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New high performance insulating composites based on hollow silica tubes (mHST) and bismaleimide/diallylbisphenol A (BDM/DBA) resin, which exhibit improved toughness, dielectric properties, and flame retardancy, were successfully developed. The effect of the amount of mHST on the properties of composites was systematically studied. Results show that the impact strength of the composite with 0.5 wt% mHST is about 2.2 times that of BDM/DBA resin. In addition, compared with BDM/DBA resin, the composites show lower and stable dielectric constant, better frequency stability of dielectric loss, significantly improved flame retardancy, and similarly outstanding thermal resistance. The reasons behind these attractive integrated properties are discussed from the view of structure-property relationship. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Novel modified cyanate ester (CE) resins with decreased dielectric loss, improved thermal stability, and flame retardancy were developed by copolymerizing CE with hyperbranched phenyl polysiloxane (HBPPSi). HBPPSi was synthesized through the hydrolysis of phenyltrimethoxysilane, and its structure was characterized by 1H-NMR, 29Si-NMR, and Fourier transform infrared spectra. The effect of the incorporation of HBPPSi into CE resin on the curing behavior, chemical structure of cured networks, and typical performance of HBPPSi/CE resins were systemically evaluated. It is found that the incorporation of HBPPSi into CE network obviously not only catalyzes the curing of CE, but also changes the chemical structure of resultant networks, and thus results in significantly decreased dielectric loss, improved thermal stability, and flame retardancy as well as water absorption resistance. For example, in the case of the modified CE resin with 10 wt% HBPPSi, its limited oxygen index is about 36.0, about 1.3 times of that of neat CE resin, its char yield at 800°C increases from 31.6 to 35.4 wt%; in addition, its dielectric loss is only about 61% of that of neat CE resin at 1 kHz. All these changes of properties are discussed from the view of the structure-property relationship. The significantly improved integrated properties of CE resin provide a great potential to be used as structural and functional materials for many cutting-edges fields. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: A novel kind of modified bismaleimide/cyanate ester (BCE) resins by copolymerizing with hyperbranched polysiloxane including high content of phenyl (HBPSi) was first reported. The effect of HBPSi on the curing mechanism, and that on the dielectric properties and flame retardancy of cured networks were systemically investigated. Results show that compared with BCE resin, HBPSi/BCE resin has obviously different cross-linked structure, and thus leading to simultaneously improved dielectric properties and flame retardancy. The reactions between HBPSi and the decomposition structure of BCE resin change the thermo-oxidative degradation mechanism of the first step in the thermo-oxidative degradation; in addition, the presence of HBPSi in BCE resin also significantly reduces the mass loss rate (MLR) and increases char yield at 800 °C under an air atmosphere. Therefore, the positive effect of HBPSi on improving the flame retardancy is attributed to the condensed phase mechanism. On the other hand, HBPSi/BCE resins exhibit improved dielectric properties (including decreased dielectric constant and loss) with increasing the content of HBPSi. More importantly, this investigation demonstrates that designing new polysiloxane with suitable chemical structure is important to develop high performance resins with attractive flame retardancy and dielectric properties. [Copyright &y& Elsevier]

Abstract: A novel modified bismaleimide resin system (BDP) with significantly improved flame retardancy and decreased dielectric loss was successfully prepared by copolymerizing 4,4′-bismaleimidodiphenyl methane (BDM) with 2,2′-diallyl bisphenol A (DBA) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Compared with BDM/DBA resin, BDP resin has obviously different crosslinked structure, and thus simultaneously improved dielectric properties and flame retardancy. Most attractively, with a very low content of phosphorus element, the BDP resins show significantly improved flame retardancy. For example, when the content of phosphorus is as low as 0.5 wt%, the flame retardancy of BDP resin is evaluated to be UL94 V-0 level, while that of BD resin is classified as UL94 V-1 level; in addition, the total heat release (THR) of BDP resin reduces to about 61% of that of BD resin, and similar phenomenon is also observed on the weight ratio of CO/CO2. This outstanding flame retardancy of BDP resins is attributed to the attractive phosphorus-nitrogen synergistic effect. The main flame retardancy mechanism of BDP resins is evaluated to be condensed phase mechanisms. On the other hand, BDP resins exhibit improved dielectric properties; specifically, the dielectric constant and loss at 1 GHz of BDP resin with 19.7 wt% of phosphorus are 2.90 and 0.0058, only about 92% and 51% of that of neat BD resin, respectively. These interesting results demonstrate that the co-reaction of DOPO with BD resin is important, and the method proposed herein is a new approach to develop high performance resins with attractive flame retardancy and dielectric properties. [Copyright &y& Elsevier]