偏氟乙烯／三氟乙烯共聚物介电松弛的结晶度效应

用改进的介电松弛谱仪（精度２‰）测定了ＶＤＦ／ＴｒＦＥ（７／２７、６５／３５、５２／４８ｍｏｌ％）共聚物溶液成膜、液氮淬火、熔融慢冷和热处理试样在－１２０—１３０℃、１０－２一１０４Ｈｚ范围的复数介电常数．介电松弛研究结果显示低结晶度的淬火试样较高结晶度的熔融慢冷和热处理试样的Ｔｃ高．结晶度上升，居里点处的介电常数增大．室温以下的介电频率谱分别由代表非晶区分子运动的β松弛（低频部）和局域运动的γ松弛（高频部）叠合而成．随结晶度提高，β松弛峰减小，γ松弛峰增大；非晶松弛强度减弱．晶区松弛强度增强．     

高温热处理对偏氟乙烯-四氟乙烯共聚物高次结构的影响

The effect of high temperature annealing on the higher order structure of a copolymer of vinylidene fluoride and tetrafluoroethylene (TFE 2.8 mol %) has been studied by various method, primarily dynamic mechanical, by also dielectric and microspic. The controversy on the origin of a relaxations is discussed from the point of view of higher order structure studies.     

高温热处理对偏氟乙烯-四氟乙烯共聚物高次结构的影响

聚偏氟乙烯(PVDF)及其一些共聚物,例如偏氟乙烯-四氟乙烯共聚物(PVDF/TFE)经过处理后呈现较强的压电性。许多研究表明它们是铁电聚合物,而且压电活性与样品的高次结构有关。松弛谱是研究结晶高聚物的高次结构的有力工具,近来,Koizumi等人报道了PVDF/TFE的热处理与松弛现象的关系。本文作者也报道了     

钛酸铅与偏氟乙烯-三氟乙烯共聚物形成的铁电复合物相变过程的热释电研究

研究了偏氟乙烯-三氟乙烯共聚物与钛酸铅形成的铁电复合物PT/P[VDF(70)-TrFE(30)]的热释电流行为。P[VDF(70)-TrFE(30)]室温下存在两个铁电相,即较无序的铁电相和较有序的铁电相,升温经过各自的相转变点后转变成较有序的顺电相和较无序的顺电相。热释电流谱上出现在95℃和108℃的两个电流峰,分别由两个铁电相的结构陷阱以及部分取向的偶极所贡献。采用Tc以上温度极化并冷却到不同温度的方法可明确鉴别出该试样两个顺电相降温转变过程,转变点分别为62℃和50℃。实验证实陷阱仅存在于铁电相而不存在于顺电相中。钛酸铅的引入虽不导致新电流峰出现,但可使共聚物的Tc降低、电流加大。热释电流方法可非常灵敏地跟踪铁电共聚物的相变过程。     

偏氟乙烯-三氟氯乙烯共聚物链结构的研究

用裂解气相色谱-质谱法(Py-GC/MS)研究了单体克分子比近于1:1的偏氟乙烯-三氟氯乙烯共聚物(F23)链结构。采用了居里点裂解器和裂解探针。质谱的鉴定结果表明,两种裂解器在一定条件下得到的F23裂解产物非常相似。根据这些裂解产物的化学结构,可以推断F23中两种单体的键接方式,并确定F23中占优势的链段排列为:(?)     

偏氟乙烯/三氟氯乙烯无规共聚物的结晶

用示差扫描量热法(DSC)、广角X射线衍射(WAXD)和傅里叶红外光谱(FTIR)研究了偏氟乙烯/三氟氯乙烯单体摩尔比为1:4的无规共聚物的结晶与晶体结构.结果表明,该无规共聚物属于半结晶型聚合物.在333～353K温度范围内退火,片晶逐渐完善、增厚,熔点和结晶度均随着退火时间的延长而升高.于353K退火时,由DSC结果计算得到片晶厚度约4.68nm.在333K退火时得到共聚物的最大结晶度约为14%.WAXD测试结果表明,沿晶粒(101)晶面的面间距为0.55nm,垂直于(101)衍射晶面方向上的晶粒平均尺寸为5.86nm.     

