Polythiophene, alkyl-substituted 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. 

The molecular weights of substituted polymers are typically low compared with parent polymers due to the bulky nature of the ring substituents, which can hinder polymerization however, solubility in common organic solvent is increased. Dao et al. [193] have studied the effect of alkyl substituents on the molecular weight of polyaniline. The molecular weight of chemically prepared poly(2-methyl aniline) and poly(2-ethyl aniline) was reportedly 7000 and 5000g/mol, respectively, which is 15-times lower than polyaniline (80 000) prepared under identical conditions. A similar effect of alkyl substituents was observed on molecular weights of polythiophenes [207, 208]. 

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