Butyl/ether hybrid-terminated polysiloxanes for high-performance UV-curable polyurethanes: Ultra-low dielectric constant and superhydrophobicity in electronic packaging

To address the limitations of conventional polyurethane (PU) in electronic packaging (e.g., poor hydrophobicity, dielectric properties, and thermal stability), three mono-dihydroxyalkyl-terminated polysiloxanes (TMPME-PDMS, M NMR  = 995–3318 g/mol) featuring a butyl/ether hybrid terminal structure were synthesized via hydrosilylation and chemically grafted into acrylate-end-capped PU. The resulting silicone-modified polyurethane acrylates (Si-PUAs) were UV-cured with a 3 wt% photoinitiator (HMPA/HCHMP = 1:1). Relative to pure PUA, the hydrophobicity and thermal stability were significantly enhanced, together with reduced dielectric properties. With a mere 1 wt% TMPME-PDMS ( M NMR  = 3318 g/mol), the water contact angle was increased from 79.34° of pristine PU to 118.09°. When incorporating 10 wt% TMPME-PDMS ( M NMR  = 2218 g/mol), the soft-segment decomposition temperature ( T gs) was elevated to 412.60 °C, which was 19.20 °C higher than unmodified PU. At 14.2 GHz, 10 wt% TMPME-PDMS ( M NMR  = 3318 g/mol) reduced the dielectric constant to 2.67, 6.32 % lower than PU. The molecular weight ( M NMR ) and dosage of TMPME-PDMS critically governed microphase separation, crosslinking density, and surface migration, enabling tunable performance. This work provides a scalable strategy for high-performance UV-curable coatings in advanced electronics packaging.