Abstract
Polyphenylsilsesquioxane (PhSiO3/2) particles as an organic-inorganic hybrid were prepared using sol-gel method, and monolithic samples were obtained via a warm-pressing. The reaction mechanism of particles’ polymerization and transformation to the monolith under the warm-press were investigated using solid state 29Si nuclear magnetic resonance (NMR) spectrometer, thermal gravimetric-differential thermal analyzer (TG-DTA), mass spectrometer (MS) and scanning electron microscope (SEM). Transparent and void-free monoliths are successfully obtained by warm-pressing above 180 °C. Both the terminal –OH groups on particles’ surface and warm-pressing are necessary for preparation of void-free PhSiO3/2 monolith. From the load-displacement measurement at various temperatures, a viscoelastic deformation is seen for PhSiO3/2 monolith with voids. On the other hand, an elastic deformation is seen for void-free PhSiO3/2 monolith, and the void-free monolith shows much higher breakdown voltage.
Highlights
An organic-inorganic hybrid of polyphenylsilsesquioxane (PPSQ, PhSiO3/2 ) has attracted much attention owing to its unique thermal softening and curing properties since Brown et al reported the PhSiO3/2 as a ladder polymer with a stereoregular double chain structure in 1960 [1,2,3,4,5,6]
We found an enhancement of the alternating current (AC)
A transparent and void free monolith was obtained at 180 ◦ C, and the second cycle behavior of which can be expressed only by a spring element. These results strongly suggest that the viscoelastic response induced by the dashpot element at the second cycle is correlated strongly with voids between PhSiO3/2 particles’ interfaces
Summary
An organic-inorganic hybrid of polyphenylsilsesquioxane (PPSQ, PhSiO3/2 ) has attracted much attention owing to its unique thermal softening and curing properties since Brown et al reported the PhSiO3/2 as a ladder polymer with a stereoregular double chain structure in 1960 [1,2,3,4,5,6]. Materials 2018, 11, 846 the insulating layer [24,25] Due to their susceptibility to crack generation during prolonged operation and their high fabrication cost, composite insulating layers consisting with epoxy resin and ceramic filler (e.g., boron nitride) for increasing thermal conductivity have been developed so far [26]. SiC-based power devices have various advantages including high frequency operation, high thermal conductivity, high breakdown voltage and high-temperature operating capability higher than 200 ◦ C owing to its wide bandgap compared with silicon [29,30]. From the view point of increasing the operation temperature, we anticipated that PhSiO3/2 will be a candidate for the insulating layer instead of epoxy resin due to its high thermal stability.
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