Benfridja Imadeddine, Diaham Sombel, Laffir Fathima, Brennan Grace, Liu Ning, Kennedy Tadhg
Department of Chemical Sciences, University of Limerick, Limerick V94 T9PX, Ireland.
Bernal Institute, University of Limerick, Limerick V94 T9PX, Ireland.
Polymers (Basel). 2022 Apr 22;14(9):1713. doi: 10.3390/polym14091713.
Polyimides (PI) are a class of dielectric polymer used in a wide range of electronics and electrical engineering applications from low-voltage microelectronics to high voltage isolation. They are well appreciated because of their excellent thermal, electrical, and mechanical properties, each of which need to be optimized uniquely depending on the end application. For example, for high-voltage applications, the final polymer breakdown field and dielectric properties must be optimized, both of which are dependent on the curing process and the final physico-chemical properties of PI. The majority of studies to date have focused on a limited set of properties of the polymer and have analyzed the effect of curing from a physicochemical-, mechanical- or electrical-centric viewpoint. This paper seeks to overcome this, unifying all of these characterizations in the same study to accurately describe the universal effect of the cure temperature on the properties of PI and at an industrial processing scale. This paper reports the widest-ranging study of its kind on the effect that cure temperature has on the physico-chemical, mechanical, thermal and electrical properties of polyimide, specifically poly (pyromellitic dianhydride-co-4, 4'-oxydianiline) (PMDA/ODA). The optimization of the cure temperature is accurately studied not only regarding the degree of imidization (DOI), but also considering the entire physical properties. Particularly, the analysis elucidates the key role of the charge-transfer complex (CTC) on these properties. The results show that while the thermal and mechanical properties improve with both DOI and CTC formation, the electrical properties, particularly at high field conditions, show an antagonistic behavior enhancing with increasing DOI while degrading at higher temperatures as the CTC formation increases. The electrical characterization at low field presents an enhancement of the final PI properties likely due to the DOI. On the contrary, at high electric field, the conductivity results show an improvement at an intermediate temperature emphasizing an ideal compromise between a high DOI and PI chain packing when the thermal imidization process is performed over this equilibrium. This balance enables maximum performance to be obtained for the PI film with optimized electrical properties and, overall, optimal thermal and mechanical properties are achieved.
聚酰亚胺（PI）是一类介电聚合物，广泛应用于从低压微电子到高压绝缘等众多电子和电气工程领域。由于其优异的热、电和机械性能，它们备受青睐，而每种性能都需要根据最终应用进行独特优化。例如，对于高压应用，必须优化最终聚合物的击穿场强和介电性能，这两者都取决于固化过程以及PI的最终物理化学性质。迄今为止，大多数研究都集中在聚合物的一组有限性能上，并从物理化学、机械或电学中心观点分析固化的影响。本文旨在克服这一问题，在同一研究中统一所有这些表征，以准确描述固化温度对PI性能的普遍影响，并达到工业加工规模。本文报道了同类研究中关于固化温度对聚酰亚胺，特别是聚（均苯四甲酸二酐 - 共 - 4,4'-氧二苯胺）（PMDA/ODA）的物理化学、机械、热和电性能影响的最广泛研究。不仅针对亚胺化程度（DOI），而且考虑整个物理性能，对固化温度的优化进行了精确研究。特别是，分析阐明了电荷转移络合物（CTC）在这些性能上的关键作用。结果表明，虽然热性能和机械性能随着DOI和CTC的形成而提高，但电性能，特别是在高场条件下，表现出相反的行为，随着DOI的增加而增强，而随着CTC形成的增加在较高温度下会下降。低场下的电学表征表明最终PI性能可能由于DOI而增强。相反，在高电场下，电导率结果表明在中间温度下有所改善，强调了在进行热亚胺化过程超过此平衡时，高DOI和PI链堆积之间的理想折衷。这种平衡能够使PI薄膜获得具有优化电性能的最大性能，并且总体上实现最佳的热性能和机械性能。
