Preparation, Structutre And Properties Of Nanocomposites Based On Cyanate Ester Resin

Cyanate ester resin (CE) possesses very low dielectric constant and dielectric loss in wide temperature and frequency ranges. It has also balanced heat resistance and processing properties. As a result, CE is proposed to be a promising resin for high performance composites. However, the toughness and modulus of CE are not satisfied. The purpose of this thesis is to develop new kinds of CE-based composites with excellent mechanical, thermal and dielectric properties through adding inorganic particles. It is also desirable to provide a fundamental understanding about the inorganic particle-modification of cyanate ester systems, such as the influence on curing reaction and the relationship between the structure and properties.In the first part, silicate nanorods (attapulgite, ATT) were organically modified and homogeneously dispersed in a cyanante ester (CE) resin. ATT dispersions and networks were characterized by rheological and microscopic measurements. Amine groups grafted onto the particle surface catalyzed the cyclotrimerization of the CE monomers, and enabled the CE monomers to easily enter the inter-rod spacing of loose aggregates, resulting in homogenization of the particle size distribution in the nanocomposites. The percolation threshold concentration of ATT in cyanate ester monomers was around 10wt%, and the addition of ATT will remarkable increased the viscosity of system-the viscosity of 8wt% mixture was 10 floders higher than the neat monomers. Because of the diffusion control character of cyanate ester curing, the higher viscosity might induce the cyclotrimerization reaction activity after geltion. Therefore, the addition of nanorods decreased the density of organic networks and increased intracyclizations. Isourea covalent bonding at the interface was confirmed by FTIR and DMA, which establishes a basis for optimizing mechanical properties of CE resins. According to the reaction mechanism between cyanate and amine group, different propable reaction routes are proposed, and reasonably explaine the gradual disappear of isourea structure with curing proceeds. Nanocomposite modulus, strength and toughness increased 40, 42 and 55% relative to the neat resin, although high particle loadings showed negligible benefit. The interplay between particles and resin networks governed the mechanical properties of the nanocomposites. A hybrid network module was proposed to explaine the relationship between the structure and properties of nanocomposites with the increasing loadings of ATT.In the second part, organo-derivative of POM particles was prepared according to the method used before in our team. And the inorganic/organic cyanate ester nanocomposites thin films were firstly prepared through solvent mixing. The dielectric properties were improved e.g. dielectric contant and loss both decreased with the addition of POM. It was found the POM particles make catalytic effect on cyanate ester curing by DSC characterization. TEM images testified the homogeneous dispersion of POM in ester matrix and the composites thin films maintain good light-permeation properties. The tensile modulus also increased based on the DMA measurement.