Wen Qian, Tang Ao, Chen Chengliang, Liu Yiwu, Xiao Chunguang, Tan Jinghua, Li Duxin
State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China.
Key Laboratory of Advanced Packaging Materials and Technology of Hunan Province, National and Local Joint Engineering Center of Advanced Packaging Materials R & D Technology, School of Packaging and Materials Engineering, Hunan University of Technology, Zhuzhou 412007, China.
Materials (Basel). 2021 Apr 21;14(9):2097. doi: 10.3390/ma14092097.
This study designed and synthesised a meta-amide-substituted dianiline monomer (m-DABA) as a stereoisomer of DABA, a previously investigated para-amide-substituted dianiline monomer. This new monomer was polymerised with pyromellitic dianhydride (PMDA) to prepare a polyimide film (m-DABPI) in a process similar to that employed in a previous study. The relationship between the substitution positions on the monomer and the gas barrier properties of the polyimide film was investigated via molecular simulation, wide-angle X-ray diffraction (WXRD), and positron annihilation lifetime spectroscopy (PALS) to gain deeper insights into the gas barrier mechanism. The results showed that compared with the para-substituted DABPI, the m-DABPI exhibited better gas barrier properties, with a water vapour transmission rate (WVTR) and an oxygen transmission rate (OTR) as low as 2.8 g·m·d and 3.3 cm·m·d, respectively. This was because the meta-linked polyimide molecular chains were more tightly packed, leading to a smaller free volume and lower molecular chain mobility. These properties are not conducive to the permeation of small molecules into the film; thus, the gas barrier properties were improved. The findings have significant implications for the structural design of high-barrier materials and could promote the development of flexible display technology.
本研究设计并合成了一种间位酰胺取代的二苯胺单体（m-DABA），它是之前研究过的对位酰胺取代二苯胺单体DABA的立体异构体。这种新单体与均苯四甲酸二酐（PMDA）聚合，采用与之前研究类似的方法制备了聚酰亚胺薄膜（m-DABPI）。通过分子模拟、广角X射线衍射（WXRD）和正电子湮没寿命谱（PALS）研究了单体上取代位置与聚酰亚胺薄膜气体阻隔性能之间的关系，以更深入地了解气体阻隔机理。结果表明，与对位取代的DABPI相比，m-DABPI表现出更好的气体阻隔性能，其水蒸气透过率（WVTR）和氧气透过率（OTR）分别低至2.8 g·m⁻²·d⁻¹和3.3 cm³·m⁻²·d⁻¹。这是因为间位连接的聚酰亚胺分子链堆积更紧密，导致自由体积更小，分子链迁移率更低。这些特性不利于小分子渗透到薄膜中；因此，气体阻隔性能得到了改善。这些发现对高阻隔材料的结构设计具有重要意义，并可能推动柔性显示技术的发展。
