Dielectric relaxation in solutions of poly(p-methoxy phenyl acetylene) and poly(p-chloro phenyl acetylene)

Abstract

The dielectric properties of solutions in toluene of poly (p-methoxy phenyl acetylene) and poly(p-chloro phenyl acetylene) have been compared with those of solutions of poly(p-methoxy styrene) and poly(p-chloro styrene) over the frequency range 10² to 3 × 10⁹Hz. The linear polyenes exhibit two relaxation regions. The low-frequency process is ascribed to the existence of backbone dipoles arranged unidirectionally along the chain. The high-frequency process is ascribed to the simplest mode of motion of the side group dipole. For the p-methoxy compounds this is rotation of the methoxy group. For the p-chloro compounds it is suggested that the motion involves simultaneous rotation of backbone single bonds and the substituent phenyl group. These results are in accord with a model of the polyene in which bond alternation is pronounced, and rotation around the formal single bonds in the chain is facile.