynthetic molecule, vanillin, were used in the preparation of new phthalonitrile (PN) and ethynylbenzene (EB) bifunctional resins without pre‐modification of the vanillin structure. This PN resin was characterized by differential scanning calorimetry, thermogravimetric analysis, nuclear magnetic resonance spectroscopy, rheometry, and single crystal x‐ray diffraction. The monomers exhibited excellent rheometric viscosities below 250 Cp at processing temperatures and a good pot life. After complete curing, the PN polymers exhibited thermal stability above 500°C, a glass transition temperature (Tg) above the final postcure temperature of 380°C, and exceptional retention of structural integrity over a large temperature range. These results suggest that vanillin derived EBPN based resins are excellent candidates for use in a variety of applications where high temperature and mechanical stability is critical.

Enhancing high‐temperature mechanics and degradation for phthalonitrile resin via constructing rare earth oxide supported low melt‐point molten oxide

AbstractIn order to improve the comprehensive performance of thermosetting phthalonitrile resin (PN) composites, a novel molten hybrid (Nd2O3@DM35) was successfully prepared by loading Neodymium Oxide (Nd2O3) on the surface of low melt‐point molten oxide (DM35). In thermal gravimetric analysis, the addition of 30 wt% Nd2O3@DM35 postponed the temperature of 5% mass loss (T5%) of PN hybrid (PN‐NdD30) from 485 to 521°C. A series of thermal aging experiments were designed to prove the thermal stability of modified PN. The surface morphology of PN‐NdD30 was mostly maintained after thermal aging. Compared with pure PN, the flexural strength (FS) and interlaminar shear strength (ILSS) of PN‐NdD30 composites at room temperature increased by 31.4% and 32.8%, respectively. After aging at 400°C for 20 min, the FS and ILSS retention rates of PN‐NdD30 composites were 78.4% and 91.5%, respectively. In this work, the introduction of novel hybrid improved the thermal stability of PN composites, while enhancing their mechanical properties at different temperatures. Based on all the results, the heat resistance and mechanical mechanism of PN‐NdD30 composites were carefully analyzed.Highlights A molten hybrid was prepared by Nd2O3 and low melt‐point molten oxide. The novel hybrid can form a continuous protective layer at high temperatures. In the aging test, the mass loss of PN‐NdD30 was significantly reduced. Mechanical properties of PN composites at different temperatures were improved. A novel molten concept was introduced in the heat resistance modification of PN.

Study on the curing characteristics and properties of phthalonitrile resin cured with organic guanidine

Bisphenol A-based phthalonitrile resin was synthesized by nucleophilic substitution reaction from bisphenol A and 4-nitrophthalonitrile, and then the obtained resin was cured with sulfaguanidine as a novel curing agent. The curing characteristics, kinetics, thermal stability and dynamic mechanical property were studied by standard thermal analysis techniques including DSC, TGA, and DMA. The peak temperature of exothermic peak ( Tp) and apparent activation energy ( Ea) of sulfaguanidine cured phthalonitrile resin were 263.20°C and 76.6 kJ·mol−1 respectively, much lower than those of traditional aromatic diamine cured resin. Moreover, the resin cured by sulfaguanidine showed excellent thermomechanical properties and thermal stability. The glass transition temperature ( Tg) was 284.8°C, the initial thermal decomposition temperature ( Td,5%) was 439.6°C, and the char yield at 800°C was 62.1% in nitrogen atmosphere. To sum up, organic guanidine cured phthalonitrile resin exhibits excellent curing characteristics (low Tp and Ea) and high thermal properties, which provides a promising approach to preparing phthalonitrile resin with high comprehensive performance.

Curing behavior and thermal properties of phthalonitrile resins derived from benzyl alcohol

A series of phthalonitrile resins were synthesized through innovative reactions between compounds derived from benzyl alcohol and nitro functionalities. The synthesis commenced with the reaction of specific alcohols (4-hydroxybenzyl alcohol, vanillyl alcohol, and 1,4-benzenedimethanol) with 4-nitrophthalonitrile, resulting in the formation of three phthalonitrile monomers. These monomers were then cured using 4,4′-diaminodiphenyl ether as a curing agent, resulting in the phthalonitrile resins, namely BCDPN, XCDPN, and DBDPN. The investigation revealed that these resins possessed remarkable properties, particularly in terms of thermal stability and dynamic mechanical behavior. Notably, BCDPN exhibited superior thermal stability, achieving a Td10 % of 534 °C. XCDPN and DBDPN demonstrated outstanding dynamic mechanical properties, characterized by a storage modulus exceeding 3400 MPa. The synthesis approach, leveraging compounds derived from benzyl alcohol and nitro reactions, not only broadens the scope of raw materials but also offers novel and alternative preparation strategies for phthalonitrile resins. This study enhances the understanding of the curing behavior and thermal properties of these resins, providing valuable insights into their potential applications in high-performance polymer materials.

