Trifluoroethylene structure

In the article by Balta Calleja et al., the latest results of investigations into the structure of poly(vinylidenefluoride)and its copolymers withpoly(trifluoroethylene) are summarized and extensively dicussed. These polymers are the most important ferroelectric materials. Special emphasis is placed on the relation between the change of structure and the transition from the ferroelectric into the paraelectric phase. 

Poly(chloro trifluoroethylene) is another macromolecule which can, at pressures as little as 10 MPa, be crystallized into extended chain crystals139). Little is known about the detailed process, but a high mobility state was assumed to explain the special crystallization 19). The only crystal structure reported is hexagonal with 17 monomers in the repeat distance along the chain axis. Conditions for conformational mobility seem favorable. 

According to this literature survey, most investigations have been performed photochemically and in most cases, the monoadduct is composed of two isomers, the ratio of which depends upon the electrophilicity of the telogen radical. In the case of fluoroalkyl iodides, such an olefin exhibits the same reactivity towards these telogens, whatever their structure. In addition, trifluoroethylene seems less reactive than vinylidene fluoride but more reactive than hexafluoro-propene. 

Trifluoroethylene reacts with 1,3-butadiene to give three compounds, R, S, and T. What are their structures, and how are they formed ... 

The majority of vinyl polymers are regioregular with a head-to-tail sequence of monomer units (0, i.e. they are isoregic (2). Some of the most notable exceptions are the polymers obtained by free-radical addition reactions of the fluoroethylenes vinyl fluoride (VF), vinylidene fluoride (VF2), and trifluoroethylene (F3E), which incorporate significant amounts of head-to-head and tail-to-tail structural defects caused by reverse monomer addition (3). 

Tashiro K, Takano K, Kobayashi M, Chatani Y, Tadokoro H (1981) Structural study on ferroelectric phase transition of vinylidene fluoride-trifluoroethylene random copolymers. Polymer, 22 1312 25 195 (1984)... 

A copolymer of vinylidene fluoride-trifluoroethylene (VDF/TrFE) copolymer is well known as the polymer for which a clear Curie point was found for the first time in an organic material. At this Curie point, the polymer undergoes a solid-to-solid phase transition from paraelectric to ferroelectric phases with decreasing temperature. Therefore, the changes in the physical properties such as crystal structure, electrical and thermal properties upon the ferroelectric phase transition have drawn many researchers interest. Here, the results concerning the ultrasomc spectroscopic mvestigation on acoustic and viscoelastic behaviour around the ferroelectric phase transition region of this copolymer are described [15]... 

Hayashi, K., TsubaJdhara, H., Kubo, U. Doping effect on the electric current and molecular structure of a vinylidenefluoride-trifluoroethylene copolymer. Japanese Journal of Applied Physics 36, 1176-1177 (1997)... 

In the addition to homo-PVF2, a large number of copolymers have also been synthesized which allow to optimize the mechanical properties of fluoropolymers. Most common are copolymers with vinyl fluoride, trifluoroethylene, tetrafluoroethylene, hexafiuoropropy-lene, hexafluoroisobutylene, chlorotrifluoroethylene, and pentafiuoro-propene [521,535, 559-562]. Copolymerization with nonfluorinated monomers is possible [563] in principle but has not yet found commercial use. Fluorocarbon monomers that can help to retain or enhance the desirable thermal, chemical, and mechanical properties of the vinylidene structure are more interesting comonomers. Copolymerization with hexafluoropropylene, pentafluoropropylene, and chlorotrifluoroethylene results in elastomeric copolymers [564]. The polymerization conditions are similar to those of homopoly(vinylidene fluoride) [564]. The copolymers have been well characterized by x-ray analysis [535], DSC measurements [565], and NMR spectroscopy [565,566]. 

Huang et al (2004) Poly(vinylidene floride-trifluoroethylene) based high performance electroactive polymers. IEEE Trans Dielec Elec Insul 20 299-311 Jayasuriya et al (2001) Crystal-structure dependence of electroactive properties in differently prepared poly(vinylidene fluoride/hexafluoropropylene) copolymer films. J Polym Sci Part B Polym Phys 39(22) 2793-279... 

