Synthesis of a Novel Rigid Semi-Alicyclic Dianhydride and Its Copolymerized Transparent Polyimide Films' Properties

A new series of colorless polyimides (CPIs) with outstanding thermal properties and mechanical properties were fabricated by the copolymerization of a novel dianhydride and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 2,2′-bistrifluoromethyl benzidine (TFDB). The novel dianhydride, 10-oxo-9-phenyl-9-(trifluoromethyl)-9,10-dihydroanthracene-2,3,6,7-tetraacid dianhydride (3FPODA), possessed a rigid semi-alicyclic structure, –CF₃ and phenyl side groups, and an active carbonyl group. Benefitting from the special structure of 3FPODA, the glass transition temperatures (T_g) of the new CPIs improved from 330 °C to 377 °C, the coefficient of thermal expansion (CTE) decreased from 46 ppm/K to 24 ppm/K, and the tensile strength (T_S), tensile modulus (T_M), and elongation at break (E_B) increased from 84 MPa to 136 MPa, 3.2 GPa to 4.4 GPa, and 2.94% to 4.13% with the increasing amount of 3FPODA, respectively. Moreover, the active carbonyl group of the 3FPODA could enhance the CPI’s adhesive properties. These results render the new dianhydride 3FPODA an ideal candidate monomer for the fabrication of high-performance CPIs.

Regulating the electrical resistive switching behaviors of polyimides through different steric hindrance substituents on 2,7-position of tetraphenyl fluorene diamines moieties

Three novel polyimides (PI(TPF-Br BPDA), PI(TPF-Ph BPDA), and PI(TPF-Ph-OMe BPDA)) with tetraphenyl fluorene (TPF) were synthesized and tested. The laboratorial results showed that the constructed electronic devices exhibited different memory behaviors due to the different steric hindrance substituents (bromine atom, phenyl, and 3,5-dimethoxyphenyl) in 2,7-position of TPF molecule. The memorizers based on PI(TPF-Br BPDA) and PI(TPF-Ph BPDA) presented volatile dynamic random access memory (DRAM) feature with turn-on voltages of −2.39 and +1.45 V, as same as −1.71 and +1.74 V, separately. However, the PI(TPF-Ph-OMe BPDA) based apparatus exhibited non-volatile write-once read-many-times memory (WORM) behavior with turn-on voltage of −1.13 V, due to the more charge traps of 3,5-dimethoxyphenyl moieties and higher dipole moment. The switching mechanism was verified by quantum simulation of energy level, electrostatic potential (ESP) surface and dipole moment. These results indicated that the electrical memory performance of the synthesized TPF-based PIs could be adjusted by modifying the electron donor structure.

Effect of a "Zn Bridge" on the Consecutively Tunable Retention Characteristics of Volatile Random Access Memory Materials

Polyimide memory materials with a donor-acceptor structure based on a charge-transfer mechanism exhibit great potential for next-generation information storage technology due to their outstanding high-temperature resistance and good dimensional and chemical stability. Precisely controlling memory performance by limited chemical decoration is one of core challenges in this field. Most reported work mainly focuses on designing novel and elaborate electron donors or acceptors for the expected memory behavior of polyimides; this takes a lot of time and is not always efficacious. Herein, we report a series of porphyrinated copolyimides coPI-Znx (x=5, 10, 20, 50, 80), where x represents the mole percentage of Zn ion in the central core of the porphyrin. Experimental and theoretical analysis indicate that the Zn ion could play a vital bridge role in promoting the formation and stabilization of a charge-transfer complex by enhancing the hybridization of local and charge transfer (HLCT) excitations of porphyrinated polyimides, endowing coPI-Znx with volatile random access memory performance and continuously tunable retention time. This work could provide one simple strategy to precisely regulate memory performance merely by altering the metal content in porphyrinated polyimides.

Novel carbazole-based donor-isoindolo[2,1-a]benzimidazol-11-one acceptor polymers for ternary flash memory and light-emission

Three novel donor-acceptor polymers (PCz0, PCz2 and PCz4) based on 9-(9-heptadecanyl)-9H-carbazole and isoindolo[2,1-a]benzimidazol-11-one with fluorine substituents (0, 2 and 4) on the acceptor unit were prepared by Suzuki polymerization. The synthesized polymers were studied by theoretical calculation, and optical and electrochemical characterizations to further investigate the performance of memory storage and light-emission. The memory devices of the three polymers all exhibited obvious ternary flash behavior with total ON/OFF state current ratio around 104 and threshold voltages below 3.0 V, with no other blending or doping. Bright emissions of an electroluminescence device based on PCz0 was obtained at 556 nm, the maximum brightness was 2006 cd m-2 with EQE of 0.21%. The results suggested that polymers with the structure of carbazole-based donor as backbone and isoindolo[2,1-a]benzimidazol-11-one segment as acceptor could be excellent materials for memory storage and light-emitting applications with further investigation and could be used for further design of other new polymer systems.