AbstractDensity gradient sedimentation of polystyrenes, Hevea rubber and syntheticcis‐1,4‐polyisoprene was studied in the systems ethylene bromide‐mesitylene and (1,2‐dibromo‐1,1‐difluoroethane)‐cyclohexene. The latter system has very closely matched refractive indices at atmospheric pressure. This work was oriented toward the analysis of mixed polymer and copolymers. Large density gradients were used with schlieren optics. No difference between the points of accumulation of polystyrene from different types of polymerization nor between Hevea andcis‐polyisoprene could be found under the conditions employed. Narrow gradient patterns could be produced for polymers ofMv= 200,000. These broadened with increasing polymer concentration. AtM= 106it is believed to be possible to estimate semiquantitatively concentrations of polystyrene of 5 ppm. A method of estimating the amount of a component present in terms of its gradient pattern is given. The density distribution in the bromofluoroethane system was studied by the use of inert marker substances o
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