Confirmation of Crystal Structure of Poly(vinylidene fluoride) through the Detailed Structure Analysis of Vinylidene Fluoride Oligomers Separated by Supercritical Fluid Chromatography

Vinylidene fluoride (VDF) oligomers with uniform molecular weights were separated
successfully by using supercritical fluid chromatography, and the crystal structures were determined by
X-ray analysis of the single crystals. Although the chemical formulas of these oligomer components had
not been known clearly, the X-ray structure analysis gave us the following results:  CF(CF3)2−(CH2CF2)n−I with n = 6−12. The oligomer chains were found to form a layer structure, in which the chains
are tilted slightly from the normal to the layer plane. The chain conformation of the oligomers, when
crystallized from ethanol solutions, was a repetition of TGTḠ, essentially the same with that of poly(vinylidene fluoride) crystal form II. The packing structure of central VDF sequence parts was also found
to be the same with that of form II:  the chains are packed in an antiparallel mode with respect to the
chain direction as well as the direction of CF2 dipoles. A series of oligomers were found to show a variety
of crystal modifications depending on the sample preparation conditions, as seen from the infrared spectral
patterns.

采用超临界流体色谱法成功分离得到了分子量均一的偏氟乙烯（Vinylidene fluoride, VDF）低聚物，并通过单晶X射线衍射分析解析了其晶体结构。尽管此前对该类低聚物组分的化学结构式尚不明确，但单晶X射线结构分析得到了如下结果：通式为CF(CF3)2−(CH2CF2)n−I，其中n取值为6~12。研究发现，该低聚物分子链形成层状结构，分子链与层平面法线方向存在轻微倾斜。从乙醇溶液中结晶得到的低聚物，其分子链构象为TGTḠ的重复单元，与聚偏氟乙烯（poly(vinylidene fluoride)）晶型II的构象基本一致。中心VDF序列段的堆积结构也与晶型II一致：分子链沿链方向以及CF2偶极方向均呈反平行排列。通过红外光谱图谱分析可知，该系列低聚物会根据样品制备条件的不同呈现多种晶体晶型变体。