Wavenumber Dependence of FT-IR Image of Molecular Orientation in Banded Spherulites of Poly(3-hydroxybutyrate) and Poly(l-lactic acid)

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• 作者：Yuta Hikima ; Junko Morikawa ; Toshimasa Hashimoto
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：February 26, 2013
• 年：2013
• 卷：46
• 期：4
• 页码：1582-1590
• 全文大小：719K
• 年卷期：v.46,no.4(February 26, 2013)
• ISSN：1520-5835

文摘

The chemical and the molecular chain orientation image of a banded spherulite of crystalline polymers, poly(l-lactic acid) (PLLA) and poly(3-hydroxybutyrate) (PHB), are visualized using FT-IR imaging with a newly proposed multipolarization calculation method. The vector representation of FT-IR image at different absorption spectral peaks visualizes the magnitude and direction of molecular chain orientation directly in comparison with the retardation and the slow-axis azimuthal images obtained by birefringence imaging. We found for the first time that the wavenumber dependence of in-plane orientation function in the band structure of a PHB spherulite, which is known as a double-band structure originated from a biaxial refractive index ellipsoid. The 15 absorption peaks in the IR spectrum of PHB can be classified into three groups by a different appearance of a band structure in view of the magnitude of molecular chain orientation. The azimuthal image of birefringence also shows the double-band structure; however, the FT-IR azimuthal images of orientation axis indicate the completely different distribution in which there is no band structure at any IR absorption peaks. By contrast, a good correspondence between the azimuthal image of the slow axis of birefringence and the orientation axis of FT-IR is observed in the spherulite of PLLA, which has a uniaxial refractive index ellipsoid. The advanced FT-IR imaging method clarifies the wavenumber-dependent two-types single-band structures of PHB, indicating the local molecular chain orientation along the crystallographic axes in a unit cell.