Regulating the dielectric constant of UV-curable acrylate networks via double-Decker silsesquioxane functionalization for thin-film encapsulation

Solvent-free, UV-curable low-dielectric acrylate resins are attractive organic buffer layers for OLED thin-film encapsulation (TFE), but their dielectric response remains difficult to tune without compromising printability and film uniformity. Here, we develop printable acrylate networks by incorporating covalently polymerizable double-decker silsesquioxane (DDSQ) methacrylate monomers bearing long alkyl linkers. Di-functional DDSQ-2HMA and tetra-functional DDSQ-4HMA were synthesized and compared, with the cis/trans isomerism of DDSQ-2HMA further examined. The optimized tetra-functional formulation, DB-5%4HMA, achieved a dielectric constant (Dk) of 2.64 and a dielectric loss factor (Df) of 0.012 at 100 kHz, while retaining high optical transparency, a glass-transition temperature of approximately 130 °C, and sufficient thermal stability. Mechanistic analyses using PALS, WAXD, DMA, and DFT indicate that the dielectric reduction arises from the combined effects of low-polarizability Si–O–Si cage incorporation, reduced ester-rich segment concentration, improved microstructural uniformity, and modest local free-volume variation. The long alkyl linkers further suppress DDSQ aggregation and improve compatibility with the acrylate matrix. Importantly, DB-5%4HMA was processed by inkjet printing into continuous UV-cured coatings with TFE-relevant thickness and comparable dielectric performance. These results identify DDSQ-functionalized acrylate networks as promising printable low-Dk organic buffer layers for OLED TFE, while full water-vapor transmission rate and device-level encapsulation validation remain future work.