偏氟乙烯-四氟乙烯共聚物的β、γ混合晶型固相转变与松弛现象

本文用红外光谱及压电常数方法研究了偏氟乙烯-四氟乙烯共聚物在高压直流电场下,γ晶型向β晶型的固相转变。同时用动态力学方法、介电损耗测试法及压电常数方法研究了样品的松弛现象。     

偏氟乙烯-六氟丙烯共聚物基微孔-凝胶聚合物电解质的研究进展

综述了近年来偏氟乙烯-六氟丙烯共聚物[poly(vinylidenefluoride-co-hexafluoropropylene),P(VDF-HFP)]基微孔-凝胶聚合物作为锂离子电池聚合物电解质的研究进展,内容包括该类聚合物电解质的制备方法及其改性,并展望了其发展趋势.随着技术的进一步发展,完全可以制备出性能优良的聚合物锂离子电池.     

Symmetric Ferroelectric Switching in Ferroelectric Vinylidene Fluoride and Trifluoroethylene Copolymer Films

We report the observation of asymmetric switching dual peaks in ferroelectric copolymer films. These dual peaks occurs when the poling electric field is just below the coercive field and can be removed by continuous application of high enough switching voltage. Our experimental observations can be explained by the injection and the redistribution of space charges in ferroelectric films.     

偏氟乙烯-四氟乙烯共聚物热释电性的研究

本实验室合成了一系列不同组成的偏氟乙烯-四氟乙烯共聚物(F_(24)),并通过浇铸与极化制成了热电薄膜. 实验结果表明F_(24)薄膜的热释电系数依赖于极化温度,极化电场,极化时间。选用适当的极化条件可以提高薄膜的热释电性。热释电系数还与共聚物组成有关,当共聚物中,偏氟乙烯的克分子百分数为80～85时,热释电系数最高.此外,还测定了F_(24)的电滞回线。     

Unexpected Radical Telomerisation of Vinylidene Fluoride with 2-Mercaptoethanol

The radical telomerisation of vinylidene fluoride (VDF) with 2-mercaptoethanol as chain transfer agent (CTA) was studied to synthesise fluorinated telomers which bear a hydroxy end-group, such as H(VDF)_nS(CH₂)₂OH, under thermal (di-tert-butyl peroxide as the initiator) or photochemical initiations. A careful structural study of a typical H-VDF-S(CH₂)₂OH telomer was performed by ¹H and ¹⁹F NMR spectroscopy. These analytical methods allowed us to explore the selective addition of the thiyl radical onto the hydrogenated side of VDF, and the telomer containing one VDF unit was obtained selectively. Surprisingly, for higher [VDF]_o initial concentrations, a monoadduct telomer was produced as well as PVDF homopolymer. This feature was related to the fast consumption of the CTA. The kinetics of radical telomerisation led to a quite high transfer constant of the CTA (40 at 140 °C) that evidences the formation of a monoadduct as the only telomer formed.     

铁电共聚物VDF／TrFE的低温低频介电松弛

在低温低频下用介电松弛方法研究了液氮淬火，熔融慢冷和热处理结晶铁电共聚物ＶＤＦ（７３）／ＴｒＦＥ（２７）的分子运动特征，随结晶度升高，居里点温度降低，铁电－顺电相变区的介电常数增大。室温以下共聚物的频率谱由低频和高频两部分组成。低频部由非晶工区被冻结分子链段的微布朗运动贡献。高频部则由晶区和非晶区分子链段较小尺度的局域运动产生。由两个Ｃｏｌｅ－Ｃｏｌｅ函数对频率谱进行分峰拟合并根据ＷＬＦ方程和Ａｒ     

偏氟乙烯分散聚合的成核及初级粒径

以分散聚合的相关成核理论为基础,采用核磁共振（19F-NMR）和傅里叶红外分析（FT-IR）等分析方法研究了偏氟乙烯（VDF）分散聚合的成核机理,并确认了以低聚物成核机理为其主要形式。同时,通过实验确定了PVDF乳胶粒粒径（d）与转化率（X）、反应压力（p）、初始引发剂质量浓度（ρI,0）以及初始乳化剂质量浓度（ρS,0）有着如下关系：d∝X0.36 p1.20ρI-,00.76ρS-,00.33。在各个因素中,反应压力（或单体质量浓度）的影响程度最大。     

合成偏氟乙烯和含氟丙烯的催化剂及应用研究进展

由于含氟烯烃在自然界易降解、对臭氧层破坏力小、对环境友好的特性,近年来在科研和工业领域得到广泛关注.偏氟乙烯（VDF）和含氟丙烯是重要的含氟烯烃,主要用于合成氟弹性体高分子功能材料的单体和含氟树脂等.我们参照偏氟乙烯的合成发展史,主要介绍了通过催化,热裂解和共裂解方法合成偏氟乙烯过程中使用的催化剂类型、工艺条件和结果对比,综述了近年来偏氟乙烯的主要合成方法,并介绍了通过直接催化氟化法合成含氟丙烯的工艺技术及其可能机理研究进展.     

