Study Of Novel Modified Cyanate Ester Resin Based On Hyperbranched Technology

Cyanate ester (CE) resins are derivatives of compounds containing two or more cyanate functional groups (?O?C≡N). Cured CE resins possess a good combination of excellent dielectric properties, high thermal stability and good mechanical property. In addition, CE resins have very good adhesion, and almost the lowest moisture absorption among thermosets. Therefore, CE resins have been considered as―the most competitive resin for preparing advanced structural and functional materials in 21st century‖, showing great potential in many fields including aviation and aerospace, electric and transportation. However, being a thermosetting resin, the inherent brittleness is the major drawback of CE resins, which are the major disadvantages to restrict further prosperity of CEs into the advanced industrial applications.In this thesis, a reactive hyperbranched polysiloxane (HPSiE) with epoxy groups was designed and synthesized via the hydrolyzation of KH-560 and water, and its structure and properties were characterized. HPSiE was used to develop a novel high performance HPSiE/CE resin, in addition, the effect of HPSiE content on the processing characteristics and properties of HPSiE/CE resins were investigated intensively. In order to improve the thermal stability of HPSiE/CE resin, bismaleimide/diallyl bisphenol A (coded as BD) was introduced by copolymerizing to prepareCE/BD/HPSiE resins, of which the key properties were systemicly investigated. Acid is used as the catalyst to speed up the hydrolysis process. In order to study the effect of molar ratio (m) of H2O and KH-560 on of the properties of HPSiE, six m (1.1—1.6) were designed. Reslults show that the molecular weight (Mw) and viscosity of HPSiE increase with the m value. Due to the moderate viscosity, HPSiE synthesized by using the m value of 1.5 was used as the example to study the synthesizing process. The results from IR,1H-NMR and 29Si-NMR indicate that methoxy groups have transformed into silicon oxidation groups successfully.For HPSiE/CE resins, the effects of HPSiE concentration on key properties such as toughness, thermal and dielectric properties as well water resistance were discussed in detail. Results reveal that the addition of HPSiE in CE resin can not only improve the toughness and water resistance of CE resin, but also display obvious catalytic effect on the curing reaction of neat CE. Moreover, these positive effects increase with the increase of HPSiE concentration in HPSiE/CE resins. In addition, with the increase of HPSiE content in HPSiE/CE resins, both the dielectric constant and loss increase slightly, while the thermal resistance decreases. It is need to point that the char yields of HPSiE/CE resins were higher than neat CE resin, indicating better flame retardation. The HPSiE/CE resins with desirable HPSiE content have more outstanding integrate properties than neat CE resin.For CE/BD/HPSiE resins, the effect of the formulations on key properties mainly including mechanical, dielectric and thermal properties, etc, was emphasized investigated. Results show that there is an optimum stoichiometry between BD and HPSiE for obtaining the maximum impact strength (which is about 1.5 times of that of original CE/BD resin), and CE/BD/HPSiE resins have much better water resistance than CE/BD resin. With the increase of HPSiE content in CE/BD/HPSiE resins, the coefficient of thermal expansion increases, and thermal resisitance decreases, while the dielectric constant and loss almost does not change. Comparing to HPSiE/CE resins, CE/BD/HPSiE resins with desirable HPSiE content show higher initial degradation temperature, or better thermal stability. In addition, these resins also have outstanding thermal and dielectric properties. These changes of properties are explained by an inherent feature of HPSiE, and the alteration of chemistry in network.