Preparation And Properties Of Polyimide Films Modified By Poss For Flexible Electronic Devices

Polyimide（PI）is a type of polymer material formed by the polymerization of diamine and dianhydride monomers.There are various forms of PI,among which membrane is the most commonly used ones.PI film has excellent properties such as high strength,toughness,abrasion resistance,and high temperature resistance,making it an important raw material for many industries.Electronic grade PI film stands out from many polymer materials due to its excellent comprehensive performance.It acts as a suitable substrate and cover material in the field of optoelectronic devices.Nowadays,there remain a lot of research space for performance optimization of electronic grade PI film.Due to the special molecule structure of PI,charge transfer complex（CTC）that absorbs light is generated in the molecule,which causes yellow-brown in film color and great restriction in their application of flexible displays.The commonly used modification method is to adjust the molecular structure of the synthesized monomers diamine and dianhydride to avoid the formation of a large number of rigid conjugated structures,thereby suppressing the formation of CTC and achieving the goal of improving optical transmittance.However,the inherent advantages of PI in thermal stability and dimensional stability are weakened.There are certain conflicts between the optimization principles of different properties of PI,which adds difficulties to the preparation of PI with more excellent comprehensive performance,thus limiting the application scope of electronic grade PI film in flexible electronic devices.Therefore,balancing all properties of PI,which means achieving optimization of certain properties while maintaining other excellent properties is a problem worthy of further research.Polyhedral oligomeric silsesquioxane（POSS）is a nano scale siloxane material composed of an inorganic core with Si-O-Si bonds and organic functional groups attached to the silicon atoms in the vertices.The molecular structure is stable,with low density and light weight,and is not easy to shrink or deform.POSS has excellent heat resistance,chemical stability,high modulus,and high transparency.The advantages of POSS in properties are well-matched to the application requirements of PI.More and more research on PI modification has therefore begun to focus on POSS/PI composite systems.This work focuses on PI film materials applied in flexible electronic devices,introducing POSS into PI molecules in a chemically hybridized manner to explore the influence of POSS hybrid modification on the optical,thermal,and electrical properties and other basic properties of PI films.The details of the work are listed as follows:1.A suitable synthesis path was developed for POSS monomers and the target monomers were prepared:BPOSS-NH₂for PI molecular chain end capping,and DDPOSS-2NH₂for PI molecular chain modification.The structures and high purity of both monomers were verified by¹H NMR.2.In terms of the synthesis of PI,the chemical imidization method of the two-step method was used to prepare PI,wich was hybridized with the two kinds of POSS monomers in a chemically hybridized manner.The hybridization method is specific as follows:using BPOSS-NH₂for capping modification of the PI molecular chain end and introducing DDPOSS-2NH₂into the PI main chain.A series of hybrid PI films with different POSS contents were prepared by changing the content of the POSS monomer in each hybridization method.BPOSS-NH₂,DDPOSS-2NH₂,and PI were successfully hybridized,as verified by ¹H NMR and ATR-FTIR.3.Compared with pure PI films,the transmittance at 400 nm of end-capping POSS-PI hybrid films and mainchain modified POSS-PI hybrid films increased by 72.7%and 114%,respectively.The dielectric constants at a frequency of 10²Hz decreased by 15%and 20%,respectively.The hydrophobicity of both types of hybrid PI films was improved.At the same time,the two types of hybrid PI films maintained the same level of thermal and dimensional stability performance as the original PI.