Synthesis of organically bridged trialkoxysilanes bearing acetoxymethyl groups and applications to reverse osmosis membranes

New bridged trialkoxysilanes bearing acetoxymethyl groups were synthesized by double hydrosilylation of 1,6‐diacetoxy‐2,4‐butadiyne, using two equivalents of triethoxysilane and a metal catalyst. With a Ru catalyst, the reaction proceeded via anti‐addition to provide BTES‐Ac‐a as a single isomer, while a similar reaction with a Pt or Rh catalyst provided an isomeric mixture of syn ‐adducts BTES‐Ac‐b. Reverse osmosis (RO) silica membranes were prepared by the sol–gel process with BTES‐Ac‐a and BTES‐Ac‐b and the membranes were examined with respect to water desalination using a 2000 ppm NaCl aqueous solution. NaCl rejection of the membranes increased to reach 96% at the early stage of the RO experiments. However, the rejection decreased gradually to 85% after 70 and 200 h for BTES‐Ac‐a and BTES‐Ac‐b, respectively, due to hydrolytic decomposition of the silica network during the experiments. In contrast, a membrane prepared from copolymerization of BTES‐Ac‐a with ethane‐bridged bistrialkoxysilane (BTES‐E1) showed improved stability towards hydrolysis with stable NaCl rejection of 96% with higher water permeance (3.5 × 10 − 13 m 3 m − 2 s −1 Pa −1 ) than that of a membrane prepared by homopolymerization of BTES‐E1 (2.7 × 10 − 14 m 3 m − 2 s −1 Pa −1 ) reported previously.