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At First, a poly(amic acid) (PAA) based on pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) was prepared by polycondensation procedure, and the PAA/SiO2 composite solutions were obtained by adding different mass fraction of colloidal SiO2/N,N-dimethylacetamide (DMAc) during the polymerization. Then a series of PI/SiO2 composite films were prepared by thermal imidization of the PAA/SiO2 composite solutions in a clean oven from room temperature to 350℃ in nitrogen. The PI composite films were characterized by the attenuated total reflectance Fourier transform infrared (ATR-FTIR), scanning electron microscopy (SEM), thermal-gravimetric analysis (TGA), dynamic mechanical analysis (DMA), and thermo-mechanical analysis (TMA), and the effect of SiO2 on the dielectric properties of composite film was tested by the impedance analysis measurement. The results show that the composite films with expected structure are prepared, and the SiO2 disperses in PI matrix uniformly. The incorporation of SiO2 improves the heat resistance and dimensional stability at high temperature of the PI composite films. The 5% weight loss temperature (T5%) and 750℃ residual weight ratio (Rw750) of the PI-25 film with 25% of SiO2 are 611.3℃ and 73.1%, respectively, which are 14.7℃ and 9.2% higher than those of the PI-0 film (without silica). The PI composite films exhibit stable dielectric constant (Dk) and dielectric loss factor (Df) in the frequency range of 103-106 Hz. The incorporation of nano-silica slightly increases the Dk of composite films, and the Dk of the PI-25 film at 1 MHz is 3.58, which is a bit higher than that of the PI-0 film (Dk is 3.20).
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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