Study On The Terahertz Spectroscopy Of Crystalline Polymeric Systems Containing Hydrogen Bonds

THz spectroscopy technology has attracted wide attention recently.Due to the fact that it can respond to reveal essential information of the lattice vibration,lateral vibration and hydrogen bond vibration of macromolecules,THz technology,thus,provides a new method for studying the complex polymeric systems.Polymorphism phenomenon and hydrogen bonding effects are prevalent in the polymers and polymer composites.Therefore,in this dissertation THz spectroscopy was employed as the main mean to study the crystal structure and hydrogen bonding interaction in crystalline polymers and polymeric systems.The research contents and achievements are mainly concules as:Firstly,the THz absorption spectra of PLA with different crystal forms had been studied.It was found that the closer packing behavior of PLA molecular chains in crystal lattices the stronger THz characteristic absorption peak.The characteristic absorption peaks of ?' crystal,? crystal and stereocomplex crystal of PLA are located at 1.82,2.01 and 2.09 THz,respectively.The obvious different absorption peaks between PLA ?-form and ?'-form crystals provides a more effective method to study the ?'?? crystal transformation mechanism.More important,PLA stereocomplex crystal shows a distinguishing and extremely stronger absorption peak at 1.43 THz when compared with homo-PLA crystals.This 1.43 THz peak was proved to be stemmed from the collective vibration of L-lactic unit and D-lactic unit pairs connecting by hydrogen bonds,and it is the first time that THz spectroscopy has been proved to be powerful in identification of polymer stereocomplex.Secondly,the temperature-dependent crystallization behavior of PHB and orther polymers were studied by THz spectroscopy,and we got conclusions as follows: The THz absorption peak associated with hydrogen bond vibration in PHB molecules shifts from 2.43 to 2.52 THz with the increase of crystallization temperature,which is due to the fact that the more perfect hydrogen bond interaction forms in PHB.When no hydrogen bond or only weak hydrogen bond interaction forms in crystal structure,no THz absorption peak connecting to hydrogen bonding interaction could be observed.Finally,the responses of THz spectroscopy on different crystal forms of PEO/urea complexes and the ??? crystal transition process were investigated.And some conclusions were obtained as follows: The characteristic THz absorption peaks of ?-form PEO/urea complex are 1.12 and 1.24 THz,which had been proved to be stemmed from the hydrogen bond vibrations between urea and urea and the hydrogen bond vibration between PEO and urea,respectively.The characteristic THz absorption peak of ?-form PEO/urea complex is 1.48 THz,which is due to the hydrogen bond vibration mode between urea and urea.The polarization THz spectrum indicates that the hydrogen bond between urea and urea is rotated by 90° during the ??? transition of PEO/urea complex.The response of polymers and polymeric systems in THz frequency region generally occurs within the range of 1~3 THz.Therefore,THz spectroscopy can serves as an effective method for studying the crystal structure and crystal transformation mechanism of polymer systems.