Mechanical and Dielectric Spectroscopy of Aroclor, 1,2-Polybutadiene, and Their Mixtures

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Dynamic mechanical and dielectric spectra were obtained in the glass transition zone for Aroclor 1248 (a polychlorinated biphenyl), for a low molecular weight polybutadiene (88% 1,2-microstructure), and for a 50% mixture. The neat materials exhibit two different and unusual characteristics. For Aroclor, the shape of the relaxation function measured mechanically is quite different from the dielectric result. In accord with the well-established correlation between time and temperature dependences, the relaxation times for the (narrower) dielectric spectrum exhibit a weaker temperature dependence. Dielectric and mechanical relaxation functions measured for the polybutadiene are in close agreement; however, the shape of the spectrum varies with temperature. Thus, neat polybutadiene with high vinyl content is thermorheologically complex at temperatures near T g . The 50% mixture displays the previously observed anomaly of isothermal relaxation proceeding faster than that of the neat components. A comparison of this effect as measured mechanically and dielectrically implies that its origin is a positive excess mixing volume