<p>With the development of flexible electronics and smart devices, the performance of high-dielectric polyurethane materials is more demanding, and an in-depth understanding of the relationship between their structure and dielectric properties is crucial for material design. In this work, a series of polyurethane materials with different hard segment content were synthesized, using poly(tetramethylene ether)glycol (PTMG) and poly(carbonate diol) (PCDL) as the soft segments, and 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO) as the hard segments. The effects of hard segment content on the microphase separation, mechanical properties, and dielectric properties of the polyurethane were systematically investigated. The results revealed that with increasing hard segment content, the degree of microphase separation, tensile strength, and dielectric constant of the polyurethane all increased. Among them, the sample with a hard segment content of 55% (PU-55%) exhibited the best overall performance and exhibited the most pronounced microphase separation, with a dielectric constant of 10.50 at 10²&#xa0;Hz and a tensile strength of 18.33&#xa0;MPa. In addition, it was found that N,N-dimethylformamide (DMF) produces dipole–dipole interactions with precursor molecules (MDI, PTMG, and PCDL) during the synthesis process, thereby modulating the polarity of the reaction environment. This work provides meaningful guidance for structure modulation and performance optimization of polyurethane materials.</p> Graphical abstract <p></p>