Catalytic Polymerization of Phthalonitrile Resins by Carborane with Enhanced Thermal Oxidation Resistance: Experimental and Molecular Simulation

Abstract

Biphenyl phthalonitrile (BPh) resins with good thermal and thermo-oxidative stability demonstrate great application potential in aerospace and national defense industries. However, BPh monomer has a high melting point, poor solubility, slow curing speed and high curing temperature. It is difficult to control the polymerization process to obtain the resins with high performance. Here, a BPh prepolymer (BPh-Q) was prepared by reacting 1,7-bis(hydroxymethyl)-m-carborane (QCB) with BPh monomers. The BPh-Q exhibited much better solubility, faster curing speed and lower curing temperature compared with pure BPh and BPh modified with bisphenol A (BPh-B, a common prepolymer of BPh). Thus, the polymerization process of BPh was greatly accelerated at a low temperature, resulting in a BPh resin with enhanced thermostability and oxidation resistance. The experimental and theoretical models revealed the promotion effect of B-H bond on the curing reaction of phthalonitrile via Markovnikov addition reaction due to the special steric structure of carborane. This study provided an efficient method to obtain low-temperature curing phthalonitrile resins with high thermal and thermo-oxidative resistance, which would be potentially useful for the preparation of high-performance cyanide resin-based composites.

Carborane-Containing Polymers: Synthesis, Properties, and Applications

“…For example, di-(hydroxymethyl) closo-1,7-carborane 15 was found to enhance . 87 In other cases, closo-1,2-carborane was incorporated into initiators for living polymerizations to afford polymers with a carborane cage at one end of the chain. The only carborane RAFT agent known to date was reported by Messina et al in 2019.…”

Thermal-Oxidation-Resistant Poly(Carborane-Silane) for Protective Coatings Under Harsh Environments

“…Carborane and its derivatives are highly sought after due to their 3D-aromatic structure and have been investigated to improve the heat stability of organic polymers. Carborane is soluble in commonly used organic solvents and can be easily introduced into polymer systems such as polyester, , polysiloxane, , polyamides/polyimides, − polyphosphazenes, − heteroelement-substituted polymers, , and so on. − Among the polymers discussed above, polysiloxane stands out because the introduction of carborane segments substantially improves its heat resistance. The addition of carborane segments significantly improved the modified polymers’ thermal resistance.…”

Heat-Resistant Phthalonitrile-Based Resins for 3D Printing via Vat Photopolymerization

“…Thermal polymerization of phthalonitriles requires an initiator, such as aromatic amine or phenol, occurs with formation of isonoindoline, triazine, and phthalocyanine structures, and yields thermosets with extraordinarily high heat resistance ( T g up to 450 °C and T 5% > 500 °C), which are considered to be promising matrices for composites for operation under extreme conditions. − However, to the best of our knowledge, there have been no reports of utilizing PN resins for selective photocuring via 3D printing. Phthalonitrile resins are known for poor processability due to high melting points of the monomers, as well as high curing temperatures. ,,− High crystallinity (and, as a consequence, high melting points) might lead to low solubility in different solvents while it is necessary to dissolve solid phthalonitrile monomers in photopolymerizable comonomers to perform VP. − Moreover, phthalonitrile polymerization is typically initiated with an aromatic diamine, which can potentially act as an inhibitor for free-radical polymerization, hindering VP processing . Recently, our research group has successfully designed a low-melting and self-curing phthalonitrile monomer grafted with a maleimide group 4-[3-(2,5-dione-1 H -pyrrole-1-yl)­phenoxy]­benzene-1,2-dicarbonitrile (PNB-M) .…”