Polymers benzene oxidation route

Thiophene, pyrrole and their derivatives, in contrast to benzene, are easily oxidized electrochemically in common solvents and this has been a favourite route for their polymerization, because it allows in situ formation of thin films on electrode surfaces. Structure control in electrochemical polymerization is limited and the method is not well suited for preparing substantial amounts of polymer, so that there has been interest in chemical routes as an alternative. Most of the methods described above for synthesis of poly(p-phenylene) have been applied to synthesise polypyrrole and polythiophene, with varying success. 

Combining whole-cell biocatalysis and radical polymerization, researchers at Imperial Chemical Industries (ICI) published a chemoenzymatic route to high-molecular-weight poly(phenylene) [86], This polymer is used in the fibers and coatings industry. However, since it is practically insoluble, the challenge was to make a soluble polymer precursor that could first be coated or spun, and only then converted to poly(phenylene). The ICI process starts from benzene, which is oxidized by Pseudomonas putida cells to cyclohexa-3,5-diene-l,2-diol (see Figure 5.17). The... 

Polymers with pendant carbodiimide groups 27 are also synthesized from crossUnked polystyrene. In this synthetic route crossUnked polystyrene beads are chloromethylated and converted to the amines. Reaction with isopropyl isocyanate gives the corresponding ureas, which are treated with tosyl chloride and triethylamine to produce the crossUnked polycarbodiimides. This polymer is used in the polymer supported Moffatt oxidation of alcohols into aldehydes or ketones using benzene/DMSO. ... 

To obtain soluble PPP homopolymers, two main strategies have been used. The first is the so-called precursor route. It consists in starting from soluble materials that are chemically or thermally converted into fully aromatic polymers by elimination of leaving groups. An example is the precursor route utilized by Ballard et al. [89] (Fig. 9.8). Synthesis is based on 5,6-cz s-dihydroxycyclohexa- 1,3-diene as starting material and originating from the bacterial oxidation of benzene by Pseudomonas... 

The substitution of the aromatic backbone ring by alkylphenyl groups is helpful to get soluble PPX types. The polymer synthesis using these monomers can proceed in a THF, dioxane, or benzene solution. The polymer is formed by a dehydrochlorination reaction using tert-butyl oxide. The synthesis is shown in Figure 2.4. The dehydrohalogenation reaction is also referred to as the Gilch route. 

The previous studies of the reactions of polymeric organo-lithium compounds with epoxides suggested that these reactions might provide a facile route to a variety of functionalized polymers by attaching other substituents to the epoxide ring. Therefore, the functionalization of PSLi with styrene oxide was investigated. If this functionalization were efficient, a variety of substituents and more than one substituent at a time could be placed on the benzene ring of styrene oxide to form a variety of functionalized polymers as shown in eqn [9]. 

Films of PPP have to be prepared via precursor routes (previously reviewed by Gin and Conticello [36]). The route most often used to prepare films of PPP (1) is one developed at ICI (Scheme 3) [37,38]. This starts with a microbial oxidation of benzene to cyclohexadienediol 6. Radical-initiated polymerisation of the diacetate 7 gives the precmsor polymer 8, which is then thermally converted to 1. However, the material is not stereoregular as it contains about 10-15% of 1,2-linkages. This material has been used by Leising et al. to prepare blue-emitting LEDs (A,max = 459 nm) with efficiencies of up to 0.05% [39-41]. 

By far the largest outlet for benzene (approx. 60%) is styrene (phenyl-ethene), produced by the reaction of benzene with ethylene a variety of liquid and gas phase processes, with mineral or Lewis acid catalysts, are used. The ethylbenzene is then dehydrogenated to styrene at 600-650°C over iron or other metal oxide catalysts in over 90% selectivity. Co-production with propylene oxide (section 12.8.2) also requires ethylbenzene, but a route involving the cyclodimerization of 1,3-butadiene to 4-vinyl-(ethenyl-) cyclohexene, for (oxidative) dehydrogenation to styrene, is being developed by both DSM (in Holland) and Dow. 60-70% of all styrene is used for homopolymers, the remainder for co-polymer resins. Other major uses of benzene are cumene (20%, see phenol), cyclohexane (13%) and nitrobenzene (5%). Major outlets for toluene (over 2 5 Mt per annum) are for solvent use and conversion to dinitrotoluene. 

Ethylene from cracking of the alkane gas mixtures or the naphtha fraction can be directly polymerized or converted into useful monomers. (Alternatively, the ethane fraction in natural gas can also be converted to ethylene for that purpose). These include ethylene oxide (which in turn can be used to make ethylene glycol), vinyl acetate, and vinyl chloride. The same is true of the propylene fi action, which can be converted into vinyl chloride and to ethyl benzene (used to make styrene). The catalytic reformate has a high aromatic fi action, usually referred to as BTX because it is rich in benzene, toluene, and xylene, that provides key raw materials for the synthesis of aromatic polymers. These include p-xylene for polyesters, o-xylene for phthalic anhydride, and benzene for the manufacture of styrene and polystyrene. When coal is used as the feedstock, it can be converted into water gas (carbon monoxide and hydrogen), which can in turn be used as a raw material in monomer synthesis. Alternatively, acetylene derived from the coal via the carbide route can also be used to synthesize the monomers. Commonly used feedstock and a simplified diagram of the possible conversion routes to the common plastics are shown in Figure 2.1. 

Development of xanthate and dithiocarhamate derivatives overcomes several drawbacks of the sulfonium monomer (Scheme 7.2b and c). Xanthates and dithiocarbamates are easily prepared by the reaction of bis(halomethyl)benzene with alkylxanthate and dialkyldithiocarbamate salts respectively. Both precursors are stable at room temperature and soluble in organic solvents. This means the polymerization of these monomers can be performed in organic solvents e.g. THE) with the addition of alkoxide base e.g. potassium tert-butoxide). For the dithiocarhamate precursor, lithium bis(trimethylsilyl)amide can be used as the base and the polymerization proceeds at 35 The elimination temperature of these precursor polymers is typically lower than that of the sulfonium polymers with xanthate elimination at 160-250 °C and dithio-carbamate at 180 °C. It has been found that elimination of dithiocarbamate gave materials with reduced structural defects. Both xanthate and dithiocarbamate routes avoid the corrosive acid byproducts (HCl) present in the sulfonium elimination. This is particularly advantageous in device fabrication as adds have a negative impact on indium tin oxide electrodes and interfaces. ... 

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