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.
Highlights
As one of the densely cross-linked networks of organic repeat units, phthalonitrile resin provides tunable desired properties through a flexible synthetic [1]
Cyanide polymerization can be effectively facilitated by the hydroxyl/amino groups produced during the curing process of the blend resins
The melting point of Biphenyl phthalonitrile (BPh) monomer is up to 237 ◦C, which is difficult for the dry prepreg process and melt technologies to meet
Summary
As one of the densely cross-linked networks of organic repeat units, phthalonitrile resin provides tunable desired properties through a flexible synthetic [1]. The instability and low melting point of the small molecule curing additives may cause the voids within the phthalonitrile thermoset and decrease its heat resistance [11,12]. To solve this problem, self-polymerizing phthalonitrile resin was considered [1,13,14]. Cyanide polymerization can be effectively facilitated by the hydroxyl/amino groups produced during the curing process of the blend resins. The temperature resistance of these resins is great, it is difficult to further improve the thermal stability of phthalonitrile resin by blending with them. It was not easy to obtain both accelerated curing process and improved heat resistance performance
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