Study On Modified Cyanate Ester Resin

Cyanate ester resin (CE) possesses very low dielectric constant and dielectric loss in a wide temperature and frequency range. It has also balanced heat resistance and processing properties. As a consequence, CE is suggested to be a potential resin for high performance composites. However, the toughness and modulus of CE are not satisfied. The purpose of this work is to develop a new kind of CE-based composite with excellent mechanical, thermal and dielectric properties. It is also of value to provide a broad understanding about the modification of other thermoset polymer systems.This dissertation is composed of four parts. First, study on the curing kinetics of cyanate and epoxy resin (EP) blend; second, study on the intercalated (or exfoliated) nanocomposite of CE and amino-bentonite (BT); third, further modification based on the carboxyl terminated liquid nitrile rubber (CTBN) modified cyanate ester resin system; fourth, study on the free volume of the system by positron annihilation lifetime (PAL) spectroscopy.In the first part, curing process of the binary blends consisting of different amount of cyanate ester and epoxy resin was studied by the means of differential scanning calorimetry (DSC) and Fourier transform infrared analysis (FTIR). The apparent activation energy values of CE/EP blends with mass ratio of 10/0, 9/1, 7/3, and 5/5 obtained by Ozawa treatment of DSC results equal to 74.3, 72.1, 60.8 and 72.7kJ/mol, respectively. Incorporation of small amount of epoxy resin could accelerate the curing process of cyanate ester. Kinetic parameter obtained by FTIR is in good agreement with that by DSC. Furthermore, it was found that the transformation of cyanate group is much faster than that of epoxy group during curing process and the curing process is a first-order reaction for both cyanate group and epoxy group.In the second part, intercalated and exfoliated structures of anmino-bentonite in cyanate ester resin has been investigated, the intercalation and exfoliation mechanism was discussed. The results revealed that the amino-bentonites were easy to be intercalated by cyanate oligomer to form a stable CE/bentonite intercalated hybrid. Partially exfoliated and partially intercalated CE/NH4+-BT nanocomposites were obtained via a melt blending process. The impact strength and thermostability of CE were improved simultaneously with the loading of NH4+-BT. The impact strength showed a maximum of 7.1kJ/m at lphr BT loading, comparing to 3.8kJ/m of pure CE. The exfoliated BT had the best toughening effect, whereas the aggregate BT particles may deteriorated it. Also, results of thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) suggest that CE/BT nanocomposites has higher thermal stability and modulus.In the third part, CTBN modified cyanate system and accordingly toughening mechanism were first discussed. Then, further modifications base on such a system were performed. Results show that the addition of CTBN does increase the impact strength significantly but with sacrifice of modulus and thermostability. TGA curve of CTBN and SEM picture of fracture surface indicated the existence of cavities. TEM observations verified the presence of CTBN rubber-particles. Hence, it is concluded that rubber-particle and cavities toughening mechanism function together to improve the toughness of CE. Addition of appropriate amount of epoxy resin (EP) in CE/CTBN system can not only increase the modulus and thermostability of the blend, but also improve the toughness. Good result ascribe from the fact that the addition of EP plays a key role to improve the miscibility of CE/CTBN/EP blends. It was found that a combination of intercalated and exfoliated structures of BT existed in CE/CTBN/BT composites while rubber particles also can be observed in CE/CTBN/BT composites by TEM. Addition of appropriate amount of BT in CE/CTBN system could not only obviously increase the modulus of the blend without sacrifice of toughness, but also improve the thermostability. The modulus increased from about 2100MPa of CE/CTBN (100/...