Tuning memory behavior from volatile to nonvolatile by increasing the linear segment length of hyperbranched copolyimides

In this work, three donor-acceptor contained hyperbranched copolyimides (O30-coPI, O50-coPI and O70-coPI) with different linear segment length were synthesized by varying the feed ratio of monomers . The memory device based on O30-coPI showed an unstable volatile static random access memory (SRAM) behavior, while the devices based on O50-coPI and O70-coPI with longer linear segment exhibited stable non-volatile write once read many times memory (WORM) behavior. Theoretical simulations based on density functional theory (DFT) showed that the linear segment induce a twisted conformation, which helps to stabilize the charge-separation state. As the linear segment grows, the conformation becomes more distorted, resulting in a more stable charge-separated state. Compared to O30-coPI, O50-coPI and O70-coPI have longer linear segment and more twisted conformations, thus they exhibit non-volatile memory behavior. This work demonstrates that the memory behavior can be controlled by changing the linear segment length of HB-coPI, providing a practicable strategy for the design of polymer memory materials.