Synthesis of acetylene-functionalized [2]rotaxane monomers directed toward side chain-type polyrotaxanes

Abstract

A crown ether–ammonium salt-type rotaxane monomer was synthesized in a high yield using dibenzo-24-crown-8-ether and sec-ammonium salt having a hydroxy terminal by means of an end-capping reaction with an ethynyl benzoic acid. Its N-acetylated derivative was also synthesized in a quantitative yield using excess acetic anhydride and triethylamine. Novel side chain-type polyrotaxanes, that is, ammonium-type and neutral polyphenylacetylenes tethering rotaxane moieties in side chains with high molecular weights, were obtained in high yields by polymerizations with an Rh catalyst. The structures of the polymers were characterized by infrared, ultraviolet-visible (UV-vis) spectra and size exclusion chromatography. N-acetylation of the rotaxane moieties of the ammonium salt-type polymer resulted in the formation of a reddish-colored neutral polymer showing red-shifted UV-vis absorptions around 500 nm based on the conjugated main chain, according to the structural change of rotaxane side chains, that is, the change of the distance of the wheel component to the polyacetylene main chain. The solubility of the polymers was evaluated. A crown ether–ammonium salt-type rotaxane monomer was synthesized in a high yield using dibenzo-24-crown-8-ether and sec-ammonium salt having a hydroxy terminal by means of an end-capping reaction with an ethynyl benzoic acid. Its N-acetylated derivative was also synthesized as a neutral monomer. Novel side chain-type polyrotaxanes, that is, ammonium-type and neutral polyphenylacetylenes tethering rotaxane moieties in side chains with high molecular weights were obtained in high yields by polymerizations with an Rh catalyst. N-acetylation of the rotaxane moieties of the ammonium salt-type polymer afforded a red-colored neutral polymer showing red-shifted UV-vis absorption due to the conjugated main chain, according to the change in distance between the wheel component and the polyacetylene main chain.