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Organically bridged polysilsesquioxane (PSQ)‐based reverse osmosis (RO) membranes have been studied for water desalination. In this work, RO membranes were prepared from tris[3‐(triethoxysilyl)propyl]amine (TTESPA), tris[3‐(diethoxymethylsilyl)propyl]amine (TDEMSPA), tris[(triethoxysilyl)methyl]amine (TTESMA) tris[(triethoxysilyl)propenyl]amine (TTESP2A), and tris[3‐(triethoxysilyl)prop‐2‐ynyl]amine (TTESP3A) by the sol–gel process and interfacial polymerization. It was found that the TTESPA‐derived membranes gave the best RO performance among those prepared. The membrane prepared by the interfacial polymerization of TTESPA showed water permeance and salt rejection of 7.3 × 10−13 m3/m2sPa and 95.6% for 2000 ppm NaCl aqueous solution, respectively, which were higher than those previously reported for a membrane similarly prepared from bis[(triethoxysilyl)propyl]amine (1.4 × 10−13 m3/m2sPa and 93.6%).

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Copolymerization of bis [3-(triethoxysilyl)propyl]amine (BTESPA) and N-(2-hydroxyethyl)-N′- [3-(triethoxysilyl)propyl]urea (HE-TESPU) provided highly permeable robust reverse osmosis (RO) membranes that have an organically bridged polysilsesquioxane (PSQ) structure. The RO experiments with NaCl aqueous solution (2000 ppm) indicated that the introduction of hydroxyethylurea groups markedly improved the permeability of water (1.86 × 10 −12 m 3 /m 2 sPa) to approximately 19 times higher than that of a membrane prepared via the BTESPA homopolymerization, with NaCl rejection remaining nearly unchanged (96%). This is the highest water permeability obtained so far for PSQ-based membranes that show higher than 90% NaCl rejection. The improvement of water permeability is likely due to aggregation through hydrogen bonding in the PSQ layer, which can be regarded as a hydrophilic water channel.