Poly(pyrrol-2-ylium tosylate): Electrochemical Synthesis and Physical and Mechanical Properties

Abstract

Polv(pyrrolylium tosylate) may be prepared by the electrochemical polymerization of pyrrole in acetonitrile utilizing tetraethylammonium tosylate as a supporting electrolyte without special precautions to exclude air. Pyrolytic carbon electrodes allow the use of high currents, which shortens preparative time (e.g., 80 mA, 3 V, 4 h) and yields large samples (50 mm X 90 mm x 0.13 mm). As-prepared poly(pyrrolylium tosylate) films contain 4-6% by weight acetonitrile and 2-3% water. When an applied potential of 3 V (≈80 mA) is utilized, films of composition [(C4H3N)(CH3CeH4SO3)0.143]nare obtained after removal of volatiles at 100 °C and 10-3torr for 18 h. This is the first time that an analytically pure, anhydrous, poly(pyrrolylium anion) film has been prepared without utilizing dry-atmosphere techniques. The analytical data show that neither irreversible oxidation nor hydrogenation of the pyrrole moiety occurs, even in the presence of water. The anion/polycation segmer ratio found for these films (0.43) is higher than that observed previously (0.28-0.32) and may be due to the higher applied potential utilized. Films of [(C4H3N)(CH3C6H4SO3)043]nare hygroscopic, taking up ≈3% water to form [(C4H3N)(CH3C6H4SO3)0.43]n•1/4H2O within 12 h. Slower water uptake continues, reaching ≈5% over the course of 3 months. This water absorption is reversible, the original composition being obtained after removal