Abstract
The crystallization of cured natural rubber and synthetic cis-1,4-polyisoprene was investigated by directly following the volume change on stretching and releasing. For this purpose, a dilatometer was constructed, which contained a stretching device in the sealed apparatus. The specimen was stretched and released in a step wise manner at a constant temperature and the volume change was read out. At higher elongations the volume of the specimen showed a large decrease by increasing the extension ratio, and this was confirmed to be due to crystallization by X-ray measurements. When the crystallization occurred, the volume decreased slowly after stretching and reached a constant value within an hour. Such a time dependence of the volume change was not found in the releasing process. The relationship between the extension ratio and the volume change gave straight lines inflected at the extension ratio αc on the stretching steps, and αm on the releasing steps, and αc was always higher than αm. The value αc indicated the extension ratio at which crystallization begins on stretching, while the value αm indicated the extension ratio at which the last traces of crystallinity disappear on releasing. These two values of synthetic cis-1,4-polyisoprene are higher than those of natural rubber. The rate of crystallization of synthetic cis-1,4-polyisoprene on stretching is essentially the same as that of natural rubber.
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Tanaka, Y., Tadokoro, H. Characterization of Diene Polymers.1 II. Dilatometric Measurements of Crystallization on Stretching. Polym J 1, 656–659 (1970). https://doi.org/10.1295/polymj.1.656
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DOI: https://doi.org/10.1295/polymj.1.656
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