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.
Emerging technological applications for complex polymers require insight into the dynamics of these materials from a molecular and nanostructural viewpoint. To characterize the orientational response at these length scales, we developed a versatile rheooptical Fourier transform infrared (FTIR) spectrometer by combining rheometry, polarimetry, and FTIR spectroscopy. This instrument is capable of measuring linear infrared dichroism spectra during both small-strain dynamic deformation and large-strain irreversible deformation over a wide temperature range. The deformation response of quenched and slow-cooled isotactic polypropylene (iPP) is investigated. In quenched iPP, under dynamic oscillatory strain at an amplitude of ϳ0.1%, the dichroism from the orientation of the amorphous chains is appreciably less than that from the crystalline region. At large irreversible strains, we measured the dichroic response for 12 different peaks simultaneously and quantitatively. The dichroism from the crystalline peaks is strong as compared to amorphous peaks. In the quenched sample, the dichroism from the crystalline region saturates at 50% strain, followed by a significant increase in the amorphous region dichroism. This is consistent with the notion that the crystalline regions respond strongly before the yield point, whereas the majority of postyielding orientation occurs in the amorphous region. Our results also suggest that the 841 cm Ϫ1 peak may be especially sensitive to the 'smectic' region orientation in the quenched sample. The response of the slow-cooled sample at 70°C is qualitatively similar but characterized by a stronger crystalline region dichroism and a weaker amorphous region dichroism, consistent with the higher crystallinity of this sample, and faster chain relaxation at 70°C.
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