Preparation And Properties Of Hyperbranched Polyimide Electrical Storage Materials

Recently,functionalized polyimide has a wide application prospect in the field of polymeric electrical storage materials due to its excellent thermal stability,excellent mechanical strength,oxidation resistance,and corrosion resistance.So far,there have been many reports on the storage performance of functionalized polyimides.However,these reports are mainly based on linear polyimides,and there are few reports on the storage performance of hyperbranched polyimides.Although linear polyimide has excellent performance in storage and has a good application prospect,it also has certain disadvantages.The backbone of functionalized linear polyimide usually contains a large number of conjugated groups,which in turn greatly reduces the flexibility of the molecular chains because the introduction of conjugated groups often causes ?-? dense packing.Usually the solubility of the materials will become poor and the corresponding processing performance will not be very good.Meanwhile,the modification of the linear polyimide can only be achieved through the design of the monomer and the change of the main chain structure,and it is difficult to modify through graft or capping.In comparison,hyperbranched polyimides always have a low viscosity and high solubility,due to their unique three-dimensional spherical highly branched structure,which are advantageous for the preparation of memory devices.At the same time,the modification of the hyperbranched polyimide is no longer limited to the adjustment of the main chain structure.The hyperbranched polyimide can be modified by designing functionalized end groups to adjust the storage performance.Concerning of advantages of hyperbranched polyimides,we explored the impact of hyperbranched structures on storage performance in this paper.We also modified the hyperbranched polyimides in the main chain and the end groups to adjust the storage performance.First,a hyperbranched polyimide TPA-6FHBPI was prepared via condensation polymerization of tris(4-aminophenyl)amine as an electron donor with a commercial dianhydride,6FDA.And an ITO/TPA-6FHBPI/Al sandwich structure memory device based on this polymer was fabricated.The performance of this device was studied.The effect of hyperbranched structure on the memory performance was explored by means of molecular simulation and by comparison with the previously reported linear TP6FPI;A new triamine monmer,tris(4-(2-(4-aminophenyl)ethynyl)phenyl)amine(TAEPA)was designed and synthesized.A novel hyperbranched polyimide TAEPA-6FHBPI was obtained via condensation polymerization of this triamine as electron donor with 6FDA.A ITO/TAEPA-6FHBPI/Al sandwich memory device based on this polymer was fabricated,the performance of the device was also studied.Through molecular simulation and comparison with TPA-6FHBPI-based devices,we explored what impact the introduction of large conjugated groups in the main chain of hyperbranched polyimides has on the memory performance.Second,two kinds of capping monomers containing azo group and carbazole group respectively were designed and synthesized.The TPA-6FHBPI was modified by end capping to obtain two novel hyperbranched polyimide TPA-6FHBPI-AZO and TPA-6FHBPI-OCZ.Two polymers based on ITO/polymer/Al sandwich structure were prepared.The properties of the device were studied.The effects of functionalized end groups on the storage properties of hyperbranched polyimides were explored.Due to the conjugated structure of azobenzene,the efficiency of polymer charge transfer is increased,the formation of charge transfer complexes is promoted,thus the threshold voltage of the memory device is greatly reduced;the azobenzene group with nitro group is also used as the charge traps,limiting the recovery of charge and stabilizing the charge-transfer complex.Therefore,TPA-6FHBPI-AZO is no longer a volatile storage activity,but exhibits a non-volatile WORM-type storage property.TPA-6FHBPI-OCZ,which ended with a carbazole group containing a flexible chain,exhibits ternary storage properties because the carbazole group of the flexible chain undergoes a conformational change under an electric field,forming a face-to-face conformation.The conformation provides a channel for the charge carrier transport and can further bring about a sudden change in conductivity,thus the device based on TPA-6FHBPI-OCZ exhibits a volatile tristable memory property.