Phthalonitrile Polymers Research Articles

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.

Structural design and synthesis of naphthalene‐containing phthalonitrile polymer with excellent processability and high temperature properties

AbstractCurrently, there is limited literature on the introduction of naphthalene ring into phthalonitrile. In this study, we have successfully synthesized a novel phthalonitrile monomer (CPND) by incorporating a symmetrical rigid naphthalene ring structure, long flexible chains, and high‐density cyano groups into the resin. The monomer is being cured with two different agents and procedures to investigate the impact of curing agent structure and ramp‐up procedure on polymer properties. The structure of the monomer is being verified using nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR), and wide‐angle X‐ray diffraction (WAXD). Differential scanning calorimetry (DSC) results reveal that the monomer has a low melting point of 111°C, making it easily processable. After mixing with the curing agent in the appropriate proportion, it has a calculated processing window of 129–135°C. Thermogravimetric analysis (TGA) reveals that the polymers exhibit remarkable thermal stability, with all T5% above 470°C under a nitrogen atmosphere. Additionally, the results obtained from dynamic mechanical analysis (DMA) indicate that the polymer, which is cured using APPH as a curing agent, displays favorable thermo‐mechanical properties. The storage modulus of the polymers at room temperature is all higher than 3330 MPa, respectively. Moreover, the glass transition temperature is found to be higher than 400°C, signifying the excellent thermo‐mechanical properties of the polymer.

Self-catalytic phthalonitrile polymer with improved processing performance and long-term thermal stability

Phthalonitrile monomer with alkyl, pyrimidine, and amino is successfully prepared by nucleophilic substitution. The monomer is cured by autocatalysis of active hydrogen in the amino group, in order to obtain polymers through different temperature procedures. The low melting point (96°C) and curing kinetics of the monomer are analyzed by DSC, which manifest a processing window of 163°C. With lower energy barriers to overcome, the apparent activation energy ( E a) is 59.6 kJ mol−1 after fitting and calculating, signifying that the monomers are easier to process into polymers. This study focuses on the usefulness of the polymer, especially the long-term thermal stability by the comparison of numerous commonly used polymers. The consequence demonstrates that the polymer could be used for long periods at 300°C, keeping weight loss within 5 wt.% for 6 h. The advantage of long-term usage at high temperatures has not been proved in previous works on phthalonitrile polymer. Moreover, the thermal and thermal-mechanical stability are examined through TGA and DMA. The results indicate preferable thermal properties, that the glass transition temperature is up to 400°C.

Toughening mechanism of phthalonitrile polymer: MD simulation and experiment

Based on the demand for materials in the aerospace field, we are researching the brittleness problem of phthalonitrile resin (PN75), a high-temperature resistant resin material. Combining molecular dynamics simulations with experiments in time-consuming and costly studies has become a meaningful way to reduce research and development cycle time and cost. In a world where high-performance computer simulations are capable of enormous computational scales with guaranteed reliability, experiments and characterization at the atomic-molecular scale are still challenging tasks. Revealing microscale mechanisms through atomic simulations and providing guidance for laborious, time-consuming, and expensive experiments is one of the current scientific hotspots. The free volume pore distribution of PN75 was analyzed using molecular dynamics (MD) simulations to reveal the primary mechanism of PN75 during toughening. Improving the scalability of the free volume cavity of PN75 creates an appreciable energy dissipation mechanism. The combination of experimental and MD simulation results verifies the usefulness of simulation as a guide for experiments. MD simulations can reduce complex experimental and characterization efforts, reveal experimental mechanisms at the nanoscale, and guide the design of polymers.

