Effect of Substrates on the Addition Polymerization of 1,4-Benzenedithiol to 1,4-Diethynylbenzene in the Solid State and the Electronic Properties of the Resulting Polymer

The effect of substrates on the addition polymerization of 1,4-benzenedithiol (BDT) to 1,4-diethynylbenzene (DEB) in the solid state and the electronic properties of the polymers obtained were studied. As the substrate polymer sheets, for instance, PET (poly (ethylene terephthalate)) sheet, ON-6 (oriented nylon-6) sheet and so on having surface free energies Γ_s from 27.4 to 55.0 erg/cm² were used. At the monomer sublimation temperature of 60°C, the S wt% (sulfur content) and the cis content of the polymers were not affected by the kind of polymer sheets. However, the molecular weights, M¯_n of the polymers polymerized on the polymer sheets were 13,000–30,000, and the values were several times higher than the molecular weight of the polymers polymerized on glass plate. On the other hand, at the sublimation temperature of 82°C, the cis content of the polymers apparently increased with decreasing d-value of the polymer sheets. On X-ray diffraction patterns of monomer mixtures sublimed onto polymer sheets, the diffraction intensities and the diffraction peak positions were concerned with the d-value of the polymer sheets. Using polymer sheets, the diffraction peak intensities of the monomer mixture at 7.73 and 7.58 Å decreased compared with those on glass plate. In contrast, the peak at 3.65 Å, which is a negligibly small peak on glass plate, obviously increased. However, as the d-value of the polymer sheets (PET 3.45 Å; OPP (oriented polypropylene) 5.2 Å) increased, the diffraction peak intensities at 7.73 Å and 7.58 Å gradually increased and the diffraction peak intensity at 3.65 Å gradually decreased. The parallel electrical conductivities (σ_||) toward the layered structural polymer on PET, ON-6 and glass plate under air atmosphere were 10^?7, 10^?9 and 10^?11 S/cm, respectively. Under a reduced pressure of 10^?3 mmHg, the σ_|| values of each polymer lowered by one or two orders of magnitude. On the other hand, the σ_|| values of the nonlayered structural polymers under air atmosphere were about 10^?11–10^?12 S/cm and were independent of the substrates. Even under a reduced pressure of 10^?3 mmHg, the σ_|| values hardly changed and remained at 10^?11–10^?12 S/cm. The vertical electrical conductivities (σ_?) of the layered structural polymers on conductive PET sheet coated by indium tin oxide or NESA glass plates were independent of the substrates and were 10^?14 S/cm under air atmosphere. The σ_? values of the nonlayered structural polymers also exhibited the same values. The reversible change of the amount of the layered structural polymer on PET sheet was also caused by irradiation of the photo-light which is the effective wavelength for the phase transition of the polymers mounted on glass plate. The σ_|| value of the layered structural polymer on ON-6 sheet reversibly changed with the amount of the layer structure controlled by the photo-light, that is, the σ_|| increased up to about one order of magnitude by the photo-light at 545.6 nm. On the other hand, the _|| decreased to about one order of magnitude by the photo-light at 539.6 nm. Anisotropic conductivity with respect to σ_|| and σ_?, and oxygen doping mechanisms were discussed in relation to the layer structure of polymers. © 1997 John Wiley & Sons, Ltd.