Characterizing polymorphism and crystal transformation of polylactide by terahertz time-domain spectroscopy

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• 作者：Han Li^a ; Hai-Mu Ye^a ; ^{yehaimu@cup.edu.cn} ; Yuping Yang^b ; ^{ypyang_cun@126.com}
• 关键词：Terahertz time-domain spectroscopy ; Polylactide ; Crystal transformation ; Stereocomplex
• 刊名：Polymer Testing
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：57
• 期：Complete
• 页码：52-57
• 全文大小：1570 K
• 卷排序：57

文摘

Terahertz time-domain spectroscopy (THz-TDS), which has been proved to show promising application in complex polymer systems, was employed to investigate the polymorphism phenomenon and crystal transformation of polylactide (PLA) in this study. The THz-TDS shows sensitive response on the crystal structure. The α'-form, α-form and stereocomplex crystals exhibit absorption peaks of lattice vibration at 1.82, 2.01 and 2.09 THz, respectively. THz-TDS has no direct chirality identification on the difference between poly (d-lactide) (PDLA) and poly(l-lactide) (PLLA). However, the PLA stereocomplex shows an extra and distinctive absorption peak at 1.43 THz compared with homo-PLA, and the peak was proved to be stemmed from the collective vibration of L-lactic unit and D-lactic unit pairs connecting by hydrogen bonds. This is the first time that THz-TDS has been proved to be of great potential in identification of polymer stereocomplex crystal. Also, the α'→α crystal transformation of PLA were intuitively investigated at 120 °C using THz-TDS, while the transformation rate was quite slow.