Homogeneous Phase Copolymerizations of Vinylidene Fluoride and Hexafluoropropene in Supercritical Carbon Dioxide

Copolymerizations of vinylidene fluoride (VDF) and hexafluoropropene (HFP) were carried out in homogeneous phase with supercritical carbon dioxide up to complete VDF conversion using conventional peroxide initiators. The HFP monomer feed ratios, f_HFP, were varied between 0.65 and 0.20. Depending on f_HFP amorphous or semi‐crystalline copolymers were obtained. f_HFP also determines the minimum pressure required to allow for homogeneous phase reactions. For example, HFP‐rich copolymerizations in 70 wt.‐% CO₂ at 100 °C require a pressure of around 500 bar. Further, bulk copolymerizations in homogenous phase were feasible for f_HFP = 0.65 at 900 bar up to complete VDF conversion. Copolymerizations in the presence of perfluorinated hexyl iodide carried out at 75 °C gave access to low dispersity polymers. Due to homogeneous phase conditions the use of any surfactants or fluorinated cosolvent is avoided.

     

Novel Source of Trifluoromethyl Radical As Efficient Initiator for the Polymerization of Vinylidene Fluoride

A persistent perfluoroalkyl radical (PPFR), perfluoro‐3‐ethyl‐2,4‐dimethyl‐3‐pentyl, is shown to be a good source of •CF₃ radicals and a useful radical capable of initiating the polymerization of vinylidene fluoride (VDF). NMR characterizations of the resulting PVDF homopolymers showed that polymerization of VDF was exclusively initiated by •CF₃ radicals. The addition of •CF₃ radical onto VDF was regioselective leading to CF₃‐CH₂‐CF₂‐PVDF and the CF₃ end‐group acted as an efficient label to assess the molecular weights by ¹⁹F NMR spectroscopy. Various [PPFR]₀/[VDF]₀ initial molar ratios lead to CF₃–PVDF–CF₃ of different molecular weights. When that ratio decreased, both the molecular weights and the thermostability of these PVDFs increased, showing less defects of chaining and higher crystallinity.     

Evaluation of piezoelectric poly(vinylidene fluoride) polymers for use in space environments. I. Temperature limitations

Smart materials, such as thin‐film piezoelectric polymers, are interesting for potential applications on Gossamer spacecraft. This investigation aims to predict the performance and long‐term stability of the piezoelectric properties of poly(vinylidene fluoride) (PVDF) and its copolymers under conditions simulating the low‐Earth‐orbit environment. To examine the effects of temperature on the piezoelectric properties of PVDF, poly(vinylidenefluoride‐co‐trifluoroethylene), and poly(vinylidenefluoride‐co‐hexafluoropropylene), the d₃₃ piezoelectric coefficients were measured up to 160 °C, and the electric displacement/electric field (D–E) hysteresis loops were measured from ?80 to +110 °C. The room‐temperature d₃₃ coefficient of PVDF homopolymer films, annealed at 50, 80, and 125 °C, dropped rapidly within a few days of thermal exposure and then remained unchanged. In contrast, the TrFE copolymer exhibited greater thermal stability than the homopolymer, with d₃₃ remaining almost unchanged up to 125 °C. The HFP copolymer exhibited poor retention of d₃₃ at temperatures above 80 °C. In situ D–E loop measurements from ?80 to +110 °C showed that the remanent polarization of the TrFE copolymer was more stable than that of the PVDF homopolymer. D–E hysteresis loop and d₃₃ results were also compared with the deflection of the PVDF homopolymer and TrFE copolymer bimorphs tested over a wide temperature range. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1310‐1320, 2005     

Homogeneous Phase Polymerization of Vinylidene Fluoride in Supercritical CO2: Surfactant Free Synthesis and Kinetics

Summary: Vinylidene fluoride (VDF) polymerizations were carried out in homogeneous phase with supercritical carbon dioxide (scCO₂) at 120 °C and 1500 bar. To control molecular weight perfluorohexyl iodide was used. Molecular weight analysis by size-exclusion chromatography indicates that polymers of low polydispersities ranging from 1.5 to 1.2 at the highest iodide concentration of 0.25 mol · L⁻¹ were obtained. In addition, polymer molecular weight increases linearly with reaction time, indicating that living conditions were established. The “livingness” is based on the labile C-I bond. The weakness of the C-I bond is associated with a fast decomposition of the original hexyl iodide, thus, contributing to initiation and to a significant increase in the initiation rate in the initial phase of the polymerization.