State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
Changzhou Institute of Advanced Materials, Beijing University of Chemical Technology, Changzhou 213164 Jiangsu, China.
J Phys Chem B. 2020 Sep 10;124(36):7969-7978. doi: 10.1021/acs.jpcb.0c05146. Epub 2020 Aug 28.
Pre-imidization has been found to have a determining role on the final properties of polyimide (PI) films. In this work, a series of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA)/2,2'-bis(trifluoromethyl)benzidine (TFMB) PI models with specified pre-imidization degree (pre-ID) were constructed and analyzed on the basis of molecular dynamic (MD) simulation to reveal the real-time evolution of structure and properties that occurred during the pre-imidization process. The MD results indicated that the of the models increased obviously with increasing pre-ID, which corresponded to the increase of rigid PI chain segments that restricted the mobility of molecular chains. In addition, the increase of fractional free volume and mean square end-to-end distance indicated looser chain packing and more extended chain conformation during the pre-imidization process. As a further verification, a series of corresponding PI films were experimentally prepared via a controlled partially pre-imidization process. Mechanical properties of the prepared PI films were tested to be significantly enhanced, and the coefficient of thermal expansion decreased from 61.5 to 47.6 ppm/°C with pre-ID increasing from 0% to 100%, which could be attributed to the orderly molecular chain arrangement formed during the chemical pre-imidization process, as disclosed by MD simulation. This work paves the way for the observation of the real-time structure and property evolutions of PI materials, especially during the pre-imidization process.
预亚胺化被发现对聚酰亚胺（PI）薄膜的最终性能起着决定性的作用。在这项工作中，基于分子动力学（MD）模拟，构建了一系列具有特定预亚胺化度（预-ID）的 4,4'-(六氟异丙基)二邻苯二甲酸酐（6FDA）/2,2'-双（三氟甲基）联苯（TFMB）PI 模型，以揭示预亚胺化过程中结构和性能的实时演变。MD 结果表明，随着预-ID 的增加，模型的 增加明显，这对应于刚性 PI 链段的增加，这些刚性 PI 链段限制了分子链的迁移性。此外，分数自由体积和均方末端到末端距离的增加表明，在预亚胺化过程中，链的堆积更加松散，链构象更加伸展。作为进一步的验证，通过控制部分预亚胺化过程，实验制备了一系列相应的 PI 薄膜。所制备的 PI 薄膜的力学性能显著增强，热膨胀系数从 61.5 降至 47.6 ppm/℃，预-ID 从 0%增加到 100%，这归因于 MD 模拟揭示的化学预亚胺化过程中形成的有序分子链排列。这项工作为观察 PI 材料的实时结构和性能演变铺平了道路，特别是在预亚胺化过程中。