Synthesis and Properties of Phthalonitrile Polymer with a Novel Piperazine Structural Curing Agent

AbstractA novel autocatalytic phthalonitrile (PN) monomer containing piperazine structure, namely 4‐[1‐(4‐aminophenyl)‐4‐(4‐phenyl)piperazine‐oxy]phthalonitrile (APPN), is synthesized from the nucleophilic substitution reaction of 1‐(4‐Aminophenyl)‐4‐(4‐hydroxyphenyl)piperazine and 4‐nitrophthalonitrile. The structure of the APPN monomer is characterized by Nuclear Magnetic Resonance (NMR) spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy. The novel 4‐nitrophthalonitrile end‐capped compound APPN is firstly used to promote the curing reaction of PN monomer 1,3‐bis(3,4‐dicyanophenoxy)benzene (m‐BDB). Thermogravimetric Analysis (TGA) and Dynamic Mechanical Analysis (DMA) showed that the PN resin in the presence of 10 % of APPN possessed outstanding thermal and thermo‐oxidative stabilities as well as good mechanical properties, better than the properties of those with 20 % of APPN and 10 % of APPH. Its glass transition temperature (Tg) is higher than 400 °C, and the polymer loses 5 % of its weight (T5%) at 524 °C and shows a storage modulus of 1373 MPa at 400 °C.

Improved toughness of phthalonitrile composites through synergistic toughening methods

Brittleness has long been a trouble for the application of phthalonitrile polymers in high temperature structural composites. In this work, crosslinkable poly(aryl ether nitrile) and insoluble polyimide particles were first selected as binary toughening modifiers for synergistic toughening of phthalonitrile composites, respectively. Various mechanical measurements and thermal tests were adopted to systematically evaluate the toughening effects as well as heat resistance. The optimized composites exhibited GIC of 659.7 J/m2 and GIIC of 907.1 J/m2, while ILSS increased to 78.6 MPa. More importantly, its glass transition temperature was 449 °C, which was only slightly lower than the blank contrast. Later, the mechanism for this synergistic toughening was proposed and discussed.

Curing behavior studies of phenol-containing phthalonitrile monomer for advanced composite materials

Phenol-containing phthalonitrile polymer is a novel type of autocatalytic phthalonitrile thermoset with outstanding thermal performance. In this work, the curing behavior of phenol-containing phthalonitrile monomer was studied by differential scanning calorimetry. Based on the isoconversional principle, the activation energy was calculated as 63±6 kJ/mol. It is significantly lower than the reported that of phenol catalyzed, indicating a strong reactivity of phenol-containing phthalonitrile monomer. Additionally, the reaction model was judged to be autocatalytic and the remaining kinetic parameters were calculated by linear regression method. By comparing the experimental data with the kinetic mathematic model, the accuracy of the curing kinetic equation was verified. Moreover, the curing kinetic equation was adopted to predict the curing time for phenol-containing phthalonitrile polymer to fully solidify under a constant temperature, which is of great significance for the application of phenol-containing phthalonitrile polymer.

SiBCN ceramic precursor modified phthalonitrile resin with high thermal resistance

In order to expand the application of phenolic-type phthalonitrile resin in high-temperature fields, a series of organic–inorganic hybrid materials have been prepared via conventional blending and doping method. The chemical transformations were monitored by various measurements, while the curing behavior was evaluated by differential scanning calorimetry (DSC), and these new blends could be also cured under auto-catalytic process. The onset polymerization exothermic temperature shifted to lower temperatures (195.3°C). Later, the compatibility within the cured products was analyzed by using energy dispersive spectrometer (EDS) and scanning electron microscope (SEM), where no phase separation occurred between the ceramic domain and the phthalonitrile polymer. Upon curing, the thermal properties of the polymers were characterized by dynamic thermomechanical analysis (DMA) and thermogravimetric analysis (TGA), where enhanced heat resistance and thermal stability were discovered, The blends residual weight (Cy) value was 57.6% with 15 wt.% SiBCN at 1000°C. And when blended with SiBCN precursor, no peak or onset point could be observed in the temperature range (50 to 500°C), which indicated the glass transition temperature greater than 500°C. Additionally, the dielectric properties were evaluated. And when the content was 5 wt.%, the blends dielectric loss was 0.0043 and the permittivity was 4.31. The above results indicated that the introduction of ceramic precursors could enhance the thermal performance of phthalonitrile polymers, consequently the hybrid materials shown great potential in the application of higher temperature fields.

