Influence of Soft Segment Length on the Dielectric Polarization Behavior of Ketal-containing Polyurethane Elastomer

Abstract

Polyurethane elastomers exhibit high dielectric constants owing to their polar groups, and can be used as energy storage capacitors. Energy storage depends not only on the dielectric constant but also on the dielectric loss. However, the relationship between chain structure and dielectric properties is not yet clear. Ketal-containing crosslinked polyurethane elastomers were prepared using cyclic ketal diol as a chain extender. The effect of the soft segment length on the dielectric properties and energy storage was investigated. The cause of the change in the dipolar polarization with the soft segment length was analyzed. As the soft segment length increased, the hard-soft hydrogen bonding decreased, whereas the hard-hard hydrogen bonding increased. Under the action of an electric field, the polar bonds in the ketal-containing polyurethane elastomer overcome the hydrogen bonding between hard-soft segments to produce polarization; meanwhile, they also experience crankshaft motions to generate polarization. The former has a relatively high relaxation activation energy of approximately 10–20 kJ·mol−1, resulting in a large dielectric loss. The latter has a relatively low relaxation activation energy, approximately 0.7–1.7 kJ·mol−1, leading to low dielectric loss. As a result, the dielectric constant showed a decreasing trend, and the dielectric loss gradually decreased. This study provides a theoretical foundation for improving the dielectric properties of polyurethane elastomers.