Conjugated polymers with solubilizing

Since the discovery that Poly-n-alkylthiophenes can be solubilized (15), they have been the subject Of intensive studies. The stability of the polymer together with the possibility to study the doped polymer in solution are die origins of the interest Besides, poly-n alkylthiophene films exhibit drastic change as shown with the thermochromism which varies widi the size of the substituent (Salaneck et al, this book). Moreover poly-n alkylthiophene provides an unique oppcntunity to investigate the chain conformation of a conjugal polymer with a conjugated backbone maiicedly different from the substituted polydiacetylene or polyacetylene. 

Similar to the other rigid aromatic polymers, the insolubility of polyphenylenes constitutes the major problem associated with their synthesis and characterization [5] indeed, this is the very reason why most polyphenylenes synthesized to date have been decorated with solubilizing side chains. Such substituents not only cause the dihedral angles to be detrimental for conjugation when connected at ortho positions (see Section 22.5.1), but they also dilute the main-chain properties, particularly in bulk. Consequently, the aim has been to reduce the side chain content as much as possible for certain applications. Bearing this in mind, Schliiter and coworkers have synthesized a variety of alkyl chain-substituted PPPs with systematically decreased densities of the side chains (Figure 22.22) [34]. 

Solvents Solvents serve multiple roles in the polymerization. They need to not only solubilize monomers and stabilize the catalyst, but also dissolve as-formed conjugated polymers. Poor solubility of synthesized polymers in the solvent system leads to premature precipitation of polymers before they reach the desirable high molecular weight. Solvents such as DMF and NMP with high polarity and good coordination ability are desirable since they can function as coordination ligands to the palladium and thereby help maintain the catalyst in the solution. However, conjugated polymers often suffer from low solubility in... 

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