| Abstract
| - The polymorphic behavior of samples of isotactic polypropylene prepared with unbridgedoscillating metallocene catalysts is analyzed and compared with the behavior of samples prepared witha chiral isospecific metallocene catalyst having similar amounts of defects of stereoregularity. In thesamples prepared with the unbridged catalysts, the amount of γ form, which develops upon melt-crystallization procedures, turns out to be always lower than that in the samples prepared with the chiralisospecific catalyst. This suggests that, in the samples obtained with the unbridged catalysts, thedistribution of defects of stereoregularity is not random, the defects being segregated in morestereoirregular regions of the chains, and confirms that these samples are characterized by a stereoblockstructure, with long isotactic sequences alternating to atactic or more stereoirregular sequences. Anempirical method to establish the degree of segregation of defects along polypropylene chains is suggested.
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