Structural Evolution of Macromolecular Chain During Pre-imidization Process and Its Effects on Polyimide Film Properties

• Published in: The journal of physical chemistry. B 2020-09, Vol.124 (36), p.7969-7978
• Main Authors: Lin, Daolei, Liu, Yingzi, Jia, Ziqi, Qi, Shengli, Wu, Dezhen
• Format: Article
• Language: English
• Subjects: B: Fluid Interfaces, Colloids, Polymers, Soft Matter, Surfactants, and Glassy Materials
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/acs.jpcb.0c05146

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 T g 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.