The microstructure of chains of isotactic polypropylene (iPP) strongly influences its crystallization behavior. Single-center metallocene catalysts allow a perfect control over the microstructure, and iPP samples characterized by different kinds and amounts of regio- and stereo-irregularities and different molecular weights, can be produced. Tailoring the chain microstructure affords opportunities for a fine tuning of the physical properties and iPP samples having different melting temperatures and properties of stiff thermoplastic materials or of elastomers, can be obtained. It has been reported that the crystallization of α and γ form of iPP is related to the presence of stereodefects, regiodefects and constitutional defects. Since in metallocene-made iPPs the defects are randomly distributed along the polymer chains even a small amount of defects shortens the length of the regular isotactic sequences, reducing the melting temperature and favoring the crystallization of the γ form.
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