Simultaneous crystallization of isotactic and syndiotactic sequences of polypropylene

Polypropylene samples containing 45% isotactic and 20% syndiotactic pentads were characterized by calorimetry and solid-state NMR. Iso- and syndio-seq uences are able to crystallize in the same sample to form a complex mixture of several allomorphs: monoclinic alpha (2) phase together with disordered alpha phases for isotactic and extended chain together with helix forms fo r syndiotactic stereosequences. The fraction of each phase was established quantitatively, due to the limited overlapping of the signals at room and h igh temperature. The partition of stereosequences between the amorphous and crystalline phases was determined at room and high temperature. The distri bution of the stereosequences in the amorphous phase was established at hig h temperature at the pentad level; thus, it was possible to determine the s tereosequences already crystallized at that temperature. Hydrogen spin-latt ice relaxation times in the rotating frame, measured under spin diffusion c onditions, demonstrate the segregation of iso- and syndiotactic crystallite s and the intimacy of the phases of the same tacticity.