Synthesis and Electric Conduction of Acceptor-Type Poly(diacetylene)

Abstract

1, 6-Dibromo-2, 4-hexadiyne has been polymerized in a vacuum by heating, resulting in the formation of a conjugated polymer. The polymer is soluble in dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF), and can be formed into thin films. Its molecular weight is estimated at 25000 by gel permeation chromatography (GPC). The polymer is an acceptor and makes change-transfer (C-T) complexes with donors such as ammonia and tetrathiafulvalene (TTF). Consequently, its conductivity increases to 10^-1S·cm^-1, as shown in Table 1 and 2. Acceptor molecules such as iodine and tetracyanoquinodimethan (TCNQ), however, don't cause the conductivity to increase very much (up to 10^-6-10^-7S·cm^-1). That is quite different from the property of the usual conducting polymers such as polyacetylene. The single crystal of poly(2, 4-hexadiyne-1, 6-diyl ditosylate) and the pellet of the cross-linked polyester made from 2, 4-hexadiyne-1, 6-diol and adipoyl dichloride also form the C-T complexes with ammonia, their conductivities being raised up to 10^-4-10^-6S·cm^-1, as shown in Fig.5. The electron-withdrawing abilities of these poly(diacetylene)s depend on their resonance structure shown in Equation (2): the positive charge exists on their polymer backbones, and the negative one on their substituents. The strength of poly(diacetylene) as acceptor or as donor can be controlled by changing its substituent. The acceptor-donor relations among poly(diacetylene)s and dopants are proposed in Fig.6.