Novel self-promoted phthalonitrile monomer with siloxane segments: synthesis, curing kinetics, and thermal properties

In the study, we synthesize a novel auto-catalytic phthalonitrile monomer containing siloxane segments and secondary amino groups. The phthalonitrile monomer has good processability. And the new polymer shows a higher Tg.

A theoretical insight into the curing mechanism of phthalonitrile resins promoted by aromatic amines

High-temperature phthalonitrile resins have a wide range of applications, and understanding their curing mechanism is of great importance for academic research and engineering applications. However, the actual curing mechanism is still elusive. We presented a density functional theory study on the curing mechanism of phthalonitrile resins promoted by aromatic amines using phthalonitrile and aniline as the model compounds. We found that the rate-determining step is the initial nucleophilic addition of amines with nitrile groups on phthalonitrile to generate an amidine intermediate. The amines play a vital role in the H-transfer promoter throughout the curing reaction. The amidine and isoindoline are the critical intermediates, which can readily react with phthalonitrile through 6-membered transition states. The intramolecular cyclization of amidine intermediates is the vital step in forming isoindoline intermediates, which can be significantly promoted by amines. The proposed curing reaction pathways are kinetically more favorable than the previously reported ones, which can account for the formation of triazine, polyisoindoline, and phthalocyanine and provide a molecular-level understanding of the curing reaction.

A new molecular design platform for high-performance polymers from versatile bio-based tyramine: a case study of tyramine-derived phthalonitrile resin

Tyramine was first introduced into high-performance polymers as a promising monomer platform; the derived phthalonitrile resin exhibits excellent thermal stability and a high T_g value.

Polymerization mechanism of 4-APN and a new catalyst for phthalonitrile resin polymerization

The widely used catalysts for phthalonitrile (PN) resin polymerization are aromatic compounds containing -NH₂ because of their high catalytic performances. However, the catalytic mechanisms of these catalysts are not very clear. To understand the mechanisms of them, the widely used autocatalytic catalyst 4-(4-aminophenoxy)-phthalonitrile (4-APN) was studied in this paper. The polymerization process of 4-APN was tracked by a multi-purpose method, and ammonia gas was detected during the cross-linking processing for the fist time. Combined with the online IR results of the curing process of 4-APN, the mechanism of ammonia generation was newly proposed. Based on this mechanism, a new catalyst selection strategy was promoted, which is different from the traditional approach to catalyst selection for PN resin polymerization. According to the new strategy, 1,3-diiminoisoindoline (1,3-DII) was selected as a novel catalyst. The results showed that the new catalyst could not only effectively catalyze the polymerization of PN resin, but also has a lower curing temperature than that of organic amine catalysts and can eliminate the release of ammonia gas and the voids in the products caused thereby. Therefore, the results of this study will give important enlightenment to the development of PN catalysts and the development of PN.

Star-shaped arylacetylene resins derived from silicon

Star-shaped arylacetylene resins, tris(3-ethynyl-phenylethynyl)methylsilane, tris(3-ethynyl-phenylethynyl) phenylsilane, and tris (3-ethynyl-phenylethynyl) silane (TEPHS), were synthesized through Grignard reaction between 1,3-diethynylbenzene and three types of trichlorinated silanes. The chemical structures and properties of the resins were characterized by means of nuclear magnetic resonance, fourier-transform infrared spectroscopy, Haake torque rheomoter, differential scanning calorimetry, dynamic mechanical analysis, mechanical test, and thermogravimetric analysis. The results show that the melt viscosity at 120 °C is lower than 150 mPa⋅s, and the processing windows are as wide as 60 °C for the resins. The resins cure at the temperature as low as 150 °C. The good processabilities make the resins to be suitable for resin transfer molding. The cured resins exhibit high flexural modulus and excellent heat-resistance. The flexural modulus of the cured TEPHS at room temperature arrives at as high as 10.9 GPa. Its temperature of 5% weight loss (T d5) is up to 697 °C in nitrogen. The resins show the potential for application in fiber-reinforced composites as high-performance resin in the field of aviation and aerospace.

