Morphology-Dependent Electrical Memory Characteristics of a Well-Defined Brush Polymer Bearing Oxadiazole-Based Mesogens

A new oxadiazole-containing brush polymer, poly(5-phenyl-1,3,4-oxadiazol-2-yl-[1,1'-biphenyl]carboxyloxy- n-nonyl acrylate) (PPOXBPA), was synthesized. The polymer was thermally stable up to 350 degrees C. Below the degradation temperature, it showed a glass transition, crystal melting transition, and a liquid crystal to isotropic melt transition. Its optical and electrochemical properties were also investigated. This brush polymer was found to always self-assemble into a multibilayer structure, with partial interdigitation between bristles from different layers occurring via the pi-pi stacking of the oxadiazole mesogen units. Interestingly, when the polymer film was applied in devices with a bottom and top electrode, it showed either volatile or nonvolatile memory behavior, depending on the ordering and orientation of the multibilayer structure (particularly, the pi-pi stacked oxadiazole mesogen units), which could be controlled via thermal annealing. The switching mechanisms of these electrical memory behaviors were investigated. Collectively, these results demonstrate that this chemically well-defined brush polymer is suitable for use as an active material for the low-cost, mass production of high-performance, programmable volatile and nonvolatile memory devices via control of the morphological structure.