Revealing molecular mechanisms of colorless transparent polyimide films under photo-oxidation
Revealing molecular mechanisms of colorless transparent polyimide films under photo-oxidation
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DOI：
10.1016/j.polymdegradstab.2023.110294
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发表时间：
2023-02-21
影响因子：
5.9
通讯作者：
Kong, Miqiu
中科院分区：
文献类型：
--
作者：
Feng, Jiabao;Wang, Yi;Kong, Miqiu
无色透明聚酰亚胺（CPI）薄膜具有高的热稳定性、优异的上级力学性能和介电性能，广泛应用于光电器件中，但在使用过程中会出现性能下降。本工作揭示了三氟甲基结构的CPI-L膜和脂环基结构的CPI-T膜在光氧化条件下的性能退化及其分子机理。结果表明，CPI-L和CPI-T薄膜经168 h光氧化后，力学性能和热稳定性均有所下降，黄度指数分别增加了740%和530%。因此，在光氧化之后，CPI-L膜的降解比CPI-T膜更严重。这是因为在光氧化之前，CPI-L和CPI-T膜在365 nm处的透射率分别为51%和64%。光氧化后，两种CPI膜的醚键、酰亚胺环和苯环均发生断裂，CPI-L膜中的C-N发生重排。在120 h和72 h时，出现了由排气引起的腐蚀空洞和/或微裂纹。提出了CPI薄膜光氧化过程中可能的分子机理，并阐明了分子机理与性能退化之间的关系。此外，随着CPI-L和CPI-T薄膜厚度的增加，C-O含量逐渐减少，表明C-O在薄膜表面富集。这主要是因为在光氧化过程中产生的自由基可以与大气中的O2联合收割机结合。
Colorless transparent polyimide (CPI) films with high thermal stability, superior mechanical and dielectric properties are widely used in optoelectronic devices, in which the properties are degraded in service. In this work, the degradation in properties and molecular mechanisms of the CPI-L film with the trifluoromethyl group and CPI-T film with the alicyclic group under photo-oxidation are revealed. It is found that for CPI-L and CPI-T films after 168 h photo-oxidation, the mechanical properties and thermal stability are decreased, especially the yellowness index is increased by 740% and 530%, respectively. Consequently, the degradation of the CPI-L film is more severe than the CPI-T film after photo-oxidation. This is because that the transmission at 365 nm of CPI-L and CPI-T films before photo-oxidation is 51% and 64%, respectively. After photo-oxidation, the ether bond, imide ring and phenyl of both CPI films are broken, and the rearrangement of C-N in the CPI-L film is observed. And eroded voids and/or microcracks caused by off-gassing appear at 120 h and 72 h, respectively. Furthermore, possible molecular mechanisms of CPI films during photo-oxidation are proposed, and the relationship between molecular mechanisms and properties degradation is elucidated. Moreover, the content of the C--O is decreased with the increased depth of CPI-L and CPI-T films, indicating the enrichment of the C--O on the surface. It is mainly because free radicals generated during photo-oxidation can combine with the atmospheric O2.