Fire behavior and post-fire residual tensile strength prediction of carbon fiber/phthalonitrile composite laminates

Carbon fiber/phthalonitrile (Cf/PN) composite has a high potential for applications in the aerospace sector because of the outstanding heat and flame resistance of phthalonitrile resin. Here we aim to evaluate the fire behavior of Cf/PN laminate under localized one-sided flame heating as well as the residual tensile performance. The residual tensile strength after quasi-isothermal pyrolysis in an inert environment decreases linearly with the increase in the pyrolysis degree. The temperature response and pyrolysis behavior are analyzed through a combination of experiments and finite element simulations, and the damage mode of the laminate structure is concluded through morphological observation after flame exposure and the surface axial strain field using digital image correlation. Eventually, the residual tensile strength of laminates with different thicknesses after different times of flame exposure was effectively predicted based on the numerical simulated pyrolysis degree distribution. This research supplies fundamental test data on the mechanical properties of Cf/PN laminates and is expected to provide guidelines for the engineering application of Cf/PN composites in thermal protection/load-bearing all-in-one structures.

High-performance C/C composites derived from phthalonitrile matrix CFRP via a few cycles of vacuum-assisted impregnation-carbonization

Novel approach of fabrication of carbon–carbon composites from carbon fiber reinforced plastics with phthalonitrile matrices was presented. Polymer composites were obtained by vacuum infusion, carbonized, and reimpregnated with following carbonization to reduce porosity of the resulting materials. The highest mechanical properties and lowest porosity were obtained when CFRP post-cured at 375 °C was taken initially. 4 cycles of impregnation-carbonization are sufficient to fabricate materials with the highest properties. Phthalonitrile resin transformations through curing, carbonization and graphitization using XRD, Raman spectroscopy, elemental analysis, FTIR and solid-state NMR were researched. TGA-MS revealed exposure of CH4, NH3, H2O, HCN, benzene and phenol gases during carbonization. Amorphous carbon materials were obtained after carbonization at 1000 °C with ID/IG = 2.38 and graphitization at 2200 °C resulted in formation of more structured carbon material with ID/IG = 0.63. Mechanical and thermal properties of the composites were determined at every step of the process.

An end-capping strategy for shape memory phthalonitrile resins via annealing enables conductivity and wave-absorption

Shape memory polymers (SMPs) with elevated switching temperatures and enduring thermal properties are highly desirable yet challenging in certain aerospace applications. In this study, high-temperature shape memory phthalonitrile resins (SMPNs) were developed using an end-capping strategy with the uniphthalonitrile (UPN) as the end-capping reagent to modulate the density of the cross-linked network. The resultant SMPNs exhibit a glass transition temperature (Tg) at approximately 300 °C, with a shape fixation rate of about 98 % and a shape recovery rate around 97 %. Importantly, these SMPNs also demonstrated exceptional thermal stability, with a thermal decomposition temperature exceeding 445 °C. Additionally, an oxyacetylene ablative test revealed the SMPNs' robust ablative resistance, as the linear ablation rate remained below 0.1 mm/s and the mass ablation rate was less than 0.1 g/s. The commendable shape memory performance and superior high-temperature resistance allowed the SMPNs to successfully undergo the shape recovery process when subjected to a butane flame. Furthermore, after a high-temperature annealing process, the SMPNs exhibited electrical conductivity due to graphitization, even possessing wave-absorbing properties within a specific frequency range. It is foreseeable that these multifunctional SMPNs will have extensive applications in the aerospace sector, given the advancement of smart structures.

Micro-fabrication of glassy carbon with low shrinkage and high char yield using high-performance photocurable phthalonitrile (PN) resins

