Partially bio-based triarylamine-containing polyimides: Synthesis, characterization and evaluation in non-volatile memory device applications

Abstract

A new triarylamine-containing diamine, viz. 4, 4′-diamino-4″pentadecyltriphenylamine was synthesised starting from cashew nut shell liquid (CNSL) - a non-edible by-product of cashew processing industry. Three new partially bio-based triarylamine-containing polyimides were synthesised by one-step high temperature solution polycondensation of 4, 4′-diamino-4′'pentadecyltriphenylamine with aromatic dianhydrides, namely, 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6-FDA). Polyimides were determined to be of reasonably high molecular weights as inherent viscosity and number average molecular weights (Mn, Polystyrene standard) values were in the range 0.54–0.60 dL g−1 and 26,800–43,500 g mol−1, respectively. Polyimides exhibited excellent solubility in common organic solvents and film-forming nature along with reasonably good thermal properties as indicated by temperature for 10% weight loss (T10) and glass transition temperatures (Tg) which were in the range 418–447 and 165–225 °C, respectively. The optical and electrochemical band-gap values were in the range of 1.95–1.98 eV and 1.671–1.745 eV, respectively. Among triarylamine-containing polyimide devices, BPDA-based device showed acceptable current-voltage and non-volatile memory properties such as the endurance of 500 cycles and 1000 s of retention time. The conduction mechanism developed in the memory devices was also explored and was found to follow Ohmic and Schottky conduction mechanisms.