For several decades, poly(1,2-difluoroethylene) [PVLF, −(CHFCHF)_n−] had been believed to be atactic and amorphous. However, our recent study has revealed that PVLF is an atactic but partially crystalline polymer. In the present report, the crystal structure of PVLF, as the most important basic structural information, was determined by the quantitative analysis of 2D wide-angle X-ray diffraction (WAXD) data measured at room temperature. The two chains pass through the orthorhombic unit cell of a = 9.20 Å, b = 5.32 Å, c (chain axis) = 4.97 Å with the space group Pcam. The polymer chains take the deflected zigzag conformation of TS′TS̅′ (torsional angles, T: 180° and S′: 142°), which is contracted slightly from the fully extended all-trans form. The temperature-dependent measurement of the WAXD patterns revealed that the unit cell size increases almost linearly with temperature but shows a small deflection point at around 100 °C. This deflection corresponds to the reversible second-order phase transition between the low-temperature (LT) phase and the high-temperature (HT) phase. The molecular dynamics calculation revealed an occurrence of the thermally activated translational and torsional motion of molecular chains in the HT phase. In parallel, temperature-dependent small-angle X-ray scattering data analysis revealed that the lamellar stacking structure changes irreversibly at the transition point as a result of such thermally enhanced motions of molecular chains.

中文翻译：

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聚(1,2-二氟乙烯)的晶体结构和相变行为


几十年来，聚（1,2-二氟乙烯）[PVLF, -(CHFCHF) _n -]一直被认为是无规立构和无定形的。然而，我们最近的研究表明，PVLF 是一种无规立构但部分结晶的聚合物。在本报告中，PVLF的晶体结构作为最重要的基本结构信息，是通过对室温下测量的二维广角X射线衍射（WAXD）数据进行定量分析来确定的。两条链穿过正交晶胞a = 9.20 Å、 b = 5.32 Å、 c （链轴）= 4.97 Å，空间群为Pcam 。聚合物链呈现偏转之字形构象TS′TS̅′（扭转角，T：180°和S′：142°），该构象从完全延伸的全反式稍微收缩。 WAXD 图案的温度依赖性测量表明，晶胞尺寸几乎随温度线性增加，但在 100 °C 左右显示出一个小偏转点。这种偏转对应于低温（LT）相和高温（HT）相之间的可逆二级相变。分子动力学计算揭示了HT相中分子链发生热激活的平移和扭转运动。同时，与温度相关的小角度 X 射线散射数据分析表明，由于分子链的这种热增强运动，层状堆积结构在转变点发生不可逆变化。