Unger Miriam, Morita Shigeaki, Sato Harumi, Ozaki Yukihiro, Siesler Heinz W
Department of Physical Chemistry, University of Duisburg-Essen, Schuetzenbahn 70, 45117 Essen, Germany.
Appl Spectrosc. 2009 Sep;63(9):1027-33. doi: 10.1366/000370209789379213.
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 degrees C). Non-annealed PHB showed a recrystallization process in the temperature range 30-120 degrees 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 degrees C, it is helpful to use the PCMW2D correlation analysis, which indicates the recrystallization between 40 and 110 degrees 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 degrees 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.
采用广义二维相关光谱法（2DCOS）和扰动相关移动窗口二维（PCMW2D）相关光谱法，通过变温傅里叶变换红外（FT-IR）光谱研究了未退火和退火的聚（3-羟基丁酸酯）（PHB）均聚物的熔融行为。利用C=O伸缩振动的吸收带研究了加热过程（30-200℃）中的结构变化。未退火的PHB在30-120℃温度范围内呈现重结晶过程。在异步二维相关光谱中，我们清楚地捕捉到了C=O伸缩模式的结晶度敏感翼中存在两个组分：较低波数（1718 cm⁻¹）处的有序结晶态和较高波数（1724 cm⁻¹）处的无序结晶态。这些在1718和1724 cm⁻¹处的结晶度敏感带在一维（1D）FT-IR光谱中不易检测到，它们与约1737和1747 cm⁻¹处归因于非晶组分的C=O伸缩吸收带共享异步交叉峰。对于未退火的PHB在120-200℃温度范围内的熔融过程，使用PCMW2D相关分析很有帮助，该分析通过C=O伸缩带从1726 cm⁻¹移至1722 cm⁻¹以及在PHB熔点约190℃时急剧转变为1747 cm⁻¹处的宽非晶C=O伸缩吸收，表明在40至110℃之间发生了重结晶。对于退火的PHB样品，在PCMW2D相关分析中仅观察到从结晶态到非晶态C=O伸缩带的急剧转变的熔融行为。
