On Novel Manual Dielectrics Based On Cyanate Ester Resin

Manual dielectrics are key materials for Pulse Doppler (PD) radar redome, which should have low density, good thermal resistance, adjustable dielectric constant and high mechanical properties. It is important to develop high performance manual dielectrics to meet the requirements for advanced PD redoes. In general, manual dielectrics are composites made up of organic matrix and functional fillers. It is known that the matrix is not only the basic component of a composite, but also the key factor for determining the main properties of the composites such as thermal resistance, dielectric property, processing characteristics and interfacial shear strength, so high performance matrices must be employed to develop advanced manual dielectrics.Cyanate esters (CEs) are derivatives of compounds containing two or more cyanate (-OCN) functional groups, which have excellent dielectric properties, especially low and stable dielectric constant and dielectric loss over a wide range of temperature (0-220℃) and frequency. (0-1011Hz), outstanding thermal and moisture resistance, good adhesion as well as good processing characteristics, so CE resins have been considered as"the most competitive resins for developing structural/functional materials in 21st century", showing great potential in many fields including aviation and aerospace, electric and transportation.In this thesis, the new idea of developing high performance manual dielectrics based on CE resins is proposed in the first time, binary composites and ternary composites were designed and prepared. The main factors which have influences on structure and properties of these composites were intensively discussed, and the structure-property relationship was primly developed to supply new theoretic and technological bases. No similar investigations have been found in the literatures.For Rutile/CE composites, the effects of the surface nature and content of rutile on the curing behavior and physical/mechanical properties were discussed. Results show that the surface nature of rutile has significant influences on the curing behavior of CE. The rutiles treated by the coupling agent, KH550 or NDZ-401, coded as Rutile(KH5500) or Rutile (NDZ-401), respectively, have active groups, so they can effectively catalyst the gelation of CE. On the other hand, the presence of rutiles also increases the activation energy of the curing reaction, so the resultant system requires greater activation energy for curing after gelation. In addition, CE and all composites have the same reaction order. The dielectric constant of compostes can be adjusted between 2.95 and 8.81 by controlling Rutile(KH550) content. When Rutile(KH550) content is not bigger than 40wt%, the Lichteneker equation can be used to predict the dielectric constant of the composites. Rutile(KH550) content also has obvious effect on the dielectric loss of composites. When Rutile(KH550) content is less than 30wt%, the dielectric loss of the composite is lower than that of CE resin; when Rutile(KH550) content increases to 40wt%, the dielectric loss of composites tends to have stable value. At last the addition of Rutile(KH550) into CE resin is beneifical to improve the thermal stability.For hollow glass beads/CE composites, the effects of the surface nature and content of hollow glass beads on the density, statistic and dynamic mechanical properties, thermal and dielectric properties were mainly discussed. Results show that no matter what their nature is, hollow glass beads can decrease dielectric constant (ε), dielectric loss (tanδ)and thermal expansion coefficient (CTE). HGB(KH550) has bigger influence on decreasing the density, water-absorption of composites than HGB, while HGB tends to have slightly bigger ability to decrease both values ofεand tanδ. HGB(KH550) can effectively decrease the density and water-absorption of materials. 4wt%HGB(KH550) slightly increases the initial decomposition temperature; with continuous increase of HGB(KH550) content, the temperature for the maximum decomposition rate of composites is similar as that of CE resin, but the char yields of composites are greater than the theoretical dataFor Rutile(KH550)/HGB(KH550)/CE composites, the effect of the formulations of composites on the density, dielectric properties, thermal expansion coefficient and the dynamic mechanical properties of the composites were emphasized investigated. Results show that bothεand tanδvalues as well as CTE of Rutile(KH550)/HGB(KH550)/CE composites are lower than those of CE resin, and can be effectively adjusted by controlling the formulations of composites.. When the weight ratio of fillers and resin is 1:3, by varying the weight ratio of Rutile(KH550) and HGB(KH550) from 0.2:1 to 1:0.2, then the density, tanδorεof composites change between 0.68 and 1.17g/cm3, 0.004-0.010 or 2.90-3.74, respectively. The damping factor peaks of all Rutile(KH550)/HGB(KH550)/CE composites are made up of a main peak plus a small shoulder, their corresponding Tg values almost do not change with the formulation of the composites.