Syntheses and Crystal Structures of Some Aryloxy and Alkoxy Substituted Phthalonitriles

Phthalonitriles substituted with aryloxy and alkoxy groups have been synthesized and characterized by elemental analyses, IR, mass spectra and IH NMR spectroscopy. And four of such crystal structures have also been determined. In the crystal structures, the major intermolecular interactions between the neighboring molecules are the hydrogen bonds as C-N…H and C=O…H that lead to similar networks in the crystal structures.

Synthesis and Crystal Structure of 4,5-Bis(2-chloroethylthio)phthalonitrile

A novel phthalonitrile compound,[C12H10Cl2N2S2],has been synthesized and its crystal structure was determined by single-crystal X-ray diffraction.The crystal belongs to the monoclinic system,space group P21/n with a = 10.6417（8）,b = 7.5737（6）,c = 18.2758（14）,β = 105.2480（10）°,Mr = 317.24,V = 1421.12（19）3,Z = 4,Dc = 1.483 g/cm3,F（000） = 648,μ = 0.733 mm-1,R = 0.0173 and wR = 0.2183.In the structure,the C atoms of the aromatic ring,the two cyanide groups and the two S atoms are almost coplanar（maximum deviation from the mean plane = 0.049（7） ）.Two potential weak intermolecular interactions of C-H…N and one type of π…π stacking interaction with a centroid-centroid separation of 3.751（8） stabilize the crystal structure.

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 biobased monomers could be cured without the addition of catalysts, and improvement in processability was achieved at no cost of thermal performances.

Insights into Phthalonitrile/Epoxy Blends Modification System from Non-competitive Cure System Based on Alicyclic Anhydride

A series of polymer blends were prepared from 1,3-bis（3,4-dicyanophenoxy）benzene（3 BOCN） and epoxy resin with methyl tetrahydrophthalic anhydride as curing agent. The curing behavior and curing kinetics of the blends were studied by differential scanning calorimetry. The apparent activation energy of the blends with various contents of 3 BOCN was higher than that of the blends without 3 BOCN. A model experiment suggested that there is no obvious reaction between phthalonitrile and epoxy. The thermal and mechanical properties of the polymer blends were evaluated. The polymer blends exhibit high storage modulus and char yield compared with the neat epoxy. The polymer blends show ductile fracture morphology by scanning electron microscopy（SEM） images.

Designing a Phthalonitrile/Benzoxazine Blend for the Advanced GFRP Composite Materials

High performance resin must be used in the high performance glass fiber-reinforced plastic（GFRP） composites, but it is sometimes difficult to balance the processabilities and the final properties in the design of advanced thermoset GFRP composites. In this study, a phthalonitrile/benzoxazine（PPN/BZ） blend with excellent processability has been designed and applied in the GFRP composite materials. PPN/BZ blend with good solubility, low melt viscosity, appropriate gel condition and low-temperature curing behavior could enable their GFRP composite preparation with the prepreg-laminate method under a relatively mild condition. The resulted PPN/BZ GFRP composites exhibit excellent mechanical properties with flexural strength over 700 MPa and flexural modulus more than 19 GPa. Fracture surface morphologies of the PPN/BZ GFRP composites show that the interfacial adhesion between resin and GF is improved. The temperatures at weight loss 5%（T_（5%）） and char residue at 800 °C of all PPN/BZ GFRP composites are over 435 °C and 65% respectively. PPN/BZ GFRP composites with high performance characteristics may find applications under some critical circumstances with requirements of high mechanical properties and high service temperatures.

Multiple-SO3H functioned ionic liquid as efficient curing agent for phthalonitrile-terminated poly(phthalazinone ether nitrile)

Combined with the advantages of low melting point,high thermal stability and strong acidity,a multipleSO_3H functioned ionic liquid（MIL） was developed successfully as a curing agent to promote the curing reaction of phthalonitrile-terminated poly（phthalazinone ether nitrile）（PPEN-Ph）.The curing kinetics over differential scanning calorimetry（DSC） showed that both the initial curing temperature Tp0＇ and apparent activation energy Ea＇（based on Kissinger equation） were reduced significantly over MIL（207.9℃ and 101.5 kJ/mol） compared to the common curing agent ZnCl_2（268.5℃ and 201.5 kJ/mol）.Moreover,under identical curing conditions,the resulting thermosetting resin over former（Td5%=526.1℃） showed better thermal stability than that over latter（Td5%=512.1 ℃）.These results indicated that MIL should be a good candidate as a curing agent for phthalonitrile resins.

