CHARACTERIZATION OF POLY(3-OCTYLTHIOPHENE) .1. MOLECULAR CHARACTERIZATION IN DILUTE-SOLUTION

The poly(3-alkylthiophenes) are a class of electrically conducting pol ymers which are of particular scientific and commercial interest due t o their solubility and meltabillty. A series of poly(3-octylthiophene) (P3OT) fractions having molecular weights in the range M(w) = 30,000 to 400,000 were generated by preparative gel permeation chromatography (GPC). Although the polymer remained weakly aggregated when dissolved in pure THF, the addition of an organic salt (1 wt.% tetrabutylammoni um p-toluenesulfonate) resulted in complete molecular dissolution. We were thus able to completely and consistently describe the polymer's s ingle-chain properties using three dilute solution characterization me thods: viscometry, GPC, and integrated light scattering. The molecular weight dependence of the intrinsic viscosity and the radius-of-gyrati on were established, and were characteristic of solutions near the the ta condition, indicating poor solvent quality. Calculation of the pers istence length from our data revealed that the polymer backbone is onl y 2 to 3 times more rigid than common flexible polymers, despite its c onjugated ring structure.