Material Design and Structure–Property Relationship of Low- <i>k</i> Fluorosilicone Modified Polyimide Films

To elucidate the structure–property relationships governing low-dielectric-constant (low- k ) polyimide (PI) materials, this study focuses on molecular design and synthesis, preparing a series of α, ω-bis(aminopropyldimethylsiloxane)-terminated poly(dimethylsiloxane-co-methyltrifluoropropylsiloxane) (PFMS) flexible segments. By adjusting the fluorine content and molecular weight, these oligomers were copolymerized into a PMDA/ODA-type PI backbone, yielding fluorosilicone-modified PI (PI–PFMS) films. The influence of PFMS structural parameters on microphase-separated morphology and on the resulting thermal, mechanical, and dielectric behavior was systematically investigated. The results demonstrate that incorporating PFMS induces microphase separation, resulting in a characteristic “sea–island” morphology. A pronounced synergistic effect is observed between the siloxane segments and the fluorine atoms: the electronegative fluorine atoms reduce the electronic polarizability, while the flexible Si–O–Si linkages augment the free volume. Consequently, the dielectric constant of the modified PI is systematically tuned, decreasing from 3.5 for pristine PI to 2.24 at 10 MHz. Notably, this work highlights the intrinsic trade-off in material design─namely, that a reduction in dielectric constant is inevitably accompanied by changes in tensile strength and optical transmittance, attributable to thermodynamic incompatibility and phase separation. This study offers fresh insights into the synergistic optimization mechanism of fluorine/silicon comodification and provides a new pathway for the design of advanced polyimide dielectrics.