Phthalonitrile Monomer Research Articles

Introducing rigid pyrimidine ring to improve the mechanical properties and thermal‐oxidative stabilities of phthalonitrile resin

In this study, a novel phthalonitrile monomer containing pyrimidine ring, 4,6‐bis[3‐(3,4‐dicya‐ nophenoxy)phenoxy]pyrimidine (BCPM), was successfully synthesized by nucleophilic substitution reaction with resorcinol, 4,6‐dichloropyrimidine and 4‐nitrophthalonitrile. The BCPM monomer was cured by different temperature programs with 4‐(aminophenoxy)phthalonitrile (APPH) as catalyst to give the polymers. The molecular structures of the BCPM monomer and the polymers were investigated by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Differential scanning calorimetric (DSC) analysis was performed to study the processability of the BCPM monomer, which showed a wide processing window of about 117°C. The mechanical properties and thermal‐oxidative stability of the polymer were characterized by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), respectively, which indicated that the polymers exhibited excellent storage modulus, high glass transition temperature over 400°C, and outstanding thermal stability. The polymers also have low water absorption capacity and are suitable for humid environments.

Phthalonitrile Resins Derived from Vanillin: Synthesis, Curing Behavior, and Thermal Properties

Vanillin was used as sustainable source for phthalonitrile monomer synthesis, and allyl/propargyl ether moieties were introduced to improve the processability at the minimal cost of thermal properties. The synthesis route was optimized to minimize side-reactions and simplify post-processing, and the monomers were obtained in high purity and good yields. The curing behavior, mechanism, and processability of the monomers were studied, and the thermal properties of cured polymers were evaluated. Of the two monomers, the allyl ether-containing one exhibited a wide processing window of 185 °C, and was mainly cured into phthalocyanine and linear aliphatic structures through self-catalytic curing process. Also, the glass transition temperature was higher than 500 °C. In contrast, the propargyl ether-containing monomer could only be partially cured, and heat resistance was found to be compromised. Compared with traditional petroleum-based phthalonitrile resins, the bio-based monomers could be cured without the addition of catalysts, and improvement in processability was achieved at no cost of thermal performances.

A prospective partial bio-based diamine-adenine-monomer platform for high performance polymer: A case study on phthalonitrile resin

A novel partial bio-based molecular design platform for high performance polymer (HPP) namely diamine-adenine-monomer platform (DAAMP) was suggested and discussed in this paper. Aimed at introducing the adenine moiety into backbone of HPP and endowing great wide molecular tailorability, DAAMP was synthesized via a nucleophilic displacement between 6-chloropurine and various diamines. Phthalonitrile (PN) resin is a typical class of HPP. To verify the feasibility of DAAMP for HPP design, two new phthalonitrile monomers based on two different diamine namely DAAMP-PN were synthesized. The chemical structures of synthesized monomers were confirmed by Fourier Transform Infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR). The two new DAAMP-PNs based on different diamines showed an obvious difference in thermal polymerization behavior. Multiple hydrogen bonding was exhibited in DAAMP-PN system. And the prepared DAAMP-PN polymer showed high glass transition temperature, excellent thermal and thermo-oxidative stabilities. The results demonstrated that DAAMP is a promising building-block for HPP design with flexible molecular tailorability.

Synthesis of cardanol‐based phthalonitrile monomer and its copolymerization with phenol–aniline‐based benzoxazine

ABSTRACTThe cardanol‐based phthalonitrile (PN) monomer was successfully produced via the nucleophilic substitution reaction of cardanol with 4‐nitrophthalonitrile in potassium carbonate media. The conventional methods were employed to predict the chemical structure. The influence of long alkyl chains of cardanol was observed on the thermomechanical properties, recorded values were much below than the poly(Baph) standards. However, the thermal stabilities were recorded in good agreement to PN resin values. Furthermore, the 100 kGy dose of Co60 irradiation does not show any remarkable changes in the studied properties. The copolymers from P‐a benzoxazine and cardanol‐based PN (CPN) on the different wt % blending were prepared. The curing behavior and mechanism of the monomer blends were analyzed. The curing of CPN was improved in the presence of active hydrogen produced from the P‐a polymerization. The T g and thermal properties of the copolymer were much better than the neat poly(P‐a). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47505.

