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.
In order to improve the heat‐resistance of poly(arylene ether nitriles) (PEN), a novel mono‐cyano crosslinking strategy—heat‐induced synergistic polymerization of aromatic methylene and mono‐cyano is proposed and applied in the PEN system. A self‐crosslinkable PEN containing aromatic methylene moieties (PEN‐F) is synthesized by a simple solution polycondensation. PEN‐F can significantly crosslink during relatively mild heat treatment at 300–325°C without any catalyst, transferring from thermoplastic polymers to thermosetting polymers. XRD, FTIR, TGA, DSC and DMA are applied to evaluate the crystallinity, structural evolution and thermal properties of PEN‐F before and after crosslinking. The results suggest that the uncured PEN‐F is amorphous and soluble in some common solvents (THF, DMAc, NMP, etc.). After curing, the heat and solvent resistance of PEN‐F improve remarkably. Especially, the resulting crosslinked product PEN‐F‐325 exhibits a high glass transition temperature (Tg) value of 320°C measured by DMA, increased by 148°C compared to uncured PEN‐F (Tg = 172°C), potentially applicable for high temperature services.
Developing high-performance polymer (HPP) with improved properties by green processing method is one of the core parts of HPP research. In this paper, a new monomer (4,4 0 -((propane-2,2-diylbis(4,1-phenylene))bis(oxy)) dibenzaldehyde (PBhDCI)) of high-performance aromatic nitrile-based (AN) resins with good solubility in ethanol was designed. The rheological analysis showed that PBhDCI is suitable for the processing by laminating process.The cured resins and the corresponding carbon fiber reinforced plastics (CFRP) showed outstanding thermal and mechanical properties. The thermal decomposition temperature (T 5% ) of the cured PBhDCI under nitrogen up to 510 C, the glass transition temperature (T g ) of both resin matrix and CFRP exceeds 500 C, and the flexural strength and modulus of CFRP were 507 ± 5 MPa and 59 ± 2 GPa. This work will offer some guidance for the preparation of high-performance resins and corresponding CFRP with a green processing and high thermal and mechanical properties.
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