Chemical structure and curing dynamics of bisphenol S, PEEKTM‐like, and resveratrol phthalonitrile thermoset resins

AbstractThis effort provides a multifaceted analysis of the structural changes and material dynamics of thermally driven softening and curing of three distinct phthalonitrile (PN) resins that cross‐link into thermally stable and oxidation‐resistant thermosets. Although this material system has yielded a large subset of fire‐retardant composites that require facile processing and low‐temperature curing, to date, insufficient information had been available on the fundamental processes that drive their softening and curing stages. Our approach conducted a complementary analysis the chemistry, monomer mobility, and rheology of three PN polymers in order to correlate the curing processes with corresponding structural and behavioral transformations of thermosets. We focused on PNs with a bisphenol S backbone, a bisphenol A (PEEKTM‐like) backbone, and a resveratrol backbone. We relied on quasi‐elastic neutron scattering (QENS) in order to analyze the in situ dynamics and self‐diffusion properties of PN monomers, and to track changes in their mobilities during cross‐linking and staging. Our analysis facilitates proper control over the staging and final curing of these resins and enables more efficient processing of these thermosets.

Thermally Activated Structural Changes of a Norbornene–Benzoxazine–Phthalonitrile Thermosetting System: Simple Synthesis, Self-Catalyzed Polymerization, and Outstanding Flame Retardancy

Phthalonitrile polymers exhibit many attractive advantages including high thermal and mechanical properties, low water absorptivity, and excellent flame retardancy. However, the poor processability...

Synthesis and properties of a high‐performance pyrimidine‐containing self‐catalyzed phthalonitrile polymer

ABSTRACTA self‐catalytic monomer of phthalonitrile, 2‐amino‐4,6‐bis[3‐(3,4‐dicyano‐phenoxy)phenoxy] pyrimidine (ACPP), was synthesized by a one‐pot method with resorcinol, 2‐amino‐4,6‐dichloropyrimidine, and 4‐nitrophthalonitrile. The chemical structure of the ACPP monomer was characterized by Fourier transform Infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy. The curing behavior of ACPP monomer was studied by differential scanning calorimetric, which indicated that the ACPP monomer had a low melting point (84 °C) and revealed an autocatalytic reaction and tremendously wide processing window (193 °C). Wide‐angle X‐ray diffraction (WAXD) and FTIR analyses were employed to explore the microstructure of the ACPP polymers. The properties of the three polymers with different curing procedures were investigated, which implied that the ACPP polymers exhibited excellent thermal stability, high modulus, superior glass‐transition temperature (Tg > 400 °C), and low water absorption with the increase in curing extent. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2287–2294

Enhanced thermal property via tunable bisphenol moieties in branched phthalonitrile thermoset

The development of high-temperature resistant polymers and their composites is of particular interest because of their ever-growing applications. Herein, a family of branched phthalonitrile resins based on different bisphenols (Hydroquinone, 4,4′-Biphenol, m-Dihydroxybenzene, 1,6-Dihydroxynaphthalene, 2,6-Dihydroxynaphthalene) and phenyl-s-triazine, endcapping with 4-nitrophthalonitrile were prepared via a convenient condensation polymerization procedure. The relationship among bisphenol structures, thermal properties and mechanical properties were investigated in details. By incorporating the thermally stable phenyl-s-triazine segment into the branched phthalonitrile's backbone, the overall Tg (glass transition temperature) and Td (5% thermal degradation temperature) of the derived polymers were significantly improved. The resins were thermally cured to networks with 4,4′-diaminodiphenyl sulfone (DDS) as curing agent. The resulting networks exhibited high thermal resistance, indicated by Tg surpassing 500 °C and Td as high as 575 °C. Additionally, the composites exhibited high mechanical properties and dielectric properties stability at 500 °C. The results suggested the merits of branched phthalonitrile polymers for applications in high-temperature resistant polymers and composites.

