Electrical conductivity of polydiacetylene, poly[5,7-dodecadiyn-1,12-diol-bis(n-butoxy carbonylmethyl urethane)] gel: 1. Sol-gel transition and conduction mechanism

Abstract

Electrical conductivity, colour change and sol—gel transition behaviour were studied for a polydiacetylene, poly[5,7-dodecadiyn-1,12-diol-bis(n-butoxy carbonylmethyl urethane)] abbreviated as P(4BCMU), in toluene gels. For P(4BCMU)-28 with weight average molecular weight of 280 000, the sol—gel transition temperature was determined to be around 348 K varying slightly depending on the methods employed for the determination. The alternating current (a.c.) and direct current (d.c.) conductivities of P(4BCMU)-28 gels exhibited a broad maximum at ∼336 K. Upon heating the gels, the colour changed from red to yellow at ∼348 K, while upon cooling a sharp colour change was observed at ∼340 K indicating the supercooling of the sol phase. These characteristic temperatures increased with increasing molecular weight. The a.c. and d.c. conductivities were enhanced approximately 20 times by adding a dopant iodine to the gels. We also observed a weak photoconductivity similar to the bulk P(4BCMU). These results suggest that the conduction mechanism of the gels is due predominantly to electronic origins through the gel networks rather than ionic ones in the toluene medium.