Dielectric Normal Mode Process in Semidilute and Concentrated Solutions of Poly(2,6-dichloro-1,4-phenylene oxide)

Abstract

The dielectric normal mode process was investigated on semi-dilute and concentrated solutions of poly(2,6-dichloro-1,4-phenylene oxide)(PDCPO-M) in a good solvent, chlorobenzene, at 300 K. Four linear, short chain samples with molecular weight M less than 20×103, two nearly linear samples of intermediate M, and a high M, randomly branched sample (PDCPO-380) of M=380×103 were used. The dielectric relaxation time τ for 40 wt% solutions of the linear samples was approximately proportional to M2, indicating Rouse behavior of non-entangled chains. The loss curves of the PDCPO-17 solutions were symmetrical in shape, and the half width A increased slightly with increasing concentration C due presumably to the increase in the local friction constant ζ. On the other hand, for the branched, high M PDCPO-380 sample, its loss curve not only became broader with increasing C, but split into two peaks at about C=30 wt%. This is presumably because the relaxation time of longer branches of the sample were retarded more strongly by entanglement. From the relaxation strength, the mean square end-to-end distance ‹r2› was determined as a function of C for PDCPO-17 solutions. The slope of the log‹r2› vs. logC plot was approximately −0.08 in the range of 0.2<C<1.0. This value is much smaller than −0.25 expected from the scaling theory. This discrepancy may be attributed to the weak excluded volume effect for the low molecular weight sample.