Abstract
AbstractTheoretical treatment had shown that syndiotactic propagation should be slightly favored energetically over isotactic propagation in free radical vinyl chloride polymerization. This prediction has been confirmed experimentally by x‐ray and infrared investigations of vinyl chloride polymers prepared at various temperatures. The initiator was a peroxide, azodiisobutyronitrile, or tri‐n‐butylboron, and had no detectable influence on the x‐ray and infrared results. As the polymerization temperature is lowered, the number of lines or arcs in the x‐ray diffraction pattern and their sharpness gradually increase as a result of the increased crystallinity arising from improved regularity. The regular sequences are indicated to have the syndiotactic configuration from the chain repeat distance. The change in the infrared absorbance ratio of two carbon‐chlorine stretching bands with polymerization temperature can be interpreted in agreement with increasing syndiotacticity at decreasing temperature. With the use of simplifying assumptions, the activation energy difference between isotactic and syndiotactic propagation is estimated to be of the order of one‐half kcal/mole. The stereoregulated free radical polymerization of vinyl chloride is thus qualitatively similar to that disclosed for other monomers.
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