A novel hyperbranched poly(phenylene oxide) (HBPPO) modified 2,2 0 -bis(4-cyanatophenyl) isopropylidene (BCE) resin system with significantly reduced curing temperature and outstanding dielectric properties was developed, and the effect of the content of HBPPO on the curing behavior and dielectric properties as well as their origins was thoroughly investigated. Results show that BCE/HBPPO has significantly lower curing temperature than BCE owing to the different curing mechanisms between the two systems, the difference also brings different crosslinked networks and thus dielectric properties. The dielectric properties are frequency and temperature dependence, which are closely related with the content of HBPPO in the BCE/HBPPO system. BCE/2.5 HBPPO and BCE/5 HBPPO resins have lower dielectric constant than BCE resin over the whole frequency range tested, while BCE/10 HBPPO resin exhibits higher dielectric constant than BCE resin in the low frequency range (<10 4 Hz) at 200 C. At 150 C or higher temperature, the dielectric loss at the frequency lower than 10 2 Hz becomes sensitive to the content of HBPPO. These phenomena can be attributed to the molecular relaxation. Two relaxation processes (a-and b-relaxation processes) are observed. The b-relaxation process shifts toward higher frequency with the increase of temperature because of the polymer structure and chain flexibility; the a-relaxation process appears at high temperature resulting from the chain-mobility effects.

High curing temperature is the key drawback of present heat resistant thermosetting resins. A novel epoxy-functionalized hyperbranched poly(phenylene oxide), coded as eHBPPO, was synthesized, and used to modify 2,2 0 -bis (4-cyanatophenyl) isopropylidene (CE). Compared with CE, CE/eHBPPO system has significantly decreased curing temperature owing to the different curing mechanism. Based on this results, cured CE/eHBPPO resins without postcuring process, and cured CE resin postcured at 230 C were prepared, their dynamic mechanical and dielectric properties were systematically investigated. Results show that cured CE/eHBPPO resins not only have excellent stability in dielectric properties over a wide frequency range (1-10 9 Hz), but also show attractively lower dielectric constant and loss than CE resin. In addition, cured CE/eHBPPO resins also have high glass transition temperature and storage moduli in glassy state. These attractive integrated performance of CE/eHBPPO suggest a new method to develop high performance resins.

Advanced wave-transparent composites are the key materials for many cutting-edge industries including aviation and aerospace, which should have outstanding heat resistance, low dielectric constant and loss as well as good mechanical properties. A novel kind of high-performance wave-transparent composites based on surface-modified aluminum phosphate AlPO 4 (KH-550) and cyanate ester (CE) was first developed. The dielectric and dynamic mechanical properties of AlPO 4 (KH-550)/CE composites were investigated intensively. Results show that AlPO 4 (KH-550)/ CE composites have decreased dielectric loss and higher storage moduli than pure CE resin; in addition, the composites with suitable AlPO 4 (KH-550) concentration remain the outstanding thermal property and low dielectric constant of pure CE resin. The reasons attributing to these results are discussed from the effects of AlPO 4 (KH-550) on the key aspects such as morphology, curing mechanism, and interfacial adhesion of composites.

High-performance hyperbranched poly(phenylene oxide)-modified bismaleimide resin with high thermal stability, low dielectric constant, and loss was developed, which is made up of hyperbranched poly(phenylene oxide) (HBPPO), 4,4 0 -bismaleimidodiphenylmethane (BDM), and o, o 0 -diallylbisphenol A (DBA). The curing reactivity, morphology, and performance of BDM/DBA/HBPPO resin were systemically investigated, and similar investigations for BDM/ DBA resin were also carried out for comparison. Results show that BDM/DBA/HBPPO and BDM/DBA resins have similar curing mechanism, but the former can be cured at lower temperature than the later; in addition, cured BDM/ DBA/HBPPO resin with suitable HBPPO content has better thermal stability and dielectric properties (lower dielectric constant and loss) than BDM/DBA resin. The difference in macroproperties between BDM/DBA/HBPPO and BDM/ DBA resins results from the different chemical structures and morphologies of their crosslinking networks.

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