POLYDIACETYLENES IN SOLUTION - CHARGED RODS AND NEUTRAL COILS

We report experimental results on several polydiacetylenes and a polythiophene in solution which demonstrate a change in charge state associated with solvatochromic and thermochromic transitions. The planar conformations are charged and the nonplanar conformations are neutral. When fields of ≈600 V/cm were applied to solutions of polymer in chloroform-hexane mixtures or toluene (i.e., the polymer is in the extended state), the polymers plated out on one electrode. We have measured the current as a function of time associated with the deposition of the polymer to determine the quantity of charge per polymer. The time dependence of the current had two regimes which can be associated with two types of charged material in the solution: the charged polymer, which plates out, and an unidentified charge transfer species which does not plate out. Polydiacetylenes 4BCMU and 3BCMU in solutions of chloroform/hexane became positively charged. Poly-3-hexyl-thiophene also became positively charged. PDA-9PA and PDA-92NA became negatively charged. We found a charge of 3×10-4 e/monomer for 4BCMU, 7×10-3 e/monomer for 3BCMU, and 4×10-2 e/monomer for PDA-9PA. Using this effect, we can demonstrate that both rod and coil segments coexist on the same polymer chain in the intermediate stages of the rod-coil transition. We suggest a mechanism which can qualitatively account for this unusual behavior. We also describe novel experiments in which an electric field was used to drive the polymers across a boundary between two nonmiscible solvents. When the polymer crosses the boundary, it changes color. The possibility of using the plating effect for precise fractionation by electrophoresis is suggested. © 1990 American Institute of Physics.