Octakis(ethynyldimethylsiloxy)silsesquioxane (OEMS) was first synthesized via hydrolysis condensation reaction between tetramethylammonium octaanion and ethynyldimethylchlorosilane, and characterized by FT-IR, NMR, and GPC methods. A series of OEMS modified poly(silicane arylacetylene) resins (OEMS-PSAs) were prepared from OEMS and poly(silicane arylacetylene) (PSA). TEM analysis of the OEMS-PSAs confirms that the nano-sized polyhedral oligomeric silsesquioxanes (POSS) are dispersed evenly in low content, but aggregated unregularly in high content in OEMS-PSAs. The curing behavior of OEMS-PSAs was studied with DSC and FT-IR techniques. Nanoindentation test shows the incorporation of OEMS into PSA could decrease both of the elastic modulus and surface hardness of the PSA thermoset. The dielectric constants (E r ) of the OEMS-PSA thermosets approach to 2.1, depending on not only the content of POSS but also the dispersion of POSS. Furthermore, TGA results demonstrate the OEMS-PSA thermosets possess the certain thermo-oxidative resistance.

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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.

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