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

Abstract

AbstractA 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 (M̄n = 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 (M̄n = 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 (M̄n = 80,800) was 635 nm and shifted to 880 nm by heat treatment of the polymer. © 1995 John Wiley & Sons, Inc.