Novolac/Phenol-Containing Phthalonitrile Blends: Curing Characteristics and Composite Mechanical Properties

The phenol-containing phthalonitrile resin is a kind of self-curing phthalonitrile resin with high-temperature resistance and excellent properties. However, the onefold phthalonitrile resin is unattainable to cured completely, and the brittleness of the cured product is non-negligible. This paper focuses on solving the above problems by blending novolac resin into phenol-containing phthalonitrile. Under the action of abundant hydroxyl group, the initial curing temperature and gelation time at 170 °C decrease by 88 °C and 2820 s, respectively, monitored by DSC and rheological analysis. FT-IR spectra of copolymers showed that the addition of novolac increased the conversion rate of nitrile. When the novolac mass fraction is 10%, the peak of nitrile group disappears, which means the complete reaction. The mechanical test of blends composites shows that the maximum fracture strain of 10 wt% novolac addition is 122% higher than those of neat phthalonitrile composites on account of the introduction of flexible novolac chain segments. The mechanical properties are sensitive to elevated post-cured temperature; this is consistent with the result of morphological investigation using SEM. Finally, the dynamic mechanical analysis indicated that the glass transition temperature heightened with the increase of novolac content and post-curing temperature.

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.

Self-curing triphenol A-based phthalonitrile resin precursor acts as a flexibilizer and curing agent for phthalonitrile resin

Major problems currently limiting the widespread application of phthalonitrile resins are the high precursor melting point and volatility of the curing agent. Herein, a novel self-curing triphenol A-based phthalonitrile resin precursor (TPPA-Ph) was successfully synthesized by reacting α,α,α'-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene (TPPA) with 4-nitrophthalonitrile (NPh) via nucleophilic substitution. The presence of residual phenolic hydroxyl groups in the TPPA-Ph precursor promoted the curing reaction of phthalonitrile resin in the absence of an additional curing reagent. Self-cured TPPA-Ph resins exhibited relatively low melting points (less than 100 °C), high thermal stability, and a wide processing window (116 °C). Furthermore, the TPPA-Ph precursors contained phenolic hydroxyl and cyano groups that can be used as flexibilizers and curing agents to optimize other phthalonitrile resins. Resorcinol-based phthalonitrile resin (DPPH) cured with various amounts of TPPA-Ph possessed excellent thermal and thermo-oxidative stability with a 5% weight loss temperature exceeding 530 °C, T _gs above 380 °C, and a wide processing window and time. Therefore, as a novel precursor and curing agent for phthalonitrile resins, the triphenol A-based phthalonitrile resin is an ideal resin matrix for high-performance composites with broad application prospects in aerospace, shipping, machinery, and other high-tech fields.

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.

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.

A new resin with improved processability and thermal stability

To maintain outstanding thermal stability, amino- and hydroxyl-containing phthalonitrile monomers, 4-(4-aminophenoxy)-phthalonitrile (APN) and 4-(4-hydroxyphenoxy)-phthalonitrile (HPN) were selected and synthesized. Their structures were confirmed by proton nuclear magnetic resonance spectroscopy. Their curing polymers were characterized by Fourier transform infrared spectroscopy. The self-catalytic curing behaviors of the monomers were investigated by differential scanning calorimetry (DSC) at different heating rates. From the results, APN exhibits a higher curing temperature, while HPN exhibits a longer curing time. Then, mixtures of these monomers were investigated by DSC. The result shows that the 50/50 mixture exhibits different autocatalytic behaviors: the curing temperature is lower than that of APN and the curing time of the mixture is shorter than that of HPN. Furthermore, thermogravimetric analysis shows that the polymer from the mixture exhibits higher temperature of 5% weight loss ( T5%) and char yield value at 800°C than those of the polymers from each monomer. All these results indicate that the new mixture resin exhibits improved processability with excellent thermal stability, attributed to the synergistic effect between similar monomers; the synergistic effect optimizes the cure reaction kinetics and promotes cross-linking reactions, thereby producing an excellent resin; this approach is a new method for improving the processability without sacrificing thermal stability.

