Yao Shu-Fang, Chen Xiao-Tong, Ye Hai-Mu
Department of Materials Science and Engineering, China University of Petroleum , 102249 Beijing, P. R. China.
J Phys Chem B. 2017 Oct 12;121(40):9476-9485. doi: 10.1021/acs.jpcb.7b07954. Epub 2017 Sep 29.
The detailed structure and crystallization behavior of poly(butylene succinate) (PBS) have been investigated by Fourier transform infrared (FTIR) and other methods systematically. For the first time, we confirmed that the C═O stretching modes of PBS can respond to three distinguish absorption bands in the FTIR spectrum, at around 1736, 1720, and 1714 cm respectively. The 1736 cm band is adopted as the stretching mode of C═O groups in free amorphous fraction (MAF); the 1714 cm band which is relevant to more stable structure, displays more anisotropic in polarized FTIR spectra, and has been confirmed as stretching vibrations of hydrogen-bonded C═O groups in the crystalline phase. The 1720 cm band is linked to crystallization but comes from less ordered structure. Moreover, the 1720 cm band can be destroyed prior to 1714 cm band during heating and constructed behind 1714 cm band during cooling. Thus, the 1720 cm band is reasonably ascribed to the C═O groups in rigid amorphous fraction (RAF) or intermediate phase which locates between MAF and crystalline phase. The corresponding investigation by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) further supports that the three particular C═O absorption bands indeed reveal the typical three-phase structure for PBS. More important, the FTIR spectrum of PBS is very sensitive to sample preparation process and measurement mode. The relative content of each band depends on the crystallization temperature (T) and measured thickness. The higher T, the more RAF content appears when measured at room temperature; the thinner penetration thickness of FTIR measurement, the less RAF content can be detected, and the penetration thickness-dependent behavior is suggested as the result of higher mobility of chains in the air/bulk surface. Additionally, the particular three absorption bands of C═O groups in PBS force us to carefully reconsider previous reports on structure and interaction state obtained by FTIR spectroscopy in PBS and its composites.
通过傅里叶变换红外光谱（FTIR）等方法系统地研究了聚丁二酸丁二醇酯（PBS）的详细结构和结晶行为。首次证实，PBS的C═O伸缩振动模式在FTIR光谱中可对应三个不同的吸收带，分别位于约1736、1720和1714 cm⁻¹处。1736 cm⁻¹处的吸收带被用作自由非晶部分（MAF）中C═O基团的伸缩振动模式；与更稳定结构相关的1714 cm⁻¹处的吸收带在偏振FTIR光谱中表现出更强的各向异性，并已被确认为结晶相中氢键合C═O基团的伸缩振动。1720 cm⁻¹处的吸收带与结晶有关，但来自有序程度较低的结构。此外，在加热过程中，1720 cm⁻¹处的吸收带会先于1714 cm⁻¹处的吸收带被破坏，而在冷却过程中则会在1714 cm⁻¹处的吸收带之后形成。因此，1720 cm⁻¹处的吸收带合理地归因于刚性非晶部分（RAF）或位于MAF和结晶相之间的中间相中的C═O基团。差示扫描量热法（DSC）和广角X射线衍射（WAXD）的相应研究进一步支持了这三个特定的C═O吸收带确实揭示了PBS的典型三相结构。更重要的是，PBS的FTIR光谱对样品制备过程和测量模式非常敏感。每个吸收带的相对含量取决于结晶温度（T）和测量厚度。T越高，在室温下测量时RAF含量越高；FTIR测量的穿透厚度越薄，检测到的RAF含量越少，而穿透厚度依赖性行为被认为是由于空气/本体表面链的流动性较高所致。此外，PBS中C═O基团的这三个特定吸收带迫使我们重新仔细考虑以前关于通过FTIR光谱法在PBS及其复合材料中获得的结构和相互作用状态的报道。
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