| Based on the import the foreign sciences and technologies and the independent research and development, the application of polymer materials of our country, related to the national economy, daily life and many respects of national security has been well developed. Cyanate ester resins (CE resins) with the outstanding properties like high temperature resistance, good mechanical properties and light weight have received widely attention. Despite possessing excellent advantages, CE resins are not suitable for many practical usages as their brittle and fragile characteristics caused by the highly cross-linked degree and the high rigidity of the triazine ring structure.In this study, hydroxyl-terminated polybutadiene (HTPB) was selected to modify the toughness of BEDCy Resin.Compared with other kinds of liquid rubbers, HTPB has good stability and moisture resistance without any ester or ether linkages in the molecular skeleton. Also it can be used as toughening agent for many thermosetting resins due to its flexible molecular chain. Additionally, the terminal hydroxyl of HTBP enable it reacted with wide species of chemicals.The viscosity change during the HTPB/CE pre-polymerization was observed by viscosity-meter. Influences on the gel time (determined from the results of this experiment) including the kinds of CE monomer, the kinds of solvent, the content of catalyst and the curing temperature, were all discussed according to the viscosity tests. The conclusion demonstrated that the with the better molecular symmetry, the reaction rate decreased leading a longer gel time; the reaction rate can be increased by suitable addition of the catalyst, modifier and HTPB loading as same as increased curing temperature, causing a accelerated reaction rate and a short gel time.Differential scanning calorimeter (DSC) was employed to carry out the multi-heating-rate dynamic cure experiments to calculate the dynamic parameters of the pure BEDCy resin curing system. The peak on the DSC spectrum corresponds to the exothermic cyclic trimerization of the CE monomer and the peak temperature increased with the temperature ramping rate. Base on the Kissinge's approach, the activation energy (Ea) of the pure BEDCy resin was calculated as 74.82 kJ/mol.The results of tensile stress-strain tests showed that the tensile strength gradually decreased with the increasing toughening agent HTPB loading; however the ultimate elongation was increased; and with the increase of the molecular weight of HTPB, the toughening effect turned better. As the high molecular weight HTPB loading attained 30 wt%, the toughening performance increased about 69%, with a rubber-like property. From the SEM image, it can be seen that the congeries of rubber molecular gradually phase separated from the resin system with the increasing rubber loading.When the rubber loading attained 40%, the SEM image showed a large number of crackles and cavities, causing the rubber-like mechanical properties, which had been mentioned in the toughening mechanism theories in the previous work. The results of thermogravimetric analysis (TGA) proved the addition of the HTPB toughening agent had inconspicuous influence on the thermal properties of CE resin, which can be an efficient toughing way. However the addition of the HTPB decreased the dielectric properties of the resin system with relatively stable performances on the wide frequencies scale. The dielectric behavior of toughening resins can basically satisfy the application requirement. Our work built a foundation for the BEDCy resins toughening as a new toughening area.
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