基于环丁烷四甲酸酐的脂环聚酰亚胺介电性能研究

Dielectric Properties of Alicyclic Polyimides Derived from Cyclobutane-1,2,3,4-tetracarboxylic Dianhydride

商品化聚酰亚胺由于含碳量高,发生击穿时容易产生积碳导致相应的金属化薄膜电容器层间短路失效.为改善这一问题,从分子设计出发,选用含四元脂环结构的环丁烷四甲酸二酐(CBDA)作为二酐单体,向聚酰亚胺分子结构中引入低碳氢比的脂环结构,制备脂环聚酰亚胺,其介电性能优异,介电常数为3.83~4.74,损耗因子为0.49%~1.29%,最高击穿场强和理论能量密度分别为547 MV/m和5.91 J/cm3.并且,由于碳氢比降至1.16~1.29,远低于商品化聚酰亚胺,大大改善击穿点处的积炭行为,从而有利于相应金属化薄膜电容器的自愈性.

Carbon deposition tends to occur in commercial polyimide during electric breakdown due to the high carbon content,resulting in short circuit between interlayers of the corresponding metallized film capacitors.In order to solve this problem,molecular design is employed by introducing alicyclic structure with low carbon content into polyimides in this study.Specifically,the alicyclic polyimides(PI-1-PI-5)are prepared from alicyclic dianhydride of cyclobutane-1,2,3,4-tetracarboxylic dianhydride(CBDA)and aromatic diamines.Defect-free films derived from alicyclic polyimides are obtained whose chemical structures have been assigned by FTIR.In addition,it is indicated from the XRD results that the alicyclic polyimides are amorphous.When it comes to the dielectric properties,dielectric constants of 3.83-4.74(at 103 Hz)are achieved owing to the easier polarization of extranuclear electrons in cycloalkane structure in alicyclic polyimides compared to the all-aromatic polyimide such as Kapton(ε_(r)=3.5).Besides,the values of dissipation factor are in the range of 0.49%to 1.29%(at 103 Hz).The flexible alicyclic structure contributes to frictionless reorientation and low dielectric loss.The band gap of 3.96-4.13 eV and Weibull breakdown strength of 243-547 MV/m in the alicyclic polyimides are acquired.As a result,the highest theoretical energy density is as high as 5.91 J/cm3 obtained in PI-3.The last but not the least,thanks to the reduced carbon content(carbon-hydrogen ratio:1.16-1.29),compared to the commercial polyimide of Kapton(carbon-hydrogen ratio:1.60),carbon deposition behavior has been greatly suppressed because the hydrogen and oxygen elements would escape easily from the breakdown point in the form of water vapor under the high-temperature arc.Furthermore,the dielectric films of alicyclic polyimides would facilitate the self-healing behavior of the corresponding metallized film capacitor.