Poly aromatic hydrocarbon formation

By comparing the results for chlorinated polypropylene with those for polypropylene, it can be concluded that the two materials undergo very different pyrolytic reactions. Typical for polypropylene is the formation of fragments of the polymeric backbone with formation of monomer, dimer, etc., or with cleavage of the backbone in random places and formation of compounds with 3n, 3n-1, and 3n+1 carbon atoms (see Section 6.1). Pyrolysis of the chlorinated compound leads to a significant amount of HCI and also char. Very few chlorinated compounds are identified in the pyrolysate, since the elimination of HCI leaves very few chlorine atoms bound to carbons. Some aromatic hydrocarbons are formed by a mechanism similar to that of poly(vinyl chloride) pyrolysis. The elimination of HCI leads to the formation of double bonds, and the breaking of the carbon backbone leads to cyclization and formation of aromatic compounds. The reactions involved in this process are shown below for the case of formation of 1,3-dimethylbenzene ... 

The initial steps in oxidative reaction of aromatic, poly-aromatic and other cyclic and linear unsaturated hydrocarbons in the atmosphere or in combustion involve radical formation. These radicals react with molecular oxygen. The subsequent reactions of these peroxy radicals, as shown e.g. in Figure 4.1, result in unsaturated linear or cyclic, oxygenated or multi-oxygenated hydrocarbon intermediates. The thermochemistry for these unsaturated - oxygenated species is needed to evaluate their stability and likely reaction paths in the environment, in combustion and in other thermal and oxidative processes. 

The authors proposed a structural catalyst model based on the assumption of polymeric bonding of ruthenium metal clusters through the formation of ruthenium-aromatic ring bonds [259]. The validity of this contention was confirmed by synthesis of ruthenium complexes based on poly-1-vinylnaphthalene instead of polystyrene. It was demonstrated that both catalytic ruthenium-containing systems are active in the hydrogenation of unsaturated bonds in olefins, mononuclear aromatic hydrocarbons,... 

In another approach, poly(aryl ether sulfones) were synthesized by the electrophilic Friedel-Crafts reactions of sulfonyl halides with aromatic hydrocarbons. The critical step in these polymerizations is the formation of the carbon-sulfur bond. High polymers were obtained, though they were not always completely linear. Carbonyl aryl carbon-carbon bonds are created in Friedel Craft reactions leading to poly(aryl ketones). 

Excimer formation has been found to be most prominent for small organic aromatic molecules such as benzene [13],p-xylene [14], naphthalene [15], anthracene [16], pyrene [17], perylene [18], stilbene [19], and others [20]. Some polymers that contain aromatic groups, such as polystyrene [21] and poly (ethylene terephthalate) (PET) [22], and polynucleotides such as cytosine and thymine [23] have also been shown to exhibit excimer emission. Excimer emission is, in fact, widely observed in aromatic hydrocarbons [20]. 

Periasamy et at. obtained aldehydes in good yield from poly-cyclic aromatic hydrocarbon radical anions prepared by the addition of sodium to the aromatic hydrocarbon in THF, followed by formylation with carboxylic acid esters or N,N-dialkyformamides. Reactions of sodium naphthalenide, -anthracenide and -phenan-threnide with ethyl formate yielded the corresponding aldehydes. Substituted naphthalenes e.g. acenaphthene and 2-methylnaphthalene are also formylated using A/,A/-dialkylformamides, but in low yields (20% and 26% respectively). 

Many authors elucidated functionalization of polymers containing reactive oxirane moieties. Epoxidized NR, BR, IR and/or the respective model hydrocarbons, poly (butadiene-co-isoprene, various epoxy resins, poly (2,3-epoxypro-pyl methacrylate) and its copolymers or grafted systems were mostly exploited. Stabilizers based on epoxidized unsaturated rubbers are of the top interest. The mechanism of the functionalization process was studied in details by means of 3,4-epoxy-4-methylheptane and 1,2-epoxy-3-ethyl-2-methylpentane as model compounds [289]. The ring opening of the asymmetric oxirane is regiospecific. Aliphatic primary amines attack the least substituted carbon atom and can be involved in crosslink formation. Aromatic primary and secondary amines are less reactive than aliphatic ones because of their lower basicity the attack on the least substituted carbon atom is however preferred too. 

As seen from Table 6.7.18, the thermal decomposition of poly(methacrylic acid) generates at lower temperature the anhydride, and at higher temperatures undergoes decarboxylation. It can be assumed that the process leads to the formation of unsaturated chains that further decompose to form small hydrocarbon molecules and some aromatic compounds. Residual carboxyl groups may be retained on some of these molecules. 

A spiro cyclic hydrocarbon compound, o-xylylene dimer, could also undergo R-ROP to give poly(o-xylylene) due to the formation of a stable benzyl radical and an aromatic ring (37). 

Difunctional Initiators The methodology for preparation of hydrocarbon-soluble dilithium initiators is generally based on the reaction of an aromatic divinyl precursor with two mol of butyllithium. Unfortunately, because of the tendency of organolithium chain ends in hydrocarbon solution to associate and form electron-deficient dimeric, tetrameric, or hexameric aggregates, most attempts to prepare dilithium initiators in hydrocarbon media have generally resulted in the formation of insoluble three-dimensionally associated species [70]. The reaction of meffl-diisoprenylbenzene with 2 mol of f-butyllithium in the presence of 1 equivalent of triethylamine in cyclohexane at -20 °C has been reported to form pure diadduct without oligomerization. Equation 7.11 [71]. This initiator in the presence of 5 vol% of diethyl ether for the butadiene block has been used to prepare well-defined poly(metliyl methacrylate)- -polybutadiene-fe -poly(methyl methacrylate). 

---