Achieving Relaxor Ferroelectric-like Behavior in Nylon Random Copolymers and Terpolymers

High dielectric constant polymers, exhibiting relaxor ferroelectric (RFE) behaviors (i.e., slim single and double hysteresis loops, SHLs and DHLs), are attractive for high energy density and low loss dielectric applications. Utilizing the principle of nanosized ferroelectric domains (nanodomains), this study has designed and developed novel RFE-like polyamides (PAs) based on 11-aminoundecanoic acid, 12-aminododecanoic acid, and N-methyl-11-amino-undecanoic acid (NM11) as an alternative to the high-cost and difficult-to-synthesize poly(vinylidene fluoride) (PVDF)based RFE polymers. In the first attempt, quenched and stretched (QS) PA(11-co-12) copolymers exhibited enhanced ferroelectricity as compared with either nylon-11 or nylon-12. Although relatively narrow hysteresis loops could be achieved at 75 degrees C, the hydrogen-bonding interaction was not weak enough to induce nanodomains in the nylon copolymers. To further reduce the hydrogen-bonding interaction and achieve nanodomains, a PA(11-co-12-co-NM11) 30/60/10 (molar ratio) terpolymer (terPA-NCH3) was synthesized. The NCH3 groups were expected to participate in the isomorphic crystals, blocking the formation of hydrogen bonds and inducing chain twists in the mesophase. Indeed, the RFE-like behavior with slim SHLs and high dielectric constant (60-70) was successfully achieved for the QS terPA-NCH3 at high temperatures (>75 degrees C). Pathways to achieve RFE-like behavior for nylon-based polymers are discussed and compared with those for PVDF-based polymers. The knowledge obtained from this study can inspire potential applications for nylon polymers in advanced electrical and power applications.