Aromatic-heterocyclic polymers characterization

Work in our laboratory in the past few years has been concerned with the use of acetylene chemistry, both to aid the processing of aromatic heterocyclic polymers and to pro-, vide such materials a method by which they could become tougher and more durable in structural applications. The most attractive feature of the acetylenic carbon carbon triple bond is its capability to undergo various ionic and free radical addition reactions, leading to highly fused thermally stable aromatic systems. This paper will review our work on acety-lene containing aromatic heterocyclic polymers with respect to synthesis and characterization, as well as some already determined mechanical properties as composites and adhesives. 

Since Robinson [1] discovered cholesteric liquid-crystal phases in concentrated a-helical polypeptide solutions, lyotropic liquid crystallinity has been reported for such polymers as aromatic polyamides, heterocyclic polymers, DNA, cellulose and its derivatives, and some helical polysaccharides. These polymers have a structural feature in common, which is elongated (or asymmetric) shape or chain stiffness characterized by a relatively large persistence length. The minimum persistence length required for lyotropic liquid crystallinity is several nanometers1. 

Double helical DNA is a water-soluble polymer that contains an electronically well-coupled stack of aromatic heterocyclic base pairs. This review describes efforts in our laboratory to characterize electron-transfer reactions between transition metal complexes bound by intercalation within the 7r-stack of DNA. Much information is available concerning the structure, synthesis, and methods of characterization of this polymer. Also, research in our laboratories has been directed toward describing the photophysical and photochemical properties of metal complexes bound to DNA. Using these metal complexes to probe the DNA 7r-way, we are now in a position to ask Is DNA a molecular wire ... 

Polybenzimidazoles are heterocyclic, thermoplastic and basic polymers characterized by at least one aromatic unit, which confers high mechanical and thermal stability (Tg > 400 °C). As already introduced, the most investigated basic unit of this class of polymers is poly [2,2 -(m-phenylene)-5,5 -bibenzimidazole]... 

In general, carbocyclic aromatic polymers yield more carbonized products than heterocyclic ones. Susceptibility of polymers to carbonization under pyrolysis conditions is characterized by the so-called coke number Van Krevelen concluded that the tendency for carbonization may be regarded as an additive resultant of the contributions of the individual functional groups in the monomer units. The contribution of a group is expressed in carbon equivalents contributed by each group to the coke residue, CR, per monomer unit ... 

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. 

Epoxy resins are among the most important of the high performance thermosetting polymers and have been widely used as structural adhesives and matrix for fiber composites. Epoxy resins are characterized by the presence of epoxide groups before cure, and they may also contain aliphatic, aromatic, or heterocyclic structures in the backbone. The epoxy group can react with amines, phenols, mercaptans. 

Brown, C.E. and Webber, 1, 1982. Unpublished results and also. Brown, C.E., Bezoari, M.D. and Kovacic, P. 1982. J. Polymer Science, 20, 1697 Characterization of aromatic polymers (benzenoid and heterocyclic) by cross-polarization, magic-angle C-13 NMR spectroscopy. 

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