新型聚氯乙烯改性共聚物的合成及其多尺度聚集态结构与介电储能性能调控

As one of the most important parts of high pulse capacitors, polymer dielectric materials with high energy storage and low dielectric loss properties exhibit huge value and demands in the national economy and national defense construction. Limited by the synthesis method and the thin films fabrication technology, the current dielectric polymers could hardly balance the high energy storage density and low energy loss. Especially, the understanding of the relationship between the aggregation state of these materials in multi scale and their dielectric and energy storage properties is rather poor. Therefore, in this program, we would like to develop a series of chemical modification methods for poly(vinyl chloride) (PVC) to synthesize two families of copolymers including one is based on PVC as main polymer chain and polyethylene (PE) is as main chain in the other family of copolymers. The modified copolymers would solve the problems such as low thermal stability of PVC and the difficulty in functionalization of PE in traditional way. The dielectric constant, aggregation state in multi scale and the energy storage properties of the copolymers could be tuned in a large scale by controlling the amount and type of polar groups introduced as well as the film fabrication conditions. The deep and new understanding of the relationship between the composition, aggregation state and the electrical properties of these materials would be constructed. At the same time, the new mechanism of balancing the high energy storage and low energy loss would be disclosed, which may guide the design and development of novel high energy density dielectric materials in the future.

具有高储能密度、低能量损耗的聚合物电介质材料是高储能放电电容器中最重要的组成部分，在国民经济和国防建设中具有重要应用价值和巨大需求。受制于合成方法和薄膜加工工艺，现有聚合物在高储能密度和低能量损耗两个方面往往难以兼顾。基于目前对电介质材料中聚合物多尺度聚集态结构与其介电储能性能之间关系认识的不足，本项目拟以聚氯乙烯（PVC）为基础原料，通过化学改性新方法研究，制备出分别以PVC和聚乙烯为主链的新型接枝聚合物，解决PVC热稳定性差和聚烯烃难以功能化的难题。通过对接枝基团极性和含量的调节以及薄膜制备方法的优化实现对改性聚合物介电常数、储能、高压绝缘等特性在较宽范围内的调控，建立对聚合物化学组成、多尺度聚集态结构与其电性能之间关系的新认识，阐明调和此类聚合物高储能密度和低能量损耗之间矛盾的新机制，为高储能低损耗聚合物电介质的设计制备提供理论指导。

具有高储能密度、低能量损耗的聚合物电介质材料是高储能电容器中最重要的组成部分，在国民经济和国防建设中具有重要的应用。受制于合成方法和加工工艺，现有聚合物在高储能密度和低能量损耗两个方面难以兼顾。基于目前对聚合物电介质材料的结构与储能性能的研究，本项目采用乳液聚合、取代、可控自由基聚合及还原反应等方法制备出一系列极性可调、偶极矩排列可控的电介质材料，实现了聚合物的介电、储能性能在较宽范围内的调控。首先，采用可控自由基聚合法在聚氯乙烯（PVC）侧链上接枝聚甲基丙烯酸甲酯（PMMA）链段，得到的PVC-g-PMMA接枝共聚物的击穿电场为557 MV/m且分布更集中，材料使用可靠性增强；其次，采用氯化取代反应将聚乙烯（PE）主链上的C-H键部分取代为C-Cl键，制备出氯化聚乙烯（CPE）。其介电常数为3~4，储能密度（Ue）和能量损耗（Ul）在700 MV/m的电场下分别为12 J/cm3和17%；随后，以苯乙烯（St）和甲基丙烯酸甲酯（MMA）为共聚单体合成系列不同组成的聚（苯乙烯-甲基丙烯酸甲酯）（P(St-MMA)）共聚物。通过合理调控极性基团的聚集以减少相互之间的耦合作用，实现偶极极化弛豫的最小化，达到降低聚合物损耗的目的，得到的P(St-MMA)共聚物的介电常数在3~4。当MMA含量为45 mol%时，Ue在550 MV/m电场下为12.2 J/cm3，Ul仅为8%；最后，通过还原反应在PMMA和P(St-MMA)中引入一定量羟基来减小极性基团的β驰豫，并且引入的-OH之间或者-OH与酯基间形成氢键，使得共聚物的模量提高。所得聚（甲基丙烯酸甲酯-甲基丙烯醇）（P(MMA-MAA)）共聚物在550 MV/m电场下，Ue可达13 J/cm3，而Ul仅为8%。聚（苯乙烯-甲基丙烯酸甲酯-甲基丙烯醇）（P(St-MMA-MAA)）共聚物介电常数为3~6，700 MV/m电场下Ue可达14.5 J/cm3，而Ul仅为7%。同时，低极性St的存在，在聚合物中可以有效屏蔽极性基团间的相互作用，从而降低由极性基团聚集引起的损耗。通过对合成的聚合物的基团极性和含量的调节以及薄膜制备方法的优化实现对改性聚合物介电常数、储能等性能在较宽范围内的调控，为高储能低损耗聚合物电介质的设计提供理论指导。