COMPATIBILITIES AND ELECTROSTATIC INTERACTIONS IN THE BLENDS OF SELF-ACID-DOPED CONJUGATED CONDUCTING POLYMER, POLY[2-(3'-THIENYL)ETHANESULFONIC ACID], AND ITS SODIUM-SALT WITH POLY(VINYL ALCOHOL)

The structure and properties of the blends poly[sodium 2-(3'-thienyl)e thanesulfonate] (P3TESNa)/poly(vinyl alcohol) (PVA) and poly[2-(3'-thi enyl)ethanesulfonic acid] (P3TESH)/PVA, both with a mole ratio 1/1 of the two components, were investigated by gel permeation chromatography (GPC), X-ray diffraction (XRD), infrared spectroscopy (IR), ultraviol et-visible-near-infrared spectroscopy (UV-vis-near-IR), X-ray photoele ctron spectroscopy (XPS), dynamic mechanical analysis (DMA), and condu ctivity. The blends were cast from water solutions of the two componen ts. The P3TESH/PVA blend consists of the two phases, a P3TESH phase an d a P3TESH/PVA complex phase, in which no characteristic of the PVA co mponent is observed. In the complex phase, the two polymers are intima tely mixed. However, this compatibility is different from that of conv entional polymer blends in that the present blend has an additional ph ase composed of one of the two pure components. The phase with the com plexes has glass transition and side chain relaxation temperatures hig her than that-of the pure components, and has new chain packing as ref lected in a new X-ray diffraction peak (2 theta) at 21.5 degrees. This type of compatibility results from the hydrogen-bonding (or electrost atic) interaction between the two components and the strong. aggregati on of one component (ill this case, P3TESH). The blending of P3TESH wi th PVA leads to a significant undoping, and the conductivity decreases from 10(-2) S/cm in the pure state to 10(-6) S/cm. The P3TESH subchai ns that are not self-acid-doped (or containing the -SO3H group) exhibi t a red shift of the W-vis absorption maximum by 44 nm, resulting from an increase in coplanarity caused by a repulsion between neighboring -SO3- groups. For the P3TESNa/PVA blend, the phase structure and elect rostatic interaction are similar to those in the above blend. A drasti c red shift of the W-vis absorption maximum by 76 nm (0.52 eV) accompa nied by a color change from pale orange-yellow to bright orange-red af ter the blending is observed. The red shift results from the strong el ectrostatic interaction between the Naf ion of P3TESNa and the O atom of PVA. Such a large red shift is equivalent to the thermochromism and solvatochromism of poly(3-alkylthiophene)s. The conductivity of P3TES Na (10(-7) S/cm) drops by 1 order of magnitude after blending with PVA , but the blend can be doped by aprotonic acid to give a conductivity of 10(-3) S/cm.