Synthesis and Solution Processing of Nylon-5 Ferroelectric Thin Films: The Renaissance of Odd-Nylons?

Among odd-nylons, nylon-5 exhibits the highest remanent polarization and is thus a desirable material for many applications of ferroelectric polymers. However, nylon-5 has never been used as a ferroelectric material, because the synthesis of nylon-5 and its processing into thin films are challenging. This work revisits the synthesis of nylon-5 via anionic ring opening polymerization (AROP) and studies the effect of reaction time and scale-up on (i) molecular weight (M_n), (ii) melting point (T_m), (iii) yield, and (iv) ferroelectric properties. For the first time, the molecular weight of nylon-5 is characterized via size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) spectroscopy, as well as matrix assisted laser desorption ionization time of flight mass spectroscopy (MALDI ToF-MS), showing M_n values of up to 12 500 g mol^-1. Extended reaction times and the synthesis on a larger scale increase the molecular weight and yield. Nylon-5 thin films are fabricated from a TFA:acetone (60:40 mol%) solvent mixture. Nylon-5 thin-film capacitors are ferroelectric and show a remanent polarization as high as 12.5 ± 0.5 μC cm^-2, which is stable in time. The high remanent polarization values, combined with the facile solution processing, render nylon-5 a promising candidate for future microelectronic and multi-ferroic applications.