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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 II: Study of Poly(-Caprolactone) Homopolymer and a Poly(3-Hydroxybutyrate)Poly(-Caprolactone) Blend
Volume 63, Number 9 (Sept. 2009) Page 1034-1040
Unger, Miriam; Morita, Shigeaki; Sato, Harumi; Ozaki, Yukihiro; Siesler, Heinz W.
In the present study, variable-temperature Fourier transform infrared (FT-IR) spectra of a poly(ε-caprolactone) (PCL) homopolymer and a poly(3-hydroxybutyrate) (PHB)-poly(ε-caprolactone) (PCL) blend were analyzed by generalized two-dimensional correlation spectroscopy (2DCOS) and perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy. The C=O stretching vibration bands of PCL and PHB were employed to explore the structural changes in the PCL homopolymer and the PHB-PCL blend during the heating process. For the melting of PCL homopolymer in the temperature range of 50 to 70 °C, we observed in the synchronous and asynchronous 2D correlation spectra one crystalline (1724 cm−1) and one amorphous (1737 cm−1) C=O stretching vibration band, which are also detectable in the one-dimensional FT-IR spectra. This result was also confirmed by PCMW2D correlation spectroscopy. During the heating process of the PHB-PCL blend in the temperature range 30-200 °C, the PCMW2D correlation analysis provided detailed information. Thus, in the synchronous PCMW2D correlation spectrum the melting of PCL was observed in the temperature region between 30 and 70 °C. The recrystallization of PHB in the blend in the temperature range 70-120 °C was accompanied by a shift of the C=O stretching band from higher wavenumber (1724 cm−1) corresponding to an imperfect crystalline state to the lower wavenumber (1721 cm−1) characteristic of a well-ordered crystalline state. In the temperature range 120-200 °C the melting process of PHB in the blend is captured by a sharp transition from the crystalline (1722 cm−1) to the amorphous (1747 cm−1) C=O stretching band.