Zhihuan Weng

Promoting and Tuning Porosity of Flexible Ether-Linked Phthalazinone-Based Covalent Triazine Frameworks Utilizing Substitution Effect for Effective CO2 Capture

Five porous ether-linked phthalazinone-based covalent triazine frameworks (PHCTFs) were successfully constructed via ionothermal polymerizations from flexible dicyano monomers containing asymmetric, twisted, and N-heterocyclic phthalazinone structure. All the building blocks could be easily prepared by simple and low-cost aromatic nucleophilic substitution reactions, showing the large-scale application potential of thermal stable phthalazinone structure in constructing porous materials. Generally, the flexible building blocks are avoided to prevent the networks from collapsing in constructing high surface area porous materials. Our experimental results revealed that the introduction of the substituents can effectively decrease the probability of the network interpenetration from the longer struts and the intermolecular/intramolecular intercalation from the increased degree of conformation freedom in the flexible ether-linkage, the BET surface areas of PHCTFs increasing from 676 to 1270 m2 g-1. Meanwhile, the effects of introducing different sizes (methyl or phenyl group) and amounts (one or two) of substituents on the porosities of the target polymer networks were also investigated in detail. The high CO2 adsorption capacity of 10.3 wt % (273 K, 1 bar) can be ascribed to the strong affinity of the electron-rich N,O-containing networks with CO2. Excitingly, PHCTF-5 demonstrates the high CO2/N2 selectivity up to 138 (273 K, 1 bar), according to the ideal adsorbed solution theory (IAST) for the higher proportion of Vmicro accompanied the electron-rich heteroatoms characteristic. Such high CO2 adsorption capacity and good separation properties are superior to those of many other microporous organic polymers. These properties along with easily up-scalable synthesis make porous PHCTFs promising candidates applied in gas sorption and separation field.

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

A mixture of ammonium molybdate tetrahydrate and urea (AMTU) was developed successfully to catalyze phthalonitrile to afford 2,4,6-tris(2-cyanophenyl)-1,3,5-triazine. Then AMTU was employed as a curing agent to promote the curing reaction of phthalonitrile-terminated poly(phthalazinone ether nitrile) (PPEN-Ph), and the effect of the novel curing agent was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The initial curing temperature and apparent activation energy Ea (based on the Kissinger equation) were reduced from 268.5 °C and 201.5 kJ mol−1 using the common curing agent ZnCl2, to 223.0 °C and 78.4 kJ mol−1 using AMTU, respectively, under identical curing conditions. Moreover, the resulting thermosetting resin over AMTU showed excellent thermal stability; the Td5% and Td10% were 487 °C and 540 °C, respectively, and the char residue was up to 75% at 800 °C. These results indicated that AMTU could reduce the curing temperature for PPEN-Ph effectively, and it may be a good candidate as a curing agent for phthalonitrile resins.

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, Tgs 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.

Preparation of Novel Epoxy Resins Bearing Phthalazinone Moiety and Their Application as High-Temperature Adhesives

Most polymer-based adhesives exhibit some degree of degradation at temperatures above 200 °C, and so there is a need for the development of adhesives that can be used at high temperatures. A series of poly(phthalazinone ether nitrile sulfone ketone)s terminated with epoxy (E-PPENSK) and amine (A-PPENSK) groups have been prepared, which have been used as precursors can be applied for high-temperature resistant epoxy adhesives. The structured of these E-PPENSK (epoxy resin) and A-PPENSK (curing agent) components have been characterized by 1H nuclear magnetic resonance (NMR) and Fourier transform–infrared spectroscopy (FT–IR) studies, with the effects of molecular weights and molar ratios on the gel content of their polymers being determined. Cured epoxy resins derived from E-PPENSK and A-PPENSK showed good thermal stability, with an optimal resin retaining 95% of its weight at 484 °C, which gave a char yield of 62%. This adhesive was found to exhibit good mechanical strength, with a single-lap adhesive joint (A-3000/E-6000) exhibiting a shear strength of 48.7 MPa. Heating this adhesive at 450 °C for 1 h afforded a polymer that still exhibited good shear strength of 17.8 MPa, indicating that these adhesives are potentially good candidates for high-temperature applications.

Construction of flexible and stable near-infrared absorbing polymer films containing nickel-bis(dithiolene) moieties via ligand-exchange post-polymerization modification

Flexible and stable near-infrared (NIR) absorbing polymer films were prepared from the corresponding poly(aryl ether) precursors through subsequent ligand-exchange post-polymerization modification. The additional ligand triggers the ligand-exchange reaction during the post-polymerization modification process, which can significantly enhance the polymer yield, as well as the coordination ratio of the nickel-bis(dithiolene) segment in the polymer backbone by suppressing cross-linking side reactions. The presented ligand-exchange post-polymerization modification overcomes the limitations of the post-polymerization modification reaction, i.e. a high degree of cross-linking between the same reactive groups, and enhances the modification methods of analogous polymers. Upon incorporating the nickel-bis(dithiolene) moiety into the polymer backbone, the resulting polymers exhibit both strong near-infrared absorption at approximately 1200 nm with e > 104 mol−1 L cm−1 in an NMP solution and excellent free-standing film formation properties. The long-term aging-resistance test indicates that the incorporation of the nickel-bis(dithiolene) moiety into the polymer chain via chemical bonding is superior to physical blending for stabilizing the nickel-bis(dithiolene) moiety. Although the absorbance of the micromolecular NIR dyes Ni–O and Ni–N at the maximum wavelength gradually decreased up to 34% during the aging test (70 °C for 144 h), it should be noted that the NiO-P6 (10 mol% nickel-bis(dithiolene) segments) and NiN-P8 (34 mol% nickel-bis(dithiolene) segments) polymer films exhibited no decrease in the NIR absorption range. Finally, this work shows that the post-polymerization modification between the same reactive groups could also be an effective approach to install functional groups in a polymer backbone while avoiding a high degree of cross-linking side reactions, as well as offers an approach to design near-infrared absorbing polymeric materials with balanced near-infrared absorption and solution-processing properties.