Phthalonitrile-Terminated Silicon-Containing Oligomers: Synthesis, Polymerization, and Properties

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.

Fast-Processable Non-Flammable Phthalonitrile-Modified Novolac/Carbon and Glass Fiber Composites

Phthalonitrile resins (PN) are known for their incredible heat resistance and at the same time poor processability. Common curing cycle of the PN includes dozens hours of heating at temperatures up to 375 °C. This work was aimed at reducing processing time of phthalonitrile resin, and with this purpose, a novolac oligomer with hydroxyl groups fully substituted by phthalonitrile moieties was synthesized with a quantitative yield. Formation of the reaction byproducts was investigated depending on the synthesis conditions. The product was characterized by ¹H NMR and FT-IR. Curing of the resins with the addition of different amounts of novolac phenolic as curing agent (25, 50 and 75 wt.%) was studied by rheological and DSC experiments. Based on these data, a curing program was developed for the further thermosets' investigation: hot-pressing at 220 °C and 1.7 MPa for 20 min. TGA showed the highest thermal stability of the resin with 25 wt.% of novolac (T_5% = 430 °C). The post-curing program was developed by the use of DMA with different heating rates and holding for various times at 280 or 300 °C (heating rate 0.5 °C/min). Carbon and glass fiber plastic laminates were fabricated via hot-pressing of prepregs with T_g's above 300 °C. Microcracks were formed in the CFRP, but void-free GFRP were fabricated and demonstrated superior mechanical properties (ILSS up to 86 MPa; compressive strength up to 620 MPa; flexural strength up to 946 MPa). Finally, flammability tests showed that the composite was extinguished in less than 5 s after the flame source was removed, so the material can be classified as V-0 according to the UL94 ratings. For the first time, fast-curing phthalonitrile prepregs were presented. The hot-pressing cycle of 20 min with 150 min free-standing post-curing yielded composites with the unique properties. The combination of mechanical properties, scale-up suitable fast-processing and inflammability makes the presented materials prospective for applications in the electric vehicle industries, fast train construction and the aerospace industry.

Rational Design of Fluorinated Phthalonitrile/Hollow Glass Microsphere Composite with Low Dielectric Constant and Excellent Heat Resistance for Microelectronic Packaging

High-performance composites with a resin matrix are urgently required for electronic packaging due to their low dielectric constant, outstanding high temperature resistance, excellent corrosion resistance, light weight and easy molding. In this work, hollow-glass-microsphere (HGM)-filled fluorinated-phthalonitrile (PBDP) composites, with filler contents ranging from 0 to 35.0 vol.%, were prepared in order to modify the dielectric properties of the phthalonitrile. Scanning electron microscopy (SEM) observations indicate that the modified HGM particles were uniformly dispersed in the matrix. The PBDP/27.5HGM-NH₂ composite demonstrates a low dielectric constant of 1.85 at 12 GHz. The 5% thermogravimetric temperature (T₅) of composites with silanized HGM filler (481-486 °C) is higher than the minimum packaging-material requirements (450 °C). In addition, the heat-resistance index (T_HRI) of PBDP/HGM-NH₂ composites reached as high as 268 °C. the storage modulus of PBDP/HGM-NH₂ composites were significantly increased to 1283 MPa at 400 °C, an increase by 50%, in comparison to that of PBDP phthalonitrile resin (857 MPa). The excellent dielectric and thermal properties of the present composites may pave a way for comprehensive applications in electronic packaging and thermal management for energy systems.

Synthesis of Pyridine Heterocyclic Low-Melting-Point Phthalonitrile Monomer and the Effects of Different Curing Agents on Resin Properties

A phthalonitrile monomer (DPTP) containing pyridine with sulfide bonds was prepared and cured into polymers using different curing agents under the same temperature-programmed process. We characterized and comprehensively evaluated the effects of different curing agents on the thermal and thermomechanical properties of phthalonitrile resin, showing that the DPTP monomer cured with naphthalene-containing curing agent exhibited the best performance among the three polymers. Differential scanning calorimetric (DSC) investigation manifested that the melting point of the DPTP monomer was 61 °C, with a processing window of about 170 °C, suggesting the presence of a wide processing range. Thermogravimetric analysis (TGA) demonstrated the outstanding heat resistance, T5%, of 460 °C in nitrogen, at the same time demonstrating superior long-term stability compared with other commonly used polymer materials, which proves the long-term usage under high temperatures of 300 °C. Dynamic mechanical analysis (DMA) revealed that the storage modulus at 50 °C was 3315 MPa, and the glass transition temperature (Tg) of the polymer was more than 350 °C. Therefore, DPTP resins have favorable thermal stability as well as prominent thermomechanical properties.

A Pyridazine-Containing Phthalonitrile Resin for Heat-Resistant and Flame-Retardant Polymer Materials

In this study, a novel phthalonitrile monomer containing a pyridazine ring, 3,6-bis[3-(3,4-dicyanophenoxy)phenoxy]pyridazine (BCPD) with a low melting point (74 °C) and wide processing window (178 °C), was prepared by a nucleophilic substitution reaction. The molecular structure of the BCPD monomer was identified by Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). Poly(BCPD) resins were derived from the formulations by curing at 350 and 370 °C. The thermoset that was post-cured at 370 °C demonstrated outstanding high heat-resistant (glass transition temperature (Tg) > 400 °C, 5% weight loss temperature (T5%) = 501 °C, Yc at 900 °C > 74%) and was flame-retardant (limiting oxygen index (LOI) = 48)). Further, the poly(BCPD) resin simultaneously exhibited a superior storage modulus, which could reach up to 3.8 Gpa at room temperature. Excellent processability and heat resistance were found for phthalonitrile thermosets containing the pyridazine ring, indicating poly(BCPD) resin could be potentially applied as high-temperature structural composite matrices.

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.

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.

A high-performance functional phthalonitrile resin with a low melting point and a low dielectric constant

A monomer of fluorinated phthalonitrile, namely 4,4'-bis(p-perfluoro-phenol-(bis(p-phenol)propane-2,2-diyl)-p-oxy-diphthalonitrile) (PBDP), was synthesized by the nucleophilic substitution reaction of bisphenol A, decafluorobiphenyl and 4-nitrophthalonitrile. The structure of the monomer was characterized by nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The results indicated that the PBDP monomer was synthesized successfully. The monomer was cured in the presence of 4-(aminophenoxy)phthalonitrile (APPH) and the curing behaviour was investigated by differential scanning calorimetry (DSC), suggesting a low melting point of 96 °C and an excellent processing window (96-262 °C). Thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) showed that the fluorinated phthalonitrile resin possessed outstanding thermal and thermo-oxidative stabilities as well as good mechanical properties. The glass transition temperature was >400 °C and the 5% thermal degradation temperature was 501 °C. When the frequency was 50 MHz, the dielectric constant and dielectric loss of the polymer were 2.84 and 0.007, respectively. The PBDP resin has ultra-low water absorption of 0.77% and 1.4%, when exposed to an aqueous environment for 50 days at 24 °C and for 24 h at 100 °C, respectively. The prepared PBDP resin with outstanding thermal stability and low dielectric constant is an ideal candidate for aerospace industries, and microelectronic and other electronic packaging materials.