The investigation of conduction current characteristics of segmented PU elastomers

Polyurethane elastomers (PUs) are a class of multi-phase copolymers commonly composed of polyester or polyether soft segments and urethane hard segments. Microphase separation caused by the thermodynamic incompatibility of the soft segments and the hard segments is believed as the structural basis for many unique properties of PUs, such as shape memory and self-healing. PU is one of the most promising polymers to develop into a new generation of smart self-healing polymer dielectrics due to its shape memory effect and tailor characteristics. Conduction current is not only a basic parameter of dielectrics, but also can reflect many microscopic characteristics of the carrier transport process, which is widely used to investigate the electrical behavior of dielectric materials. The aim of this paper is to report on the conduction current characteristics of segmented PUs.
PUs with 50% hard segment content were synthesized with polyether polyol, 4, 4-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO) by a two-step method. The hydrogen bonding interaction of the microphase separation interface is evaluated by the deconvolution of the FT-IR spectra in the carbonyl stretching regions and the amino stretching regions. The charging and discharging behavior of the PU under the applied electrical field strength from 0.2 kV/mm to 1.4 kV/mm is investigated. The results shows that the unique microphase separation structure of PU is a significant reason of interface polarization, leading to an increase in its transient current, which is different from the continuous decay trend of transient currents in most other polymer dielectrics. Meanwhile, when the applied electrical field strength is greater than 1 kV/mm, the measured conduction current is affected by space charge injection, and the discharging current curve shows an increasing peak of heteropolar charge.