Synthesis and thermal properties of high temperature phthalonitrile resins cured with self-catalytic amino-contanining phthalonitrle compounds

A series of self-catalytic phthalonitrile compounds with o-, m-, and p- amino groups, namely, 4-(2-aminophenoxy)phthalonitrile (2-NH2-CN), 4-(3-aminophenoxy)phthalonitrile (3-NH2-CN), and 4-(4-aminophenoxy)phthalonitrile (4-NH2-CN), were synthesized via a facile nucleophilic displacement of a nitro-substituent with 4-nitrophthalonitrile. The phthalonitrile resins were prepared by curing 2-NH2-CN, 3-NH2-CN, and 4-NH2-CN with 1,3-bis(3,4-dicyanophenoxy) benzene ( m-BDB). The structures of these compounds were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and wide-angle X-ray diffraction. Curing behaviors of 2-NH2-CN, 3-NH2-CN, and 4-NH2-CN with m-BDB were recorded by differential scanning calorimetry. The results show that the processabilities of m-BDB with 4-NH2-CN are superior to those with 2-NH2-CN and 3-NH2-CN due to higher self-catalytic efficiency and broader processing windows. Thermal stabilities were evaluated by thermogravimetric analysis, and the polymers with all these self-catalytic compounds exhibit excellent thermal and thermal-oxidative stabilities. Dynamic mechanical analysis reveals that these polymers have high storage modulus and high glass transition temperatures. The polymers of 4-NH2-CN show more outstanding processability, thermal stability, and dynamic mechanical properties than those of 2-NH2-CN and 3-NH2-CN and can be considered as a good candidate as a self-catalytic curing agent for high-temperature phthalonitrile polymers.

A novel phthalonitrile monomer with low post cure temperature and short cure time

3-(2-Aminophenoxy)-phthalonitrile was designed and synthesized. Measurements show that the monomer has higher cure reactivity and can cure at lower temperatures in a short time and with a higher conversion, giving a better thermal stability.

Synthesis and properties of high temperature phthalonitrile polymers based on o, m, p-dihydroxybenzene isomers

o-BDB, m-BDB and p-BDB monomers with imperfect crystal structures were synthesized by a nucleophilic substitution reaction.

Temperature for curing phthalonitrile-terminated poly(phthalazinone ether nitrile) reduced by a mixed curing agent and its curing behavior

Introduction of AMTU as a curing agent into PPEN-Ph resulted in considerable reduction of the curing temperature without compromise in thermal properties.

Phthalonitrile resin bearing cyanate ester groups: synthesis and characterization

Cyanato–phthalonitrile thermosets formed by independent curing of the two groups showed increased processability but marginally reduced water repellency and thermal stability.

A curing system of benzoxazine with amine: reactivity, reaction mechanism and material properties

In addition to providing an acceleration effect on curing, suitable amines react with benzoxazine to form desired structures and improve the materials properties of the cured resins.

Self-promoted phthalimide-containing phthalonitrile resins with sluggish curing process and excellent thermal stability

A novel unsymmetrical phthalimide-containing phthalonitrile was synthesized and showed excellent thermal properties. A nucleophilic addition mechanism was introduced to explain the different reactivities of active H-containing heterocyclic structures toward phthalonitrile.

Preparation of self-promoted hydroxy-containing phthalonitrile resins by an in situ reaction

The in situ reaction of a hydroxy group with a phthalonitrile system was carried out in a one-pot reaction and the prepared polymers showed outstanding thermal stability, a high modulus and a high glass transition temperature.

Thermally stable phthalonitrile resins based on multiple oligo (aryl ether)s with phenyl-s-triazine moieties in backbones

Phenyl-s-triazine segments in the polymer backbones endowed phthalonitrile networks with enhanced thermal stability, which could also be tuned by the main-chain lengths of the aromatic ether.