The flow birefringence of an isotactic sample of polystyrene is investigated in bromoform at room temperature, and in o-dichlorobenzene in a broad range of temperatures. In the latter solvent the stress optical coefficient appears to be nearly independent of temperature. In this way no evidence could be found for a conformational transformation, which has been proposed to occur at 80°C. The presence of relatively large particles (crystal nuclei) becomes apparent from an anomaly of the extinction angle curve when measured on o-dichloro-benzene below 80°
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