The results for the trifluoroethylene copolymer suggests that structural isomerism should indeed be detectable by ESCA. In view of this, deconvolutions may be attempted for the trifluoro- and chlorotrifluoro-ethylene copolymers using five individual peaks with lineshape and linewidth corresponding to that for the p3 Cis levels. The five peaks in each case corresponding to four CP2 and CFX carbons, (in two pairs corresponding to the two distinct modes of bonding) and only one for the CP3 carbon. 

As discussed previously in the section on primary batteries, an acrylate is often used as a crosslinkable monomer to form a polymer matrix for a nonaqueous electrolyte. The salt-in-polymer type polymer electrolyte made by dissolving trifluoroethylene glycol methacrylate into methoxy poly(ethylene glycol methacrylate) forms a comb-like network structure at the covalently bonded portion. The ethylene oxide chain consists of 22 monomer units, and the ionic conductivity at room temperature is reported to be 10 S/cm. If sodium thiocyanate is used [30] instead of lithium trifluoromethane sulfonate, the ionic conductivity reduced to 10 S/cm. However, by adding 50 wt% of PC as a plasticizer, the ionic conductivity reaches 10 " S/cm. 

The chain confonnidon of poly(trifluoroethylene) (PTrFE) crystal was first reported by Lando et iL to be a 3/1 helix [1). Tashiro et have studied the structure and ferroelectric transitioas of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) co-polymers and concluded that the crystal structure of PTVFE is the same as the cooled phase which has the all-trans conformation with skew bonds [2]. The latter structural mixiel permits the formatioa of the spontaneous polarization in TVFE. Lovlnger et al. carried out X-ray measurements on PTrFE and proposed the confoimation of an irregular succession TO. TC. and TT from the lattice spacing parallel to the carbon chain [3]. 

Investigations in the 1970s were extended to include copolymers of vinylidene fluoride (VDF) with related fluorinated vinyl monomers vinyl fluoride (VF), trifluoroethylene (TrFE) and tetrafluoroethylene (TeFE) [7, 8]. The latter two copolymers were found to crystallize into polar form without the stretching stage required by PVDF. This facilitates processing, and thus offers a wider range of potential device structures. Research in the 1980s has therefore focused on the ferroelectric behaviour and piezoelectric activity of vinylidene fluoride-trifluoroethylene copolymers. 

Polymerization of the fluoro monomers is carried out at temperatures in the range 20-60 °C and at pressures up to 60 MPa. Even in the case of the simple self-addition of vinyl fluoride molecules, the precise reaction conditions have a significant effect on the detailed structure of the resulting polymer. Because the molecules are not symmetrical, they can link to each other in the chain in three possible ways. These are the normal, and energetically favourable, head-to-taiT configuration (producing electrically inactive material) or the so-called defect combinations of head-to-head and tail-to-taiT [8]. The effect of the tow fraction of these defects present in the poly(vinylidene fluoride) prepared by standard routes is small, and the polymer crystallizes from the melt in a non-polar form. In contrast to this, polymerization of a mixture of vinyl fluoride and trifluoroethylene monomers results in many head-to-head sequences, the effect of which causes the polymer to crystallize in a potentially active form, a structure only attainable in poly(vinylidene fluoride) by vigorous mechanical reorientation. 

Copolymers of PVDF with trifluoroethylene are semicrystaUine systems in which the crystalline part exhibits ferroelectricity. For TrFE molar fractions below 85 %, this crystalline phase suffers a phase transition below the melting point. TrFE units are included in the unit cell of PVDF and enlarge it since they are bulkier. This enlargement weakens the intermolecular interactions among chains, and destabilizes the ferroelectric phase with the all-trans conformation. The more TrFE segments in the chain, the more unstable the ferroelectric phase becomes. As a direct consequence, the ferroelectric-to-paraelectric Curie transition temperature decreases with the increase of TrFE units [24]. This change in the crystalline structure, from... 

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