Titration behaviors and spectral properties of hydrophobically modified water-soluble polythiophenes

The poly(3-thiopheneacetic acid) copolymers with 3-n-methylthiophene or with a 3-n-octadecylthiophene at the 3-position of a thiophene ring were synthesized. The solution and spectral properties of these hydrophobically modified polythiophenes have been studied by potentiometric titration, UV-visible spectroscopy. The effects of the rigid conjugated main chain, the steric hindrance and the hydrophobicity of a long alkyl side chain on the backbone conformational change have been discussed. We found that the conformational transition from the aggregate state to the extended state of the hydrophobically modified polythiophenes by the change of pH is sensitively restricted by the introduction of the hydrophobic alkyl or long alkyl side chains.