Aromatic-heterocyclic polymers solubility

Many heterocyclic polymers have been produced in an attempt to develop high-temperature-resistant polymers for aerospace applications. Among these are the polybenzimidazoles (PBIs), which are prepared from aromatic tetramines and esters of dicarboxylic acids (structure 4.63). In standardized procedures, the reactants are heated to below 300°C forming soluble prepolymer, which is converted to the final insoluble polymer by further heating ... 

An alternative solution to the workup issue relied on the attachment of CH-acidic compounds 64 to a soluble polymer support (PEG-4000). The approach improved the yields of the dihydropyrimidinones 66 by the use of a 2-fold excess of other components—urea and aldehyde in the microwave-assisted solvent-free cyclocondensation [118]. Another single-step approach towards 4,5-disubstituted pyrimidines was based on cyclocondensation of a variety of aromatic, heterocyclic and aliphatic ketones, formamide and HMDS as the ammonium source [119]. The high temperature (215 °C) required to effect the formation of pyrimidines was secured by microwave dielectric heating in sealed vessels (Scheme 45). 

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 ... 

The solubility of a polymer depends on the solvent-solute (polymer) interactions, which must be greater than the solute-solute and solvent-solvent interactions. A polymer can be solubilised by a solvent with similar solubility parameters if certain polymer-solvent interactions are present between them. Polymers with flexible chemical linkages such as -0-/-S- or linear structures, have a better solubility than polymers with rigid linkages such as -N=N-, -C=C-, -C=N-, aromatic, heterocyclic, ladder or cross-linked structures. Similarly, amorphous and flexible polymers have better solubility than crystalline or rigid polymers. 

Unfortunately, wholly aromatic and/or heterocyclic polymers are notoriously difficult to process because they (1) exhibit low solubilities in common organic solvents and (2) typically start to decompose at a lower temperature than they melt. Attempts to improve the processing characteristics of... 

Both negative and positive tone aqueous developable materials have been introduced. Negative tone materials have been derived from tbe covalent-type polyamic ester precursors through the use of additives that enhance solubility of the unexposed film in aqueous developers (53). Positive tone materials are based on either polyamic ester precursors containing carboxylic acid (54) or phenolic oxygen substituents (55,56) or on aromatic poly(ortho-hydroxyamides) as precursors to polybenzoxazoles (57,58), a class of high temperature stable, heterocyclic polymers with thermal and mechanical film properties similar to polyimides (Fig. 18). In both approaches, the acid-base reaction of the phenolic or carboxylic... 

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. 

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