Crystallization of Metallocene-Made Isotactic Polypropylene: Disordered Modifications Intermediate between the α and γ Forms

• DOI: 10.1021/ma020648r
• Publication Date: 2002-11-12T18:31:28Z
• Authors: Finizia Auriemma; Claudio De Rosa
• Keywords: DEFECTS; Polymorphism; ISOTACTIC POLYPROPYLENE; ISOTACTIC POLYPROPYLENE; DEFECTS; Polymorphism; 01 natural sciences; 0104 chemical sciences

A detailed analysis of the structure and the thermal behavior of samples of isotactic polypropylene (iPP) prepared with a highly regiospecific metallocene catalysts is presented. The samples present variable amounts of stereodefects (isolated rr triads) and provide the first example of metallocene-made iPP not including regioirregularities. They crystallize from the melt in mixtures of the α and γ forms. The content of the γ form increases with increasing the crystallization temperature, reaches a maximum value, and then decreases for a further increase of the temperature. The crystallization of the γ form is favored by the presence of stereodefects. The thermal analysis has indicated that the crystals of γ form melt at lower temperature than the crystals of α form obtained at the same crystallization temperature. A comparison between the experimental X-ray diffraction profiles of the melt-crystallized samples and the calculated profiles for models of structure has shown that the γ form obtained in these ...