LONG CHAIN ALKYL SUBSTITUTED POLY THIOPHENES

One of the first soluble CPs to be studied in detail were the poly (thiophenes) (P(T) s) substituted at the 3-position with long chain (up to octadeca-) alkyl groups, which rendered them amenable to reproducible solution (i.e. repeated solution/-dissolution) in organic solvents (such as chloroform), and thus processible, in their reduced, de-dopedforms [20,157, 259-261]. The same procedures used for chemical synthesis of P(T) s can be used for these as well, if one starts with the appropriate monomer. For instance, 3-octyl thiophene can be polymerized after iodination at the 

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LONG CHAIN ALKYL SUBSTITUTED POLY(THIOPHENES). .. 215... 

With regard to solvation of the de-doped forms of CPs, it may be perceived that this should be applicable to virtually all CPs as a means of processing. It is true that nearly all CPs show substantial solubility in organic solvents in their de-doped states. However, the highest MWt fractions frequently do not dissolve. Additionally, dissolution does not appear to be reproducible in all cases. For instance, if one dissolves a reduced P(Py) film in CHCI3, recasts the film, and attempts to redissolve the recast film, one loses a bit of the polymer in each such cycle, and one observes substantial degradation in electroactivity and other relevant CP properties. Only a few CPs, such as long-chain-alkyl substituted poly (thiophenes) (see below), are reproducibly soluble in this manner. 

It is evident that the use of solubilizing groups, such as the long alkyl chains for poly(thiophenes) or the long chain substituents for the P(DiAc) s described above, can render some measure of solubility or melt processibility to CPs. Indeed in one such example, Liu and Gregory [266] describe the chemical polymerization of a 3-urethane-substituted thiophene, to yield a P(T) soluble, albeit only in its de-doped... 

Since 3-substituted thiophene is easily synthesized, many studies have been devoted to its preparation and characterization. In particular, polythiophene bearing a long alkyl chain on the 3 position showed a very interesting structure and properties. Poly(3-dode-cylthiophene) was electrochemically prepared and the degree of polymerization was found to be 90 by vapor pressure osmometry [6,39]. Its conductivity was 67Scm . This is the first report on soluble conductive polymer. Poly(3-dodecylthiophene) showed bipolaron spectra in a chloroform solution and absorbance was linearly dependent on the concentration... 

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