Synthesis of π-conjugated polymers possessing 1,3-butadiene-1,4-diyl units by reactions of regioregular organometallic polymer having titanacyclopentadiene moieties in the main chain [1]

The synthesis and properties of π-conjugated polymers possessing phenylene-1,4-diyl and 1,3-butadiene-1,4-diyl alternating units in the main chain by reactions of a regioregular organometallic polymer having titanacyclopentadiene-2,5-diyl unit are described. The polymerization of 1,4-diethynyl-2,5-dioctyloxybenzene with a low-valent titanium complex, generated in situ from titanium(IV) isopropoxide and isopropyl magnesium chloride, was carried out at −78 °C to −50 °C for 12 h to give the regioregular organotitanium polymer. The diene-containing π-conjugated polymers were obtained by the reactions of the organotitanium polymer with electrophiles such as hydrochloric acid and iodine. For example, the reaction with hydrochloric acid gave a diene-containing polymer in a 61% yield whose Mn and Mw/Mn were estimated as 5700 and 1.61, respectively (by GPC). The π-conjugated character of the resulting polymer could be supported by its UV–vis spectrum. That is, the absorption maximum (λmax) of the polymer was observable at 470 nm, which was bathochromically shifted by 115 nm compared to that of a model compound (1,4-bis(2-methoxyphenyl)-1,3-butadiene, λmax = 355 nm).