Synthesis of novel highly heat-resistant fluorinated silane coupling agents

Novel fluorinated silane coupling agents with a biphenyl structure, CnF2n+1(C6H4)2CH2CH2Si(OCH3)3 (n = 4, 6, and 8), were synthesized with the aim to improve the heat-resistance, oxidation-resistance, and acid-resistance of the surface modified with a common fluorinated silane coupling agent. Alcohols, Rf(C6H4)2CH(OH)CH3, were obtained by reducing the intermediates, Rf(C6H4)2COCH3, the products of the reaction of 4-acetyl-4′-bromobiphenyl with perfluoroalkyl iodides in the presence of copper powder. The reaction of the alcohols with phosphorus tribromide gave olefins, Rf(C6H4)2CHCH2, which were then allowed to react with tetramethoxysilane in the presence of hexachloroplatinate(IV) catalyst to yield novel fluorinated silane coupling agents with a biphenyl structure. The coupling agents with four and six carbon atoms in their fluorocarbon chains were obtained as a colorless liquid while that with 8 carbon atoms was a white gel. Evaluations were made of the coupling agents using surfaces modified with them in terms of water contact angles, heat-resistance, oxidation-resistance, and acid-resistance. The agents behaved similarly to the conventional fluorinated silane coupling agents with respect to water contact angles, oxidation-resistance, and acid-resistance, whereas the former showed an extremely higher heat-resistance (up to 350 °C). In addition, C6H5C6H4CH2CH2Si(OCH3)3 and CH3(C6H4)2CH2CH2Si(OCH3)3 with no fluoroalkyl group were synthesized and the heat-resistance of glass surfaces modified with these compounds was examined.

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