含苯硫醚基团的低介损聚酰亚胺薄膜合成及其性能调控机制

Synthesis and Performance Modification Mechanism of Low Dielectric Loss Polyimide Films With Phenyl Thioether Group

传统Kapton型聚酰亚胺薄膜在高频电应力下具有较高的介电损耗,难以满足高频电力变压器的绝缘需求。利用统计交替共聚法,制备含不同含量苯硫醚基团的聚酰亚胺薄膜,并对其结构、热学性质及介电特性进行测试。引入苯硫醚基团后,薄膜材料的介电损耗随苯硫醚含量的增加呈现先降低后升高的趋势,在40%含量时达到最低值(1k Hz时tan??0.000929),并保持热学性能不变,该趋势与紫外–可见光吸收光谱起峰波长的红移现象相一致。当含量较低时,苯硫醚基团可破坏聚酰亚胺分子间电荷转移络合作用(chargetransfercomplexes,CTC)的分散性,减弱松弛极化并离散极化时间分布,降低介电损耗;而随着苯硫醚基团含量增加,有较强失电子性能的硫元素会加强CTC,从而提高介电损耗。通过引入苯硫醚基团可影响聚酰亚胺的电荷转移络合作用,实现对其频域介电损耗特性的有效调控。

High dielectric loss of the Kapton-type polyimide film under high frequency electric stress does not make it a good fit to fulfill insulation requirements of the high frequency power transformers(HFPT). In this paper, the statistical alternating copolymerization method was used to prepare the polyimide films containing different ratio of phenyl thioether group units, and structure properties, as well as thermal and dielectric characteristics were obtained by experiments. The results indicate that, the dielectric loss of the film material decreases firstly but increases thereafter with increased content of phenyl thioether group. When the component ratio of phenyl thioether is 40%, the dielectric loss tangent reaches the lowest value(tan?? 0.000929 at 1 kHz),without sensible reduction of the thermal properties. The obtained dielectric loss variety trend is consistent with the redshift at the start-peak wavelength of the UV-Vis absorption spectrum. The phenyl thioether group can destroy the intermolecular charge transfer complexes(CTC) of the polyimide when the component ratio is low, which will weaken the relaxation polarization and disperse the polarization time distribution, leading to a lower dielectric loss. As thecomposition ratio of phenyl thioether group increases, sulfur elements with higher charge-loss ability will strengthen the CTC and hence increases the dielectric loss. The introduction of phenyl thioether groups can affect the charge transfer complexation of polyimides and thereby effectively modulate the dielectric loss characteristics in the frequency domain.