Abstract
The microstructure and morphology of stereoblock polypropylenes containing sequences of isotactic (i) and syndiotactic (s) polypropylene (PP) were studied by 13C NMR spectroscopy, wide angle x-ray scattering (WAXS), size exclusion chromatography (SEC) combined with FT-IR analysis of the fractions, and atomic force microscopy. The 13C NMR spectra show the presence of long stereoregular sequences in the respective stereoblock polypropylene which are able to form the crystal modification known from the respective stereoregular homopolymers as revealed by WAXS measurements. A bimodal molar-mass distribution is detected by SEC. All SEC fractions contain i-PP and s-PP sequences, proven by FT-IR spectroscopy. It is shown by atomic-force microscopy that the stereoblock polypropylene, synthesized by homopolymerization of propylene using iso- and syndiotactic catalysts, form a microphase-separated morphology. The microphase separation is preserved also after treatment with hot toluene. A parallel investigation was conducted on a blend of i-PP and s-PP; it exhibits macrophase separation. Treatment of the blend with hot toluene results in the dissolution of the s-PP phase.
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