Negative excess volume of mixing in polybutadiene/polyisoprene blends

Abstract

AbstractThe temperature dependence of specific volume was measured for miscible polybutadiene/polyisoprene blends by dilatometry. The negative excess volume of mixing below the lower critical solution temperature was studied in terms of the Flory equation‐of‐state. In order to achieve a best‐fit of the calculated excess volume to the experimental excess volume, Flory's interaction parameter X12 was estimated to be negative for the blend. Thus, a stereo structural effect for mixing would be predicted, since only van der Waals dispersion forces are expected between blend components. Considering that one way to observe the stereo‐structural effect is to study conformational changes during mixing, solid‐state proton NMR measurements were conducted. Evidence of a conformational change was obtained for the blend. The occurrence of a structural effect was also suggested. © 1994 John Wiley & Sons, Inc.