Synthesis and properties of polyacetylenes having substituted azobenzene pendant groups

Azobenzene-containing polyacetylenes, poly[(4-butoxyphenyl)(4-ethynylphenyl)diazene] [poly(BuOEAB)] and poly[4-(4-ethynylphenylazo)benzoic acid hexyl ester] [poly(HexOCOEAB)] with number-average molecular weights ranging from 2,800 to 104,000 were synthesized by the polymerization of the corresponding acetylene monomers by [RhCl(norbornadiene)](2) catalyst in conjunction with Et3N, Ph2C=C(Ph)Li, and PPh3 as cocatalysts in toluene and THF in good yields. The polymers exhibited thermogravimetric curves with inflection points corresponding to cleavage of butyl ether and hexyl ester groups. The trans-azobenzene moiety of poly(BuOEAB) isomerized into cis-form upon UV-irradiation at the wavelength of 300-400 nm both in solution and in the filmy state. Oil the other hand, poly(HexOCOEAB) did not isomerize under the same condition.