Synthesis and properties of pyrazine-based oligomeric phthalonitrile resins

The pyrazine-based oligomeric phthalonitrile (PN) monomer, 2,6-bis[3-(3,4-dicyanophenoxy)phenoxy]pyrazine (BCPP), was synthesized from the reaction of an excess amount of resorcinol with 2,6-dichloropyrazine in the presence of potassium carbonate, followed by end-capping with 4-nitrophthalonitrile in a two-step, one-pot reaction. 4-(Aminophenoxy)phthalonitrile was applied to promote the curing reaction. The curing behavior was investigated by differential scanning calorimetry and rheological behavior, showing a wide processing window of 94°C, a complex viscosity of less than 1.5 Pa·s and a lower reaction activation energy of 32.57 kJ mol−1. The structure of the BCPP monomer was confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The unit cell was determined to be tetragonal system by wide-angle X-ray diffraction. The monomer was cured to yield cross-linked polymers, which exhibited a high initial storage modulus, excellent glass transition temperature, outstanding thermal stability, and low water uptake.

Low melting phthalonitrile resins containing methoxyl and/or allyl moieties: Synthesis, curing behavior, thermal and mechanical properties

Low melting phthalonitrile monomers containing allyl and/or methoxyl groups were designed, synthesized and characterized. In order to evaluate their potential application in phthalonitrile resins, these monomers were blended with 1,3-bis(3,4-dicyanophenoxy)benzene and 4-(4-aminophenoxy)phthalonitrile, then cured into polymers. Curing mechanisms of different prepolymers were proposed and compared, and processability, thermal and mechanical properties were characterized. The introduction of methoxyl units was found to postpone the curing, and thermal properties were slightly compromised. On the contrary, the usage of allyl was beneficial to both processability and thermal properties. More importantly, the impact strength for allyl-containing polymers could be as high as 13.63 kJ m−2, indicating such resin could be applied as high temperature structural composite matrices.

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.

Copolymerization of mono and difunctional benzoxazine monomers with bio-based phthalonitrile monomer: Curing behaviour, thermal, and mechanical properties

The eugenol based phthalonitrile (EPN) monomer was successfully copolymerized with mono and difunctional benzoxazine (P-a and BA-a) monomers via concerted catalysis polymerization. The loading of EPN in benzoxazine monomers was varied from 10 to 40 wt% and impacts of loading on thermal, thermomechanical and mechanical properties were studied. The FTIR analysis confirmed that both poly(P-a/EPN) and poly(BA-a/EPN) copolymers can be completely cured without the addition of curing additive. The addition of the bio-based EPN monomer enhanced the curing peak temperatures and reduced the curing reaction enthalpies. Initially, OH groups were produced from the oxazine ring opening polymerization of benzoxazine and they enhanced the curing of EPN. The thermal stabilities, as well as the stiffness and Tg of the copolymers, were much higher as compared to the neat polymers. Highest values were seen on the 40 wt% loading of EPN monomer in the copolymers. Moreover, the difunctional benzoxazine based copolymer showed higher enhancements in the properties as compared to the mono-functional benzoxazine based copolymer. The decline was seen in the flexural properties as EPN monomer contains the flexible chain in the structure. The morphological changes supported all the claims for the copolymers. The prepared copolymers can be used as a high performance thermosetting resin.

Understanding of the polymerization mechanism of the phthalonitrile-based resins containing benzoxazine and their thermal stability

As a unique class of high-performance phthalonitrile-based resins, phthalonitrile containing benzoxazine resin has attracted increasing interests in a widen application fields including aerospace, electronic packaging materials and flameresistant materials in marine. In order to reveal the polymerization mechanism of nitrile groups in the presence of benzoxazine, model experiments were designed and performed with three model compounds, which were synthesized according to the structures of the ring-opened benzoxazine rings. Model compounds with phenolic hydroxyl groups, amine structures and both of them were blended with bisphenol A phthalonitrile monomers and their curing behaviors were investigated by DSC and FTIR. Also, the possible polymerization process was proposed and discussed in detail. Results indicated that the polymerization of nitrile was promoted by the synergistic catalysis effects of the amine structures and the active hydrogen generated from the ring-opening of benzoxazine rings. The nitrile groups were firstly triggered by the lone pair electrons in amine structures and then the further polymerizations were promoted by the phenolic hydroxyl groups. Moreover, it was found that the compounds with well-ordered structures of phenol hydroxyl groups and amine structures exhibited relatively weak acceleration on the trigger polymerization of nitrile groups, while higher subsequent polymerization rate, in comparison with the other model compounds, which can be ascribed to their space configuration and the steric hindrance effects. Additionally, the thermal stability of the resulted polymers with various model compounds was studied to confirm the proposed polymerization mechanism and the final polymerization structures.

