3C08
テラヘルツ周波数領域における高分子の振動分光（理研 1, 関西学院大 2, 近畿大 3, 宮城教育大 4） 保科宏道 1, 山本茂樹 2, 森澤勇介 3,石井伸弥 1,4, 鈴木晴 1, 佐藤春実 2, 尾崎幸洋 2, 内山哲治 4, 大谷知行 1

Vibrational spectroscopy of polymer in terahertz frequency region(RIKEN1, Kwansei Gakuin University2, Kinki University3, Miyagi University ofEducation4) Hiromichi Hoshina1, Shigeki Yamamoto2, Yusuke Morisawa3, ShinyaIshii1,4, Hal Suzuki1, Harumi Sato2, Yukihiro Ozaki2, Tetsuji Uchiyama4, Chiko Otani1

Introduction
Absorption spectra of organic molecules in THz frequency region (0.1-10 THz) show
vibrational peaks which reflect their molecular structure.

In particular, intermolecularinteractions such as the hydrogen bond are key to understanding THz spectra,
because THz spectral features dramatically change with the intermolecularconformations. THz spectroscopy may become a powerful tool to investigate
polymers because their physical properties highly depend on their intermolecularconformation.
In this paper, THz absorption spectra of polymers containing hydrogen bonds werestudied. The hydrogen bond is one of the tightest intermolecular interactions whichmake firm crystal structures in polymers. The spectra show absorption peaks due tothe vibration of the hydrogen bonds.
Experiments
THz absorption spectra of two kinds of polymers, PHB and Nylon, were measured.
The samples were first melted and then slowly cooled down to room temperature toform a film shape. A THz time-domain spectrometer (AISPEC pulse IRS 2300) and aFourier transform far infrared spectrometer (ABB Bomem Inc.: DA8, JASCO FARIS)
were used for the measurement. For the polarization spectroscopy, the samples
were heated to 165 C and stretched to align the direction of the crystal axis.
Temperature dependent spectra were measured by controlling the sample
temperature with a liquid-helium-cooled cryostat and a heating stage.
Results and Discussions
Figure 1 shows the absorption spectra of PHB measured at at 10 K, 300 K, and 440
K. The peak positions shift with the temperature due to the anharmonicity of thevibrational potential (shown by the dashed lines). The polarization dependence of

the peaks is shown on the top of each peak,and was obtained by changing the angle
between the THz electric field and the caxis of the crystal.
Polarization
dependence helps us to understand thedirection of vibrational dipole moments.
We have also measured low-frequency
Raman scattering in this frequency region.
THz and Raman spectra were comparedwith the DFT calculations with Cartesian
coordinate tensor transfer method, andvibrational modes of the peaks areassigned. For example, the peak at 2.82
THz has a vibrational dipole moment
perpendicular to the c axis, and is observedin both THz and Raman spectra. Thismode was assigned as the combination
band of C=O and CH3 bending motion,
which changes the distance of C=OH-Chydrogen bond.
We applied those assignments for thestudy of polymer-crystallization process.

Fig. 1: THz absorption spectra of PHB
measured

at10 K,

300 K

and440 K.

Polarization and assignments are shown.

PHB was isothermally crystallized at 90 C and spectral change was observed as afunction of time. By using two-dimensional correlation spectroscopy, spectra clearlyshow the sequential change of the peak intensities, which clearly suggests thatvibration of hydrogen bond grows faster than the other modes during crystallization.
Conclusion
THz spectra of PHB were measured and successfully assigned. The results of theassignment provide information about higher order conformation and the role ofhydrogen bonds in the crystallization of PHB. We also measured Nylon polymers
that have N-HO=C hydrogen bonds.

Detail of those results will be discussed.

Reference[1] H. Hoshina et al, Appl. Phys. Lett, 96, 101904, 2010[2] H. Hoshina et al, Phys. Chem. Chem. Phys, 13, 9173-9179, 2011[3] H. Hoshina et al, Appl. Phys. Lett, 100, 011907, 2012