| Conductor/polymer high-k nanocomposites(hi-k CPNC) have been an important type of functional materials. However, high percolation threshold(fc), high dielectric loss, low breakdown strength(Eb) and energy storage density(We) are the key problems of hi-k CPNCs available. Therefore, it still remains a big challenge to fabricate novel hi-k CPNCs with outstanding dielectric properties by improving the dispersion of conductors in the polymer matrix through constructing novel morphological structure.Firstly, it is an important way to prepare new generation high performance resins through blending/copolymerizing engineering thermoplastics(TP) with thermally resistant thermosetting(TS) resins. The morphological structure is the key to determine the performances of TP/TS system. However, the poor processing feature of TP, such as high viscosity and melting temperature, less reactive groups and poor solubility in common solvents, makes an inferior repeatability of the morphology of TP/TS system. In this thesis, cyanate ester(CE) resin, known as the most potential resin to prepare structural/functional materials in the 21 st century, was chosen as the TS resin, and phenolphthalein type polyarylether sulfone(cPES) as the TP. A series of cPES/CE resins were prepared through facilely melt-blending CE resin with cPES. The phenolphthalein pendant and hydroxyl groups of cPES provide good compatibility between CE resin and cPES under small contents(≤10wt%) of cPES, achieving the control of the morphological structure through adjusting the content of cPES and ensuring the good manufacturability. The chemical and aggregation structures(morphological structure, crosslinking density, free volume) and integrated performances(curing reactivity, mechanical, dielectric and thermal properties, flame retardancy) were systematically investigated. Results show that cPES is an efficient toughening agent of CE resin. Compared with CE resin, 10cPES/CE and 20cPES/CE resins have 1.4 and 3.2 times higher impact strengths, respectively. In addition, cPES/CE resins have better thermal stability, dielectric properties and modulus. The flame retardancy of CE and cPES/CE resins were systematically evaluated through analyzing thermogravimetric kinetics, thermogravimetric analysis-infrared and cone calorimeter tests. Results show that the addition of cPES into CE resin brings greatly increased difficulty of catching fire. While once ignited, cPES/CE resin exhibits a bigger heat release rate and total heat release. The origin behind was systematically revealed through discussing the influence of cPES on the morphological structure of the system.Secondly, on the basis of the study of the morphological structure of cPES/CE resins, a fully compatible and transparent polymer blend consisting of cPES and CE(w/w=10/90) was specially designed as the resin matrix, and then new conductor/polymer composites based on multi-walled carbon nanotubes(MWCNTs) and cPES/CE were prepared through a two-step method, constructing a novel morphological structure. The effect of morphological structure on dielectric properties, Eb and We of MWCNT/CE and MWCNT/CE/cPES composites were systematically studied. Compared with MWCNT/CE composites, MWCNT/CE/cPES composites have a much lower fc that is as low as 0.89wt%, only about 0.25 times of that of MWCNT/CE composites; besides, MWCNT/CE/cPES composites possess greatly improved dielectric constant, much larger Eb and We as well as greatly decreased dielectric loss. The origin behind these desirable properties was discussed through investigating the morphological structure and building equivalent circuits. These interesting results demonstrate that this project reported herein provides a simple way to prepare hi-k CPNCs with excellent comprehensive dielectric properties through building novel morphological structures. |
PDF Full Text Request