Copolymerizations at various feed ratios between azo-dye-substituted thiophenes and
3-hexylthiophene under FeCl3-based oxidative conditions have been conducted. It is shown that when
the molecular structure of the dye is properly designed, completely soluble copolymers, with molecular
weigths ranging around 104 as Mn and dye-substituted monomer content up to 50% in a molar ratio, may
be prepared, as well as a completely soluble homopolymer. In addition, the so-obtained polymers evidenced
excellent filmability from a variety of solvents. The dye-substituted monomer content of the soluble
copolymers has been assessed by 1H NMR analysis via a convenient choice of the reference signals. In
the completely soluble copolymers the dye-substituted monomer content is well correlated to the feed
within a range between 0 and 75% of dye-substituted unit in the feed, which corresponds to a 0-50%
range in the copolymer composition, still conserving satisfactory molecular weights. Following these
observations and analyzing the characteristics of the polymers, a lower reactivity of the dye-functionalized
unit toward 3-hexylthiophene was evidenced in the used reaction conditions, and some hypotheses on
this finding are presented
