Conjugated polymers with solubilizing substituents

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]. 

Through the hybrid incorporation and copolymerization of various conjugated units, the electronic and electrochromic properties of the resulting polymers can be varied to cover colors across the entire visible spectrum. In this manner, the advantages of different conjugated vmits (i.e., low oxidation potential or solubilizing substituents) can be utilized while playing on the interaction of the comonomers (i.e., with the donor-acceptor systems). 

The discovery that conjugated polymers can be solubilized with appropriate substituents has given access to single chain properties. The volume of work devoted to the synthesis of new soluble materials has may be reached or even overpassed that devoted to the control of the solid phase through Ae polymerization. In this part we focus the attention on substituted polyacetylene, poly o diene and polydiacetylene, which have been the most investigated. 

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