Polythiophenes molecular weight

Regioregular intriniscally conducting mono-, di-, and triblock moderate molecular weight polythiophenes containing a well-defined terminus, (Vlll), were prepared by McCullough [7] and used in thin field-effect transitor applications. 

While the polymers seem to be amorphous in the solid state, there are signs of a transition in solution, possibly from a disordered coil state to a helix, which involves a temperature-dependent colour change 266). This change is also associated with precipitation of a partly-crystalline form. The crystals and solution apparently co-exist over a rather wide temperature range, which is unusual because polymers generally show a rather sharp transition from solubility to insolubility. This may reflect a broad distribution of molecular weights in the polythiophenes. 

It is important to clarify whether catalyst-transfer condensation polymerization is specific to polythiophene, or whether it is generally applicable to the synthesis of well-defined it-conjugated polymers. We investigated the synthesis of poly(p-phenylene), to see whether a monomer 28 containing no heteroatom in the aromatic ring would undergo catalyst-transfer polymerization. However, all polymers obtained in the polymerization with Ni(dppp)Cl2, Ni(dppe)Cl2, or Ni(dppf)Cl2 possessed low molecular weights and broad polydispersities. Nevertheless, we found that LiCl was necessary for opti-... 

As already pointed out above, electropolymerization has many variables which are difficult to control, and thus the structural parameters of the materials obtained tend to be variable. For example, depending on the electrochemical procedures used for the preparation of polythiophene, the conductivity can vary from 0.1 to 1000 S cm-1. This may be due to chain defects, the orientation of chains and the molecular weight the shorter the chain length, then the lower the conductivity is expected to be, since the conjugation is broken. 

Pd) or Fe(acac)328 as catalyst, the condensation reactions eventually leading to polythiophenes of low molecular weight. 

Despite their low molecular weights, these unsubstituted polythiophenes are insoluble in THF and other common organic solvents, and are also infusible. Their poor processability has therefore led to extensive studies of alkyl- and alkoxy-sub-stituted polythiophenes in the hope of enhancing solubility in organic solvents and allowing melt processing. Synthetic approaches to these substituted polythiophenes are described in the following text. 

KJine, R.J. et al.. Controlling the field-effect mobility of regioregular polythiophene by changing the molecular weight, Adv. Mater. 15, 1519, 2003. 

Yamamoto et a. [60-62] and Kurata et al [63] prepared polythiophene layers by vacuum evaporation. To ensure the deposition of poly- and not oligothiophenes, they removed low molecular weight material ( < 15-17) by Soxhlet extraction with CHCI3, The evaporated material is assumed to consist of poly-thiophene with a molecular weight of about 1500-2000 and 20-25 thiophene units. The X-ray and electron diffraction data of Yamamoto et al. point to a (partially) crystalline film with the polymer axes oriented perpendicular to a carbon or gold substrate plane if sub = 423 K. At lower substrate temperatures, the orientation and crystallinity are worse. This behaviour is not only true for the first deposited layer, but at least up to 10 layers, i.e, 100 nm. On polyimide substrates, however, the molecules lie on the substrate plane and orient along the rubbing direction of the polyimide [61]. 

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