Preparation and Characterization of High‐Dielectric‐Performance Polyurethane Based on Various Diisocyanates

ABSTRACT Enhancing the dielectric properties of polymer materials plays a crucial role in reducing the volume, weight, and cost of dielectric capacitors. In this work, polyurethanes (PUs) for high dielectric performance were fabricated using poly(tetramethylene ether glycol) (PTMG) and polycarbonate diol (PCDL) as soft segments and hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4′‐diphenylmethane diisocyanate (MDI), and toluene diisocyanate (TDI) as hard segment components. The effects of the type and chemical structure of diisocyanate on the microphase separation, crystallization, dielectric properties, and mechanical properties of PUs were investigated. Within the frequency range of 10 −1 –10 5 Hz, MDI‐PU exhibited the lowest conductivity (7.32 × 10 −9 S·m at 10 −1 Hz) and the smallest dielectric loss (0.014 at 10 3 Hz), demonstrating excellent insulation properties. This was because the aromatic hard segments of MDI were more rigid, resulting in a tighter molecular arrangement, which facilitates the reduction of polarization loss and charge migration. In addition, the crystallinity and dielectric constant of HDI‐PU were higher than those of IPDI‐PU, MDI‐PU, and TDI‐PU. This study demonstrates the deep influence of different diisocyanates on the properties of polyurethanes, revealing the importance of hard‐segment structure, crystallinity, and polarization processes in modulating the dielectric properties.