Trifluoroethylene mechanical

Ethylene trifluoroethylene (Tefzel) (ETFE) has good mechanical properties from cryogenic levels to 350°F (177°C). It has an upper continuous working temperature limit of 300°F (149°C). 

The mechanism for reactions of SiF2 with various fluorine derivatives like trifluoroethylene F2C=CHF is similar, yielding l,l-difluoro-2-(trifluorosilyl)-ethane F2C=CFSiF3, l,2-difhioro-l-(trifluorosilyl)ethylene FHC=CFSiF3, and 1,2,2-trifluoro-1 -(trifluorosilyl)ethylene F2C=CFSiF3. 

Polytetrafluoroethylene is the only by-product formed. Trifluoroethylene and 2-chloro- and 2-bromo-l,l-difluoroethylene all react with FIFA regiospecifically to give monohydrooxetanes 2 in 91-98 % yield. The formation of only one isomer, in sharp contrast to the earlier photochemical process [11], is consistent with an electrophilic mechanism (Sch. 2). 

Composites of polypyrrole and poly(vinyl chloride) have been prepared by several groups (64-67). Polythiophene-poly(vinyl chloride) composites have also been prepared (68). The electropolymerization of pyrrole on poly(vinyl chloride)-coated electrodes yielded composites with mechanical properties (tensile strength, percent elongation at break, percent elongation at yield) similar to poly(vinyl chloride) (65) but with a conductivity of 5-50 S/cm, which is only slightly inferior to polypyrrole (30-60 S/cm) prepared under similar conditions. In addition, the environmental stability was enhanced. Morphological studies (69) showed that the polypyrrole was not uniformly distributed in the film and had polypyrrole-rich layers next to the electrode. Similarly, poly(vinyl alcohol) (70) poly[(vinylidine chloride)-co-(trifluoroethylene)] (69) and brominated poly(vinyl carbazole) (71) have been used as the matrix polymers. The chemical polymerization of pyrrole in a poly(vinyl alcohol) matrix by ferric chloride and potassium ferricyanide also yielded conducting composites with conductivities of 10 S/cm (72-74). 

Koga, K. Ohigashi, H. "Piezoelectrisity and related properties of vinylidene fluoride and trifluoroethylene copolymers", J. Appl. Phys., Vol.59, No.6, pp.2142-2150, (1985) Lindner, M., Bauer-Gogonea, S., Bauer, S., Paajanen, M. Raukola, J. "Dielectric barrier microdischarges Mechanism for the charging of cellular piezoelectric polymers", J. Appl. Phys., Vol.91, No.8, pp.5283-5287, (2002)... 

Partially fluorinated materials include ECTFE (ethylene trifluoroethylene), ETEE (ethylene tetrafluoroethylene), and PVDE (polyvinylidene fluoride). The partially fluorinated materials have higher mechanical properties but lower temperature ratings (<300°E/149°C), and chemical resistance. 

It was found that in several polymers, such as stretched and poled poly(vinylidene fluoride) (PVDF) and its copolymer, poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), a strong polarization effect is observed under influence on mechanical stress and temperature. This means that piezoelectric and pyroelectric gas sensors can also be designed based on polymers (see Chap. 13 [Vol. 1]). 

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]. 

Conversely, cases are known where % cycloadditions take place by the ERj mechanism in preference to an alternative allowed Diels-Alder process. A good example is the reaction of butadiene with trifluoroethylene to give the adducts (236)-(239). The fact that (236) and (239) are formed in equal amounts shows that the reaction is not a pericyclic cycloaddition but must take place via the biradical (240). In this the F2C—CFH bond is single, so rotation is possible, the configuration of the original reactants being lost. Even the 13% of normal Diels-Alder product may be, and probably is, formed by cyclization of the same intermediate biradical, either (240) or the precursor (241) of (238). 

Kawai s (7) pioneering work almost thirty years ago in the area of piezoelectric polymers has led to the development of strong piezoelectric activity in polyvinylidene fluoride (PVDF) and its copolymers with trifluoroethylene and tetrafluoroethylene. These semicrystalline fluoropolymers represent the state of the art in piezoelectric polymers. Research on the morphology (2-5), piezoelectric and pyroelectric properties (6-70), and applications of polyvinylidene fluoride 11-14) are widespread in the literature. More recently Scheinbeim et al. have demonstrated piezoelectric activity in a series of semicrystalline, odd numbered nylons (75-77). When examined relative to their glass transition tenq>erature, these nylons exhibit good piezoelectric properties (dai = 17 pCTN for Nylon 7) but have not been used commercially primarily due to the serious problem of moisture uptake. In order to render them piezoelectric, semicrystalline polymers must have a noncentrosynunetric crystalline phase. In the case of PVDF and nylon, these polar crystals cannot be grown from the melt. The polymer must be mechanically oriented to induce noncentrosynunetric crystals which are subsequently polarized by an electric field. In such systems the amorphous phase supports the crystalline orientation and polarization is stable up to the Curie temperature. 

The same authors developed an original method of the synthesis of 1-(1,2,2,2-tetrafluoroethyl)-l,2,4-triazole 85 by treatment of N-(2-chloro-l,l,2-trifluoro)-1,2,4-triazole with tetramethylammonium fluoride [83]. The assumed reaction mechanism consist of several steps. In the first stage elimination of HF and the formation of 2-chloro-l,2-difluoroethylene derivative takes place. Further chlorine atom is replaced by fluorine with the formation of 1,2,2-trifluoroethylene-l,2.4-triazole. Finally addition of HF gave the final product 85. 

Bharti Vet al (1999) High electrostrictive strain under high mechanical stress in electron irradiated poly(vinylidene fiuoride-trifluoroethylene) copolymer. Appl Phys Lett 75 2653... 

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. 

Another widely used approach is the in situ polymerization of an intractable polymer such as polypyrrole onto a polymer matrix with some degree of processibil-ity. Bjorklund [30] reported the formation of polypyrrole on methylcellulose and studied the kinetics of the in situ polymerization. Likewise, Gregory et al. [31] reported that conductive fabrics can be prepared by the in situ polymerization of either pyrrole or aniline onto textile substrates. The fabrics obtained by this process maintain the mechanical properties of the substrate and have reasonable surface conductivities. In situ polymerization of acetylene within swollen matrices such as polyethylene, polybutadiene, block copolymers of styrene and diene, and ethylene-propylene-diene terpolymers have also been investigated [32,33]. For example, when a stretched polyacetylene-polybutadiene composite prepared by this approach was iodine-doped, it had a conductivity of around 575 S/cm and excellent environmental stability due to the encapsulation of the ICP [34]. Likewise, composites of polypyrrole and polythiophene prepared by in situ polymerization in matrices such as poly(vinyl chloride), poly(vinyl alcohol), poly(vinylidine chloride-( o-trifluoroethylene), and brominated poly(vi-nyl carbazole) have also been reported. The conductivity of these composites can reach up to 60 S/cm when they are doped with appropriate species [10]. 

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