Ferroelectric Polarization Reversal Stabilized by Hydrogen Bonding in N-Phenylated Aromatic Polyurea

Abstract

KEY WORDSPolyurea / Ferroelectricity / Hydrogen Bonding / Remanent Polarization / Pyroelectricity / Recently, Polyureas are attracting much attention in the fields of electronics and photonics. Polyureas with large dipole moments (4.5D) of -NHCONH show strong pyroelectric 1 and ferroelectric behavior. 2 The molecules in most polyureas are generally aggregated by a strong hydrogen bonding of NH· · 0 = C to induce unusual properties. It is of great interest to study the roles of hydrogen bonding in connection with electrical properties.The N-phenylated aromatic polyurea used in this study, synthesized by reacting an equimolar mixture of diamino-p-xylene with 4,4'-diphenylmethane diisocyanate, forms flexible and transparent films and exhibits a large second-order nonlinear optical coefficient after poling. 3 • 4 These properties seem to arise from the chemical structures of polymers. The lower density of hydrogen bonding introduced by N-substituted structure and bulky main chain are responsible for an amorphous structure. Though it is easy to form polar structures of polymers with hydrogen bonding, not to realize a ferroelectric structure. However, if one polymer chain can obtain a polar chain structure without an strong aggregate moiety such as hydrogen bonding, the resulting bulk structure would be ferroelectrics by controling the external electric field.This communication discusses the possibility of amorphous ferroelectrics for polyurea systems having a small amount of hydrogen bonding.Polyurea prepared by the method as described earlier 3 was cast into thin film (5 µm) from a chloroform solution at room temperature. Thin film samples metalized by aluminum evaporation on both sides were subjected to the polarization reversal measurement. Dielectric measurements were carried out under vacuum with a HP 4285 LCR meter. Displacement-field (D-E) curves were generated from the I-V data obtained by measuring the current through the electrode area in response to a triangular voltage input with a frequency of 0.01 Hz. Thermally stimulated depolarization current (TSC) for poled samples was recorded at a heating rate of 4°C min -1 . IR spectra for the polyurea film were recorded on a JASCO FT/IR3 spectrometer.Dielectric measurement performed on thin 505

Solvent-Free Design of Biobased Non-isocyanate Polyurethanes with Ferroelectric Properties

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“… 17 A strategy was also used to obtain ferroelectric switching in some amorphous aromatic PUs, for which P–E hysteresis loops similar to those reported here were found. 20 , 23 Therefore, it is important to discuss about the shape and the possible origin of the switching observed in the current loops of these samples to discard the artificial polarizations coming from charge accumulation at interfaces.…”

“…Therefore, other types of polymers have been extensively investigated in the last decade and significant efforts are more and more being focused on sustainable and environmentally friendly ferroelectric polymers. Among them, polyurethanes (PUs) represent the most versatile polymers nowadays. ,− They are the sixth most widely used polymers being applied in many industrial fields with a variety of physical, chemical, and interesting electroactive properties. The structural and ferroelectric properties of aliphatic PUs were first reported by Tasaka et al, and it was suggested that ferroelectricity was originated from the hydrogen-bonded crystalline regions.…”

Ferroelectric Polymers and Their Energy‐Related Applications

“…It is the urea bonds in polyureas that lead to the formation of intermolecular hydrogen bonds, and hence make polyureas analogous to nylons in the mechanism behind their piezo‐ and ferroelectric behaviors. Ferroelectric polarization reversal was first observed in polyureas in the early 1990s . For example, a well‐defined D – E hysteresis loop was obtained from polyurea‐9 (an aliphatic polyurea with 9 carbon atoms in every repeating unit) at 30 °C under an external field of 50 MV m −1 .…”

Microscopic Mechanism of the Large Electrocaloric Effect in Vinylidene Difluoride-Based Polymers

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