Addition polymerization of 2-cyano-1, 4-benzenedithiol to 1,4-diethynylbenzene and properties of polymers

A novel addition polymerization of 2-cyano-1,4-benzenedithiol to 1,4-diethynylbenzene was carried out by UV irradiation in toluene at 50°C under nitrogen atmosphere. The polymerization proceeded readily, and a pale-yellowish conjugated polymer contain-ing sulfur atoms and cyano groups (M?_n = 20,400–80,800) was obtained in a 60–80% yield for 120–250 min. The polymer was found to be 1 : 1 alternating structure of anti-Markownikoff's type and was insolu-ble in conventional organic solvents. Since the polymer having molecular weight of the order of 10⁴ had a softening point at 115°C, a thin polymer film was obtained by heat press. TG analysis of the polymer indicated its decomposition point at about 620°C under argon atmosphere. The electrical conductivity of the polymer pellet was 10^?10 S/cm at 300 K without doping and on the order of 10^?5 S/cm on I₂ doping. Fur-thermore, the electrical conductivity of the undoped polymer pellet reversibly changed from the order of 10^?10 S/cm at 300 K to 10^?7 S/cm at 435 K with temperature variation, accompanying with increasing carrier density and mobility. The polymer pellet (M?ⁿ = 80,800) aged at 250°C for 5 min under nitrogen atmosphere exhibited the order of 10^?7 S/cm at 300 K. Thermal treatment of the polymers was thought to cause spreading of conjugated system through molecular rearrangement supported by x-ray diagrams. An absorption edge of diffuse reflectance spectra of the polymer (M?ⁿ = 80,800) was 635 nm and shifted to 880 nm by heat treatment of the polymer. © 1995 John Wiley & Sons, Inc.