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Variable-Temperature Fourier Transform Infrared Spectroscopic Investigations of Poly(3-Hydroxyalkanoates) and Perturbation-Correlation Moving-Window Two-Dimensional Correlation Analysis. Part I: Study of Non-Annealed and Annealed Poly(3-Hydroxybutyrate) Homopolymer

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Abstract:

Generalized two-dimensional correlation spectroscopy (2DCOS) and perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy were applied to explore the melting behavior of non-annealed and annealed poly(3-hydroxybutyrate) (PHB) homopolymer as studied by variable-temperature Fourier transform infrared (FT-IR) spectroscopy. The absorption band of the C=O stretching vibration was employed to investigate the structural changes during the heating process (30–200 °C). Non-annealed PHB showed a recrystallization process in the temperature range 30–120 °C. In the asynchronous 2D correlation spectrum we clearly captured the existence of two components in the crystallinity-sensitive wing of the C=O stretching mode: a well-ordered crystalline state at lower wavenumbers (1718 cm−1) and a less ordered crystalline state at higher wavenumbers (1724 cm−1). These crystallinity-sensitive bands at 1718 and 1724 cm−1, which are not readily detectable in the one-dimensional (1D) FT-IR spectra, share asynchronous cross-peaks with bands at around 1737 and 1747 cm−1 assignable to the C=O stretching absorptions due to the amorphous components. In the case of the melting process of non-annealed PHB in the temperature range 120–200 °C, it is helpful to use the PCMW2D correlation analysis, which indicates the recrystallization between 40 and 110 °C by the shift of the C=O stretching band from 1726 cm−1 to 1722 cm−1 and the sharp change to the broad amorphous C=O stretching absorption at 1747 cm−1 at the melting temperature of PHB around 190 °C. For an annealed sample of PHB only the melting behavior was observed in the PCMW2D correlation analysis by the sharp transition from the crystalline to the amorphous C=O stretching band.

Keywords: 2DCOS; FOURIER TRANSFORM INFRARED SPECTROSCOPY; FT-IR SPECTROSCOPY; GENERALIZED 2D CORRELATION SPECTROSCOPY; MELTING BEHAVIOR; PCMW2DCOS; PERTURBATION-CORRELATION MOVING-WINDOW 2D CORRELATION SPECTROSCOPY; POLY(3-HYDROXYBUTYRATE) (PHB)

Document Type: Research Article

DOI: http://dx.doi.org/10.1366/000370209789379213

Affiliations: 1: Department of Physical Chemistry, University of Duisburg-Essen, Schuetzenbahn 70, 45117 Essen, Germany 2: Division of Energy Science, EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan 3: School of Science and Technology and Research Center for Environment Friendly Polymers, Kwansei Gakuin University, Sanda 669-1337, Japan

Publication date: September 1, 2009

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