Toughening Of Cyanate Ester Resins

Cyanate ester (CE) resin is one kind of the most important engineering thermosetting polymers, and has received great attentions due to its outstanding integrate properties, such as good mechanical properties, outstanding thermal resistance, excellent dielectric property as well as low water absorption. 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 like most thermosetting resins, the inherent brittleness is the major drawback of CE resin, which is also the major disadvantage to restrict further prosperity of CE resin into the advanced industrial applications. So toughening has been the main subject associated with the investigation of CE resin for many years.In this thesis, a hyperbranched polysiloxane (HBPSi) derived from the hydrolysis of 3-(trimethoxysilyl)propyl methacrylate was synthesized. We respectively used HBPSi and a combined modifier (HBPSiEP) made up of HBPSi and EP to toughen CE resin, in addition, the relationship of structure and properties of the developed resins is intensively investigated. The main research contents and results can be described as follows:Designing, synthesis and the discussions of structure-property relationship of HBPSi. FTIR and 1H-NMR techniques were used to analyze the molecular structure of HBPSi, results show that KH570 successfully changes into a transparent yellow liquid (HBPSi) through the hydrolysis. In addition, the study about the effect of molar ratio (m) of distilled water and KH570 on the molecular weight and viscosity of HBPSi shows that both molecular weight and viscosity of HBPSi increase gradually with the increase of m value.Designing and preparation of HBPSi/CE resins, moreover, the investigation about the effect of the stoichiometry between CE and HBPSi on the structure and property of modified CE resins. Intensive researches on processing performance, micro-morphology, toughness, thermal resistance, dielectric properties and water absorption show that the incorporation of HBPSi can not only effectively promote the curing reaction of CE, but also increase the apparent free volume fraction of the cured network, and thus effectively decreases cross-linked degree of rigid triazine rings. More important, the impact strength of modified CE resin with 15wt% of HBPSi is more than 2 times of that of pure CE resin and the SEM images of cross-sectional surfaces of samples after impact appear a large amount of ductile sunken areas. In addition, the toughened CE resin also exhibits better thermal stability, dielectric property and moisture resistance.Designing and preparation of HBPSiEP/CE resins, and the evaluation of the effect of the differing stoichiometry of HBPSiEP on the curing characteristics and performance of CE resin. Results show that the incorporation of HBPSiEP can not only effectively promote the curing reaction of CE, but also significantly improve the toughness of cured CE resin. In addition, the toughening effect of HBPSiEP is greater than single EP resin. For example, the impact strength of modified CE resin with 30wt% of HBPSiEP is 23.3kJ/m~2, which is more than 2.5 times of that of pure CE resin, while the maximum impact strength of EP/CE resin is about 2 times of pure CE resin. It is worthy to note that HBPSiEP/CE resins also exhibit higher bending strength, improved thermal stability, flame retardancy, lower water absorption and excellent dielectric properties.This paper gives the first report on toughening CE resin by introducing hyperbranched polymers. The novel toughened CE resins have great potentiality to be used as matrices for advanced functional composites or electronic packing resins, which have very important significance for the development and wide application of CE resins. In addition, the new method proposed in this work for modifying CE resins by hyperbranched polymers maybe has directive function for the researches of other thermosetting resins.