SILICON-ASSISTED ETHERIFICATION REACTIONS - APPLICATION TO THE SYNTHESIS OF HIGH-MOLECULAR-WEIGHT POLYETHERS

The formation of ether bonds by reaction of benzylic bromides with phe nyl silyl ethers has been investigated as an alternative to the classi cal Williamson ether synthesis. The reaction has been applied to the s ynthesis of high-molecular-weight polyethers that are not readily obta ined by other methods. An AB-type monomer, such as 3-bromomethyl-trime thylsilyloxybenzene, reacts in the presence of a stoichiometric amount of carbonate to afford the corresponding polyether with molecular wei ght as high as 300000 depending on the reaction conditions. While the polyetherification reaction of 3-bromomethyl phenol under classical co nditions leads to polymers rich in C-alkylated and branched units, con ditions may be found to reduce or prevent C-alkylation and branching w ith 3-bromomethyl-trimethylsilyloxybenzene. The reaction is believed t o proceed via activation of the O-Si bond through carbonate addition t o afford a species containing a pentacoordinate silicon. The role of c arbonate and the stoichiometry and mechanism of the reaction have been investigated with the help of a model etherification reaction.