聚偏氟乙烯全反式分子链振动模式的研究

利用ab initio分子轨道计算,对β相聚偏氟乙烯(PVDF)的全反式分子链进行了结构优化,计算值和实验值基本符合,且发现C－C－C键角有两种不同的值,112.8°和113.3°.对该分子的频率进行了计算,得到了红外强度谱.在400～4 000 cm-1范围内,对30 μm厚的聚偏氟乙烯取向膜和取向极化膜进行了红外光谱的测量，红外吸收光谱和红外强度谱基本一致.把所有振动模式分成六个系列:系列Ⅰ（544～415 cm-1）,系列Ⅱ（913～792 cm-1）,系列Ⅲ（1 353～998 cm-1）,系列Ⅳ（1 458～1 361 cm-1）,系列Ⅴ和系列Ⅵ.其中只有系列Ⅲ能改变分子的电偶极矩,该系列振动模式和β相的PVDF的自发极化有着密切的关系.

Vibrational Modes Analysis of Poly (vinylidene fluoride) All-trans Molecular Chain

Ab initio molecular orbital calculation was employed to optimized the geometry structure of poly (vinylidine fluoride) (PVDF) all-trans molecule. The calculated result is consistent with that of experiment. In our calculation, two different values of bond angle C－C－C were found, i.e.112.8° and 113.3°.The infrared intensity spectrum was obtained from frequencies calculation of the all-trans molecule. In the range of 400～4 000 cm－1,the IR spectra of polarized and unpolarized β-phase PVDF film (30 μm thick) have been measured. The calculated IR intensity spectrum is in good agreement with observed IR spectrum. The vibrational modes in the range of 400～4 000 cm－1 were divided into six series, series Ⅰ(544～415 cm－1), series Ⅱ(913～792 cm－1), series Ⅲ(1 353～998 cm－1), series Ⅳ(1 458～1 361 cm－1), seriesⅤand Ⅵ. Only series Ⅲ of all the vibrational modes causes the change of the dipole moment of PVDF molecule, and is related to the spontaneous polarization.