Glassy carbons (GCs) are a significant class of materials that have attracted considerable attention in many scientific and technical fields due to their great thermal and chemical stability, excellent biocompatibility, and remarkable thermal and electrical conductivity. However, the thermal resistance and brittle nature of GCs pose limitations on their processing using conventional techniques such as melting extrusion or sintering. 3D printing as a rapidly developing technology advances product fabrication in prototyping and tooling provides a revolutionizing alternative of material processing with the advantage of accurately producing complex structures/shapes. This study demonstrates the micro-fabrication of GC objects based on novel photocurable high-performance phthalonitrile (PN) resins with a vat photopolymerization printing technology named as projection micro stereolithography (PμSL). In initial, soluble acrylate PN monomers are successfully developed and subsequently formulated into photopolymerizable resins. The resultant resins show excellent thermal and mechanical properties with Tg around 300 °C and flexural strength of 150 MPa after post thermal treatment. Being fabricated into 3D structures via PμSL printing, the obtained PN based objects are converted to GC products through pyrolysis in inert atmosphere with high char yield and low shrinkage. As a result, diverse microscale 3D GC objects are achievable and exhibit excellent structural integrity and fidelity. Our approach develops the micro-fabrication of dense and complex structured GC for the first time, providing a versatile functional platform for advancing next generation applications in medical tools, electrochemistry and precision micro-moulding as well as in energy and aerospace technologies.

Enhanced mechanical and thermal properties of phenolic-type phthalonitrile nanocomposites with fumed silica nanoparticles

Enhancing the mechanical properties and thermal stability of phthalonitrile polymers by hybrid modification holds significant importance in broadening their thermal-structural applications within high-temperature environments. Herein, fumed silica nanoparticles were considered as modifiers for a class of phenolic-type phthalonitrile resin, i.e., PN75, and their effects on mechanical properties and thermal stability were explored. First, contact angle tests (CA) were employed to show that the PN75 melt had good wettability on hydrophilic fumed silica (FS) and poor wettability on hydrophobic fumed silica (RFS). FS had a relatively satisfactory dispersion within PN75, which was indicated by scanning electron microscope (SEM), followed by FS/PN75 nanocomposites were prepared by melt blending under vacuum, with maximum FS addition 3 wt% of PN75. Second, the flexural strength and modulus of nanocomposites were increased by 23.5% and 11.9%. Finally, thermal stability of the FS/PN75 was promoted from 21.6% to 25.6% in char residue at 800 °C in the air atmosphere by the thermogravimetric analysis (TGA), which was contributed by the high heat-resistance and the shielding effect of FS. This work would inspire in-depth studies on modification and design of phthalonitrile-based hybrid composites for extreme thermal environment.

Rediscovering phthalonitrile resins: a novel liquid monomer towards high-performance resins

Phthalonitrile resins from a high-processability liquid monomer exhibit good thermal stability and flame retardancy.

Preparation and properties of bisphenol A polyetherketoneketone based phthalonitrile resins

AbstractA promising high temperature phthalonitrile (PN) resin composed of a polyetherketoneketone (PEKK) core bridged by two bisphenol A linkers and end capped with PN groups is presented. This PEKK‐PN resin was characterized via differential scanning calorimetry, thermogravimetric analysis, proton nuclear magnetic resonance spectroscopy, scanning electron microscopy, dynamic mechanical analysis, attenuated total reflection Fourier transform infrared, and rheometry. The PEKK‐PN resin was evaluated with two different compositions containing 1) 70:30 PEKK‐PN to bisphenol A PN (n = 0) and 2) pure PEKK‐PN. The 70:30 PEKK‐PN resin was mixed with bis[4‐(3‐aminophenoxy)phenyl]sulfone and exhibited a melt viscosity of 271 cP, much lower than the 657 cP viscosity of the pure PEKK‐PN mixture. Void‐free PEKK‐PN polymers were easily prepared by degassing and curing up to 380°C, resulting in fully crosslinked networks exhibiting thermal stability above 500°C and a 75% char yield. Additionally, the cured PEKK‐PN polymer samples displayed good mechanical integrity retaining 50% stiffness at 300°C. This combination of properties suggests these new PEKK‐PN resins are excellent materials for high temperature thermosets in composite applications.

Achieving high heat resistance for phthalonitrile/boron blends through formation of protective phases derived from boron powder

Phthalonitrile resins or its blends with high heat resistance are urgently demanded for spacecrafts that usually operate in extreme environment. Here, the heat resistance of phthalonitrile was significantly improved by introducing boron powders. The boron powders not only played a role in physically insulating oxygen from the matrix but also forming the boron oxide phase, which both retarded the thermal decomposition process of phthalonitrile resin at elevated temperatures. The results show that the as-prepared phthalonitrile/boron blend with 20.0 wt% boron exhibited high Td5% of 549 °C and 552 °C in air and N2 atmosphere, respectively. For the carbon fiber fabric reinforced phthalonitrile/boron composites, the flexural modulus and flexural strength were improved from 82.6 GPa to 778 MPa for phthalonitrile resin composite to 134.2 GPa and 978 MPa at 450 °C, respectively. This work demonstrates an efficient way to prepare phthalonitrile composites with excellent thermal stability and good mechanical performance.