Thermal and oxidative behavior of a tetraphenylsilane-containing phthalonitrile polymer:

Phthalonitrile polymers have potential for high-temperature applications in polymer matrix composites as electronic encapsulation compounds. To investigate the effect of inclusion of an organosilic...

Thermal and oxidative behavior of a tetraphenylsilane-containing phthalonitrile polymer

Phthalonitrile polymers have potential for high-temperature applications in polymer matrix composites as electronic encapsulation compounds. To investigate the effect of inclusion of an organosilicon moiety, a tetraphenylsilane-containing phthalonitrile monomer was synthesized in high yields. The monomer possessed a high melting point of 222–223°C, while no hydrolytic sensitivity was observed. Cured polymers exhibited glass transitions in the range of 290–325°C and coefficients of thermal expansion of 73–77 µm/(m °C). In thermogravimetric analysis (TGA), 5 wt% loss was observed at 482–497°C and 519–526°C, under air and nitrogen, respectively. Infrared (IR)-TGA of evolved gases revealed multiple degradations in both nitrogen and air. The material possessed good thermo-oxidative stability (TOS) when aged in air at 250°C. After aging for 5000 h, oxidative degradation was characterized using Fourier transform IR microscopy, energy dispersive spectroscopy, optical microscopy, and Knoop hardness testing. Four zones were identified in aged samples. The cleavage of Si-phenyl bonds and the formation of Si–O phases and carbonyl groups were observed.

Synthesis and properties of a novel high-temperature vinylpyridine-based phthalonitrile polymer

A novel vinylpyridine-based phthalonitrile monomer, 2,6-bis[3-(3,4-dicyanophenoxy)styryl]pyridine (BDSP), was resoundingly produced by a nucleophilic substitution reaction of 2,6-bis(3-hydroxystyryl)pyridine with 4-nitrophthalonitrile in the presence of potassium carbonate. The chemical structure of the synthesized BDSP was confirmed by proton (1H) and carbon (12C) nuclear magnetic resonance (NMR) as well as Fourier transform infrared (FTIR) analysis. The curing behavior of BDSP was investigated by FTIR and differential scanning calorimetry (DSC) analyses. The resin showed a low complex viscosity in the wide processing window between the monomer melting temperature and the curing temperature of the polymer, as discovered by rheological analysis. In addition, the properties of the polymer were studied by thermal gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Based on the test results, the BDSP polymer demonstrated superior processing performance, excellent thermal stability, outstanding mechanical properties, and low water uptake, and these advanced performance characteristics are critical to many fields.

The effect of thermal treatment on the decomposition of phthalonitrile polymer and phthalonitrile-polyhedral oligomeric silsesquioxane (POSS) copolymer

Phthalonitrile polymer and phthalonitrile-polyhedral oligomeric silsesquioxane (POSS) copolymer were sintered at 500 °C, 600 °C, or 800 °C. The samples before and after sintering were evaluated by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) coupled to FT-IR (TG-FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results suggest that phthalonitrile-polyhedral oligomeric silsesquioxane copolymers have better thermal stability than phthalonitrile polymers. After sintering at 800 °C, the phthalonitrile polymers decomposed completely while the phthalonitrile-polyhedral oligomeric silsesquioxane copolymers retain their original structure. The presence of the rigid POSS structure in the copolymer may limit the thermal movement of polymer chains at higher temperatures, thereby increasing the intermolecular forces between polymer chains. Moreover, POSS generates spatial steric hindrance, further restraining movement of chains and hindering degradation of labile groups; the overall effect is to improve the thermal stability of the composite under higher temperatures.

