DYNAMICS OF POLYBUTADIENES WITH DIFFERENT MICROSTRUCTURES .2. DIELECTRIC RESPONSE AND COMPARISONS WITH RHEOLOGICAL BEHAVIOR

A series of 1,2-1,4-polybutadienes with varying 1,2 (vinyl) content wa s investigated using time-domain dielectric spectroscopy, The time ran ge was 10(-5)-300 s, which can be converted by Laplace transform to a frequency range of 10(-3)-6000 Hz. The samples were the same as those used in a previous rheological study from these laboratories. Therefor e, a direct comparison of dielectric and mechanical responses was poss ible. Within experimental uncertainty, the ct relaxation observed by b oth methods shows the same temperature dependence but there is an offs et between the characteristic times of both methods, which increases w ith increasing vinyl content. This result can be qualitatively underst ood from the difference of the size of the dipolar groups, viz, cis an d vinyl monomeric units, in the context of the DiMarzio-Bishop model. In addition, the question of time-temperature superposition was studie d using the dielectric data. In the cases of a vinyl content equal to or greater than 0.53 no deviations from time-temperature superposition -were detected. Only for the sample with the lowest vinyl content (0.0 7) does the attempt to construct a master curve from the dielectric lo ss data fail. In this case a fit with a combination of a Havriliak-Neg ami and a Cole-Cole functions suggests that this deviation from time-t emperature superposition is an intrinsic feature of the ct alpha relax ation rather than an effect of its merging with the beta relaxation, T he absence of indications for such, a deviation in the rheological stu dy can be explained by the smaller frequency range of the latter. This stresses the necessity of a large dynamic range in experiments aimed at the examination of the time-temperature superposition principle. (C ) 1997 American Institute of Physics.