Simultaneous crystallization of isotactic and syndiotactic sequences of polypropylene

Polypropylene samples contg. 45% isotactic and 20% syndiotactic pentads were characterized by calorimetry and solid-state NMR. Iso- and syndio-sequences are able to crystallize in the same sample to form a complex mixt. of several allomorphs: monoclinic a2 phase together with disordered a phases for isotactic and extended chain together with helix forms for syndiotactic stereosequences. The fraction of each phase was established quant., due to the limited overlapping of the signals at room and high temp. The partition of stereosequences between the amorphous and cryst. phases was detd. at room and high temp. The distribution of the stereosequences in the amorphous phase was established at high temp. at the pentad level; thus, it was possible to det. the stereosequences already crystd. at that temp. Hydrogen spin-lattice relaxation times in the rotating frame, measured under spin diffusion conditions, demonstrate the segregation of iso- and syndiotactic crystallites and the intimacy of the phases of the same tacticity.