Deformation-Induced Morphology Changes and Orientation Behavior in Syndiotactic Polypropylene

Abstract

Syndiotactic polypropylene (sPP) exhibits a complex crystalline morphology, characterized by unique annealing- and deformation-induced changes. Rheooptical FTIR spectroscopy, wide-angle X-ray diffraction (WAXD), and Raman spectroscopy are used to characterize morphology and orientation responses of highly syndiotactic sPP to tensile drawing. Solid-state thin films of different initial morphology, either quenched or slowly cooled from the melt, are studied. Results suggest that a gradual transition in macromolecular chain conformation, from gauche−gauche−trans−trans helical to all-trans planar, is observed at room temperature for quenched samples that are drawn up to 400% strain. This transition is marked initially by the gradual disappearance of helical chains (disordered form I) and the subsequent emergence of a mesophase, which may transform into form III crystals at even greater strains. Our primary investigational tool, the rheo-FTIR spectrometer, allows us to monitor the presence and orientation of amorphous, mesomorphic, and crystalline domains directly, simultaneously, and sensitively. Results from all of the techniques used are correlated in an effort both to assign IR peaks to characteristic sPP moieties and to generate a plausible physical model of the deformation dynamics in melt-quenched sPP.

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