A New Class of Polyconjugated Systems: Synthesis and Properties of Polymetacyclophanes

Abstract

A unique polyconjugated systems having longitudinal π-electron overlaps was synthesized by using a metacyclophane monomer, 8, 16-dihydroxy-[2,2]-metacyclophane. The monomer was synthesized according to Tashiro's method and was converted to two types of polycyclophanes. One was obtained as a quinoid-type polymer from FeCI₃ -catalyzed oxidative coupling of the 2,5-disubstituted phenols. The polymer obtained was composed of [2,2,] -metacyclophane units polymerized via a diphenoquinone linkage. Amorphous, bright reddish-orange powders were obtained quantitatively under mild reaction condition. Another one was a phenol-type polymer that contained [2,2] -metacyclophane units linked with a 4,4′-dihydroxybiphenyl skeleton. This polymer was obtained by way of a unique polycondensation reaction characteristic of cyclophane compounds. The polymer obtained had a fine whisker form with a golden luster and partial crystallinity. The structures of these polymers were confirmed by various spectroscopic methods and elemental analysis. The electrical conductivity of both polymers was of almost the same order of magnitude (10⁻⁸ S/cm). When doped with sulfuric acid (H₂SO₄) vapor, the phenol-type polymer exhibited a conductivity of 0.25 S/cm, which was much higher than that of the quinoidtype polymer (10⁻⁴ S/cm).