Curing behavior and properties of benzoxazine‐co‐self‐promoted phthalonitrile polymers

ABSTRACTA new high‐performance copolymer was successfully obtained via concerted catalysis polymerization of mono‐functional benzoxazine (P‐a) and self‐promoted 4‐aminophenoxy phthalonitrile (4‐APN) monomers. The FTIR and DSC curves of the P‐a/4‐APN in different blend ratios suggested that the monomer blends can be completely cured without the addition of curing additive. The P‐a/4‐APN copolymers were cured at relatively lower curing temperatures and time. The TGA curves revealed that the P‐a/4‐APN copolymers have good thermal stability in terms of T5, T10, and char yield. A gradual increase in the glass transition temperature (Tg) values and decline were seen in the storage modulus as the loading of 4‐APN was increased from 10 to 30 wt % in the copolymer. The SEM analyses showed that copolymer's fracture surface is dendritic, showing the stress has been dispersed to a certain extent. The study revealed that the poly(P‐a/4‐APN) copolymer have much better thermal stabilities than the poly(P‐a), and the prepared copolymer can be used as a high‐performance thermosetting resin. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46578.

Bio-based phthalonitrile compounds: Synthesis, curing behavior, thermomechanical and thermal properties

Two bio-based phthalonitrile (PN) monomers, eugenol-based phthalonitrile (EPN) and guaiacol-based phthalonitrile (GPN), were successfully synthesized by the reaction of 4-nitrophthalonitrile with eugenol and guaiacol derived from clove and lignin, respectively, in the presence of potassium carbonate via nucleophilic substitution reaction. Their chemical structures were confirmed by the Fourier transform infrared spectra (FTIR), hydrogen and carbon nuclear magnetic resonances (1H and 13C NMR), and elemental analysis. The curing behavior of the blends of the prepared PN monomers with 10 wt% of 4-(4-aminophenoxy)-phthalonitrile (4-APN) as curing agent was evaluated by FTIR and differential scanning calorimetry (DSC), while rheometer was used to analyze the processability of the blends. Moreover, the thermomechanical and thermal properties of the polymers were studied by dynamic mechanical analyzer (DMA) and thermogravimetric analysis (TGA). The results confirmed that the bio-based PN monomers and its blends show low melting temperatures, wide processing windows (>186 °C), and low melt viscosity (<0.03 Pa·s). The cured bio-based PN resins exhibited higher glass transition temperature and better thermal stability and toughness than those of typical bisphenol A-based phthalonitrile polymer. Meanwhile, the phthalodinitrile resins form a homogeneous, void-free network structure, which also confirm the excellent thermal and mechanical properties of the polymers.

Toward advanced gamma rays radiation resistance and shielding efficiency with phthalonitrile resins and composites

Abstract The phthalonitrile resins have claimed the leading place in the field of high performance polymers thanks to their combination of outstanding properties. The present work explores for the first time the gamma rays radiation resistance and shielding efficiency of the phthalonitrile resins and its related tungsten-reinforced nanocomposites. The primary goal of this research is to define the basic behavior of the phthalonitrile resins under highly ionizing gamma rays. The obtained results confirmed that the neat phthalonitrile resins can resist absorbed doses as high as 200 kGy. Meanwhile, the remarkable shielding efficiency of the phthalonitrile polymers was confirmed to be easily improved by preparing lead-free nanocomposites. In fact, the gamma rays screening ratio reached the exceptional value of 42% for the nanocomposites of 50 wt% of nano-tungsten loading. Thus, this study confirms that the remarkable performances of the phthalonitrile resins are not limited to the thermal and mechanical properties and can be extended to the gamma rays radiation and shielding resistances.

A novel high temperature vinylpyridine-based phthalonitrile polymer with a low melting point and good mechanical properties

This article is the first report on a phthalonitrile monomer containing vinyls in the main chain.