Polyphenylenes molecular weight limitations

In 1968 the Monsanto Company announced the availability of novel soluble low molecular weight polyphenylene resins. These may be used to impregnate asbestos or carbon fibre and then cross-linked to produce heat-resistant laminates. The basic patent (BP 1037111) indicates that these resins are prepared by heating aromatic sulphonyl halides (e.g. benzene-1,3-disulphonyl dichloride) with aromatic compounds having replaceable nuclear hydrogen (e.g. bisphenoxy-benzenes, sexiphenyl and diphenyl ether). Copper halides are effective catalysts. The molecular weight is limited initially by a deficiency in one component. This is added later with further catalyst to cure the polymer. 

In the Phillips process, polyphenylene sulfide (PPS) is obtained from the polymerization mixture in the form of a fine white powder, which, after purification, is designated Ryton V PPS. Characterization of this polymer is complicated by its extreme insolubility in most solvents. At elevated temperatures, however, Ryton V PPS is soluble to a limited extent in some aromatic and chlorinated aromatic solvents and in certain heterocyclic compounds. The inherent viscosity, measured at 206°C in 1-chloronaphthalene, is generally 0.16, indicating only moderate molecular weight. The polymer is highly crystalline, as shown by x-ray diffraction studies (9). The crystalline melting point determined by differential thermal analysis is about 285°C. 

Clearly, the connection of predeposited, low-molecular-weight precursors in a controlled manner, directly onto a surface through irreversible covalent bonding, offers the means to overcome the limitations of solution synthesis defined above. In fact, the present bottom-up route for the creation of atomically precise graphene nanoribbons and nanographenes from appropriate polyphenylene... 

In the reaction of bromo benzene with ethylene trans-stilbene is formed as the target product. The formation of cis stilbene is not found within the detection limit of gas chromatography. The limitation of the molecular weight in the polyreaction is mainly caused by the dehalogenation of bromo benzene. By optimization of the reaction conditions (low reaction temperature, low catalyst concentration) the dehalogenation is pushed back below the detection limits of gas chromatography. The main defect structures in the polymer are caused by 1,1-disubstitution. This deHciency in the regioselectivity of Ae reaction can not be suppressed even by optimal reaction conditions. Therefore polyphenylene vinylene obtained by Ae Heck reaction has statistically a fold in Ae macromolecule after 30 - 100 monomer... 

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