Trifluoroethylene mechanical processing

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). 

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). 

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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