Polymerization of benzene

Polyacetylene has good inert atmospheric thermal stability but oxidizes easily in the presence of air. The doped samples are even more susceptible to air. Polyacetylene films have a lustrous, silvery appearance and some flexibility. Other polymers have been found to be conductive. These include poly(p-phenylene) prepared by the Freidel-Crafts polymerization of benzene, polythiophene and derivatives, PPV, polypyrrole, and polyaniline. The first polymers commercialized as conductive polymers were polypyrrole and polythiophene because of their greater stability to air and the ability to directly produce these polymers in a doped form. While their conductivities (often on the order of 10" S/m) are lower than that of polyacetylene, this is sufficient for many applications. 

One of the earliest attempts to synthesize heat-resistant polymers was the oxidative polymerization of benzene to poly(p-phenylene) [IUPAC poly(l,4-phenylene)] (Eq. 2-227) [Jones... 

Peroxynitrite is capable of initiating many of the reactions commonly attributed to hydroxyl radical, particularly under acidic conditions. Halfpenny and Robinson (1952a,b) showed that nitrous acid plus hydrogen peroxide in aqueous solutions at pH 2, which generates peroxynitrous acid, initiated the polymerization of methylmethacrylate (the precurser to Plexiglas) as well as the hydrox-ylation, nitration, and polymerization of benzene. 

Direct polymerization of benzene through oxidative coupling yields polytp-phenylene) (PPP) an insoluble polymer of low molecular weight.427-429 Kovacic s original synthesis430 using a Lewis acid-oxidant combination [Eq. (13.81)] is the most widely employed and still the most effective procedure for the synthesis of PPP ... 

Fig. 3 a and b. Proposed mechanisms for the polymerization of benzene by the Kovacik route... 

Kovacic P, Kyriakis A. Polymerization of benzene to p-polyphenyl by aluminum chloride-cupric chloride. J Am Chem Soc 1963 85 454-458. 

The polymerization of benzene in chloroaluminate salts has attracted attention from a number of authors. The electrosynthesis of this polymer is highly desirable but challenging, with one of the primary considerations being the strict elimination of water from the reaction medium, which is most commonly effected using difficult systems such as liquid sulfur dioxide, concentrated sulfuric acid or HF. The polymerization of benzene and biphenyl in organic solvents yields only low conductivity films with low degrees of polymerization. 

Another mechanism has been proposed for the oxidative polymerization of benzene in HF/SbFs in the presence of an applied potential [312]. In this proposed mechanism, the coupling step occurs after protonation... 

Alberty, R. A., Kinetics and equilibrium of the polymerization of benzene series aromatic hydrocarbons in a flame. In Kinetic and Thermodynamic Lumping of Multicomponent Mixtures. (As-tarita, G., and Sandler, R. I., eds.), Elsevier, Amsterdam, 1991, p. 277. 

Figure 34.13 Reverse osmosis characteristics of composite membranes prepared by plasma polymerization of benzene/H20/N2 compared with those from acetylene/H20/ N2 represented by the solid line porous polysulfone film as the substrate, 3.5% NaCl at 1500 psi.

As in the case of ethylene and acetylene W, plasma polymerization of benzene produced either a powder or film depending on reaction conditions. A typical condition in which thin film with the required property was produced (the RO membrane condition) is shown in Table 1, coded as Condition B, while that for poor quality film formation is designated A. Conditions for powder formation are designated C and E in the table. Generally speaking, film formation was observed at high benzene flow rates, and powder formation was observed at low pressures and low benzene flow rates, as in the case of ethylene and acetylene ( ). However, the RO membrane conditions do not correspond to either a unique point on the pressure (P) versus benzene flow rate (Q(Bz)) plane nor do they correspond to the conditions in which a lot of polymer was produced. This means that the quality of the film cannot be correlated directly to the macroscopic reaction conditions. 

Polymers in this category are of interest in that they can be easily synthesized, being of very high stability. A couple of these polymers are illustrated in Fig. 16. Poly(p-phenylene) is prepared by the polymerization of benzene with A1C13 and CuCl2 (Kovacic and Kyriakis, 1963 Kovacic and Oziomek, 1964), whereas polypyrrole and polythienylene are prepared by the electrochemical polymerization of each monomer with an appropriate electrolyte (Diaz et al., 1979 Tourillon and Gamier, 1982). Polythienylene is also synthesized by the polycondensation of dihalo-thiophene (Yamamoto et al., 1980). 

The polymer that results when benzene is reacted with the powerful oxidizers 02+ and C6F6+ is readily oxidized by AsF5 (13,14). (AsF5, although not capable of initiating the polymerization of benzene, can polymerize the more easily oxidized phenylene oligomers, including biphenyl). 

The acidic ionic liquid [NBPY]Q-AlCl3 (X(A1C13) = 0.67) has been used as a solvent for the electrochemical polymerization of benzene to PPP as conductive films which were flexible and transparent. The films were prepared with very... 

This polymer is completely aromatic in character. Polymerization of benzene to polyphenylene was therefore investigated quite thoroughly. Benzene and other aromatic... 

Scheme 13.1 Stoichiometry of the oxidative polymerization of benzene under Kovacic conditions.

The direct polymerization of benzene is definitely one route that can be followed. This technique was developed by Kovacic and others in the 1960s... 

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