Phenyl-triggered photophysical switching between normal fluorescence and delayed fluorescence in phthalonitrile-based luminophores

Herein,a facile strategy for switching luminescent properties between normal fluorescence and thermally activated delayed fluorescence(TADF)is presented.Two luminophoric molecules,VPN-Ph and VPN-H,combining phthalonitrile as an electron-accepting core and triphenylamines as electron-donating peripheries with and without two phenyl groups,are newly developed.A comparative study on their structural and photophysical properties is conducted.While non-phenyl VPN-H does not exhibit TADF but normal fluorescence,phenyl-introduced VPNPh exhibits TADF with a high photoluminescence quantum yield as a consequence of the phenyl-triggered steric congestion.By virtue of the TADF feature,an organic light-emitting diode(OLED)incorporating VPN-Ph as an emitter achieves a maximum external electroluminescence(EL)quantum efficiency as high as 28.0%,which is five times higher than that of the VPN-H-based OLED.Thus,phenyl-triggered geometric modulation has a drastic impact on the resulting photophysical and EL properties,leading to TADF on/off switching.

Boron-containing Phthalonitrile Resin:Synthesis,Curing Behavior,and Thermal Properties

A novel boron-containing monomer,(4-(3,4-dicyanophenoxy)phenyl)boronic acid(BPhPN)was synthesized and used to promote the curing process of phthalonitrile monomer 1,3-bis(3,4-dicyanophenoxy)benzene(MPN).Differential scanning calorimetry and rheological analysis were used to study the curing behaviors of BPhPN/MPN(namely B-MPN),and results suggested that B-MPN systems have better processibility.FTIR spectra and solid-state 13C-NMR exhibited triazine and isoindoline have been formed in the curing process.Boron-containing Lewis acid curing mechanism was preliminarily speculated and verified by two model compounds with different boron chemical environments.The thermogravimetric analysis and dynamic mechanical analysis demonstrated that the cured B-MPN polymers showed excellent thermal stability and heat resistance,which were comparable with conventional catalytic systems for phthalonitrile resins.This study not only presented a novel curing system for phthalonitrile resins,but also shed light on future design of high temperature thermosets.

Phthalonitrile-PPO Blends: Cure Behavior and Properties

Hydroxy-containing low molecular weight poly（2,6-dimethyl-1,4-phenylene oxide）（r PPO） and self-promoted hydroxycontaining phthalonitrile（HPPH） were prepared by redistribution reaction and the simple nucleophilic displacement of a nitro-substituent from 4-nitrophthalonitrile in a dipolar aprotic solvent respectively. The hydroxy-containing phthalonitriles modified by r PPO were prepared by mechanical blending without compatibilizer, followed by heating. The curing behavior was studied using dynamic rheological analysis, and the results showed that the r PPO-modified phthalonitrile exhibited a large processing window（over-67 °C） and complex viscosity（0.18-0.8 Pa·s） at moderate temperatures. After curing at 300 °C, the resulting polymers showed good thermal stability and high modulus as observed by thermogravimetric analysis（TGA） and dynamic mechanical analysis（DMA）. The dielectric properties and the morphology of r PPO-modified phthalonitrile networks were studied by dielectric analysis and field-emission scanning electron microscopy（SEM）.

Synthesis of a novel naphthyl-based self-catalyzed phthalonitrile polymer

A novel naphthyl-based self-catalyzed phthalonitrile monomer was prepared via nucleophilic displacement reaction. The structure was characterized by Fourier infrared spectrum （FT-IR） and nuclear magnetic resonance （^1H NMR）. The polymerization mechanism was explored. Thermal properties were characterized by differential scanning calorimetry （DSC） and thermogravimetric analysis （TGA）, which demonstrated self-promoted behavior and excellent heat resistance.