Optimization of mechanical and dielectric properties of poly(urethane–urea)-based dielectric elastomers via the control of microstructure

In this work, we fabricated novel poly(urethane–urea) (PUU)-based dielectric elastomers using a hydroxyl-terminated butadiene–acrylonitrile copolymer (HTBN) as the soft segment and hexamethylene diisocyanate (HDI) and 3,3′-dimethyl-4,4′-diamino dicyclohexyl methane (DMDC) as hard segments. The effect of hard segment (HS) content on the hard domain (HD) structure, morphology, dielectric and mechanical properties was investigated with Fourier transform infrared spectroscopy (FTIR), small/wide angle X-ray scattering (SAXS/WAXS), broadband dielectric spectroscopy and mechanical testing methods. Our results indicated that the hard domain structure units of PUUs such as degree of hydrogen bonding, size and crystallinity played an important role in the dielectric and mechanical properties. The dielectric constant of PUUs was significantly decreased with increasing HS content, whereas the breakdown strength and Young's modulus of PUUs were significantly increased. The relationship between multi-length scale structure and dielectric constant and breakdown strength properties of PUUEs were discussed. Our results can provide a new insight for optimization of dielectric and mechanical properties of PUU-based dielectric elastomers.