Phthalonitrile terminated fluorene based copolymer with outstanding thermal and mechanical properties

Synthesis of oligomeric phthalonitrile resins containing imide units and study of the methylene-cyano thermal synergistic polymerization effect

The meta- and para-catenated methylene-containing phthalonitrile oligomers were prepared from the reaction of an excess amount of 4,4′-(4,4′-isopropylidenediphenoxy) bis-(phthalic anhydride) (BPADA) with 4,4′-Methylenedianiline (MDA) in a N, N-dimethylformamide/ toluene solvent mixture, followed by end-capping agent with 4-nitrophthalonitrile or 4-phenoxyaniline in a two-step, one-pot reaction. Differential scanning calorimetry (DSC) showed that both PN oligomers exhibited low softening points. The self-catalyzed curing reactivity of the PN oligomers was confirmed by the isothermal rheological measurements. Fourier transform infrared spectroscopy (FTIR) and ultraviolet and visible spectrophotometry (UV–Vis) data of the pre-curing resins were employed to investigate the chemical structure of the pre-cured resins, suggesting that oligomers generated crosslinking sites, including triazine, isoindoline, and phthalocyanine. The results further confirmed the self-catalyzed curing reactivity of the oligomers. Thermal properties were investigated by dynamic mechanical analysis (DMA) and thermal gravimetric analysis (TGA), demonstrating good thermal properties of the cured resins. The glass transition temperatures (Tgs) of PIPN-1-325, PIPN-1-350, PIPN-1-375 were in the range of 285–345°C, the 5% weight loss temperature (T5%) was observed at 482°C. The PIPN-2-325, PIPN-2-350, PIPN-2-375 showed Tgs ranging from 293 to 370°C, and T5% of the resins were in the range of 481–501°C. Then the isothermal rheological results of model compound and PN oligomers implied that the curing process of PN oligomers was closely related to the methylene-cyano radical thermal synergistic polymerization (TSP) effect proposed in our previous research, and then a revised curing mechanism (radical TSP mechanism) was proposed.

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.

Preparation and characterization of phthalonitrile resin within hyperbranched structure

In this article, a kind of polyester-type phthalonitrile cyano resin (2,2-bis (((3-((4-(3,4-dicyanophenoxy) benzoyl)oxy)-2-(hydroxymethyl)-2-methylpropanoyl)oxy)methyl) propane-1,3-diyl)bis(oxy)) bis (2-(hydroxymethyl)-2-methyl-3-oxopropane-3, 1-diyl) bis (4-(3,4-dicyanophenoxy) benzoate (hbppn)) with branched structure was introduced. The molecular structure and relative molecular mass of hbppn were characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF). The results showed that the synthesized HBPPN contained both polyester and hyperbranched structures. The thermal and rheological properties of HBPPN were characterized by differential scanning calorimetry and rheometer, and the results showed that HBPPN would be cured at about 322°C and the viscosity of the resin showed good processability. The results of dynamic mechanical analysis and thermogravimetric analysis showed that the synthesized resin had good heat resistance. The glass transition temperature was above 329°C, the residual weight ( C y) at 900°C was as high as 66.2% in the nitrogen atmosphere, and the temperature at which the resin lost 5 wt% of heat in air atmosphere was about 423.3°C. The synthesized HBPPN had good comprehensive properties, which could be applied to high-temperature resistant and thermal protection materials.

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.