Thermosensitive dielectric properties in polyamide–phenol hybrid compounds and their application to the temperature‐sensing wire

Thermosensitive dielectric properteis in polyamide–phenol hybrid compounds have been studied. The polyamide–phenol hybrid compounds are constituted of p ‐hydroxybenzoate–formaldehyde condensation oligomer dispersed molecularly in nylon 12 and polyamide copolymer. These materials are less hygroscopic than nylon 12 which is the least hygroscopic among polyamide homopolymers. It will be because the phenol group coordinates to amide group as the less hygroscopic “pseudo‐water” instead of water. One of these materials has also shown an intrinsic hydrophobic effect of hydrogen bond segment due to the “hybrid effect” between polyamide and phenol. The thermosensitive dielectric properties are based on the temperature dependence of intermolecular hydrogen bond behaviors by amide and phenol groups, which have been discussed in relation with the molecular behaviors. The relationship with polarizations constituting dielectric constant and hydrogen bonding molecular segments, and ac hopping conduction behaviors by proton carriers have also been discussed. These materials are applied as a temperature‐sensing material in a flexible thermosensing heater wire, which has three functions, that is, thermosensing, heating, and fusing for safe in the case of an abnormal overheat. As the features for a sensing material, these materials show the humidity low‐dependence and highly thermal stability, and will be situated as one of the high‐performance sensing material useful for the electric warmer such as an electric blanket.