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.

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.

Low‐viscosity and soluble phthalonitrile resin with improved thermostability for organic wave‐transparent composites

ABSTRACTHigh processing viscosity and poor solubility limit the application of heterocyclic polymers for fabricating organic wave‐transparent composites for aerospace applications. In this paper, a novel resin, poly(phthalazinone ether bisphenol fluorene) encapped with phthalonitrile (PPEBF‐Ph), was synthesized and used as the matrix. Biphenol‐based phthalonitrile monomer BP‐Ph was also synthesized and blended with PPEBF‐Ph to further lower the processing viscosity. Solubility tests showed that the resin was soluble in dimethylformamide, N,N‐dimethyl acetamide, N‐methylpyrrolidone, dimethyl sulfoxide, chloroform, and other solvents. Differential scanning calorimetry and rheological studies revealed that the mixed resins exhibited low processing viscosity and a wide processing window below the gel temperature. Thermogravimetric analysis indicated that the cured resins were stable below 510–530 °C under nitrogen atmosphere after 6 h of curing (decreased by 40–60% compared with previous reports on phthalonitrile resin). In air, the char yields of the resins reached 20–30% when heated at 800 °C. The composites were reinforced by a quartz fiber cloth and exhibited a dielectric constant of 2.94–3.27 in an electromagnetic field with frequency ranging from 8 to 18 GHz. Retention of the bending modulus exceeded 70% at 400 °C according to dynamic mechanical analysis, indicating excellent mechanical stability was obtained. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45976.

Synthesis and properties of a novel naphthyl-containing self-promoted phthalonitrile polymer

A novel naphthyl-based self-promoted phthalonitrile monomer, 4-(8-amino-2-naphthyloxy)phthalonitrile (8-ANP), was successfully synthesized via nucleophilic substitution reaction through a one-pot reaction, and it exhibited desirable processing feature with a wide process window (temperature between the melting point and the cure temperature) and low complex viscosity. The activation energy ( Ea) value of the self-promoted curing reaction was ascertained using integral isoconversional Starink method. Even without post cure at high temperature for a long time, the properties of 8-ANP polymers were still outstanding, which exhibited high glass transition temperatures, high storage modulus, low average coefficient of thermal expansion, and excellent thermal and thermo-oxidative stabilities.

Synthesis of benzophenone-center bisphenol-A containing phthalonitrile monomer (BBaph) and its copolymerization with P-a benzoxazine

The benzophenone-center bisphenol-A containing phthalonitrile monomer (BBaph) was successfully produced by a nucleophilic substitution reaction of 4,4′-difluorobenzophenone with 4-nitrophthalonitrile and bisphenol-A in the presence of potassium carbonate. The chemical structure of the synthesized monomer was confirmed by 1H nuclear magnetic resonance (1H NMR), 13C NMR, and Fourier transform infrared spectroscopy (FTIR). The curing study of monomer was evaluated by the FTIR and DSC curves. The poly(BBaph) was subjected to gamma-ray irradiation with 100kGy dose of 60Co gamma radiation. The variation in chemical structure, mechanical, thermomechanical and thermal properties of poly(BBaph) was evaluated by FTIR, flexural, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA), respectively. All results confirmed very minute deviation in the estimated properties before and after radiation. The BBaph monomer was blended with typical mono-functional benzoxazine (P-a) in different weight ratios. The DSC, DMA, and TGA tests were performed to study the properties of copolymers. The high glass transition temperature (164–227°C), and stiffness values (2.72–3.03GPa) was observed for the copolymers. The thermal stability was also improved after the loading of BBaph in P-a, recorded values were in the range of 367–408°C, and 46.1–58.7% for 5% weight loss temperature and char yield at 800°C, respectively.

Novel amino-containing fluorene-based bisphthalonitrile compounds with flexible group

A series of amino-containing fluorene-based bisphthalonitrile (AFPN) monomers with alkyl or alkoxy groups were successfully produced by the reaction of 4-nitrophthalonitrile with 9, 9-bis (3-alkyl (or alkoxy)-4-aminophenyl)-2, 7-dihydroxylfluorene in the presence of potassium carbonate by a nucleophilic substitution reaction. The chemical structures of the synthesized monomers were confirmed by the Fourier transform infrared (FTIR), proton nuclear magnetic resonance, and carbon-13 nuclear magnetic resonance analyses. The synthesized monomers’ curing behaviors were evaluated by FTIR and differential scanning calorimetry, and a rheological analysis was performed to evaluate their respective processabilities. Moreover, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) were performed for the thermomechanical, thermal, and thermo-oxidative analyses of the polymers. The results confirmed that the newly prepared phthalonitrile (PN) monomers with alkyl or alkoxy groups exhibited a self-promoted curing behavior. The rheological analysis suggested that the processing windows of the synthesized monomers were wider than that of APFN monomer bearing no flexible group. DMA and TGA revealed that the cured polymers exhibited high glass transition temperature (358–416°C) and the char yields at 800°C under nitrogen were between 70% and 77%. Moreover, the introduction of alkyl or alkoxy groups into the PN monomers’ backbones slightly reduced the thermal stability of the resulting polymers.

Novel phthalonitrile-based composites with excellent processing, thermal, and mechanical properties

Phthalonitrile resins exhibit excellent thermostability and mechanical strength after curing. However, poor processability made them difficult to fabricate fiber-reinforced composites with desirable integrated performance. In this article, a novel mixed phthalonitrile resin was developed to be used as the matrix for glass fiber–reinforced laminates. Poly (aryl ether nitrile phthalazinone) oligomer end-capped by phthalonitrile units (PPEN-PN) was firstly designed and blended with bisphenol-based phthalonitrile monomers (BP-PN) (Figure 1), which were obtained according to the literature procedure. A novel mixed curing agent (zinc chloride and 4,4-diamine-diphenylsulfone) was also exploited to accelerate curing rate of the resins. Solubility tests, differential scanning calorimetry and rheological studies revealed that the mixed resins exhibited good processability with low processing viscosity. Thermal gravimetric analysis indicated that the cured resins were stable below 530 to approximately 570 °C in nitrogen atmosphere after low-cost curing procedure. In air, char yields of the resins were between 30 to approximately 40% when heated to 800 °C. The laminates reinforced by E-glass fiber cloth possessed a bending strength of 668 MPa with interlaminar shear strength of 84.6 MPa at room temperature. 50% of the strength and modulus was maintained when heated to 400 °C. Consequently, this type of laminates may be potential candidates for aerospace applications.

Preparation and properties of phthalonitrile resins promoted by melamine

Melamine, which has a unique structure and is known as an important raw material, was first employed as a curing agent to promote the curing reaction of phthalonitrile monomer 1,3-bis(3,4-dicyanophenoxy)benzene. Rheometric measurements and differential scanning calorimetry showed that the blends exhibited wide processing windows (∼80°C). The thermal properties of the final cured polymers were monitored by thermogravimetric analysis, and the results revealed that the polymers had outstanding thermal stabilities. Dynamic mechanical analysis indicated that the glass transition temperature of the final cured polymers exceeded 480°C.

Flame-retardant carbon fiber reinforced phthalonitrile composite for high-temperature applications obtained by resin transfer molding

Carbon fiber reinforced phthalonitriles obtained by resin transfer molding have been reported for the first time. Special formulation based on silicon-and phosphorus-containing phthalonitrile monomers has been developed to yield a composite with retention of mechanical properties at 300 °C and remarkable flame-retardant properties (LOI > 80%).

Improving the curing process and thermal stability of phthalonitrile resin via novel mixed curing agents

AbstractHigh curing temperature (including post‐curing temperature) and long curing time of phthalonitrile resins make them thermally stable but difficult to process. In this paper, novel mixed curing agents (CuCl/4,4′‐diaminodiphenylsulfone (DDS) and ZnCl2/DDS) were firstly designed for solving these problems. Bisphenol‐based phthalonitrile monomer (BP‐Ph; melting point: 228–235 °C) was synthesized and used as the curing precursor. Differential scanning calorimetry results indicated that BP‐Ph cured with CuCl/DDS and ZnCl2/DDS exhibited curing temperatures close to the melting point of BP‐Ph with curing ending temperatures of 225.4 and 287.1 °C, respectively. Rheologic investigations demonstrated obvious curing reactions of BP‐Ph occurred with the mixed curing agents at 220 °C. Thermogravimetric analysis showed that BP‐Ph cured by CuCl/DDS or ZnCl2/DDS maintained 95% mass at 573 or 546 °C, respectively, at a post‐curing temperature of 350 °C for 2 h. Reasonable long‐term thermo‐oxidative stability was also demonstrated. When the post‐curing temperature decreased to 290 °C, char yield at 800 °C of BP‐Ph cured by CuCl/DDS was 77.0%, suggesting the curing procedure can be milder when using mixed curing agents. © 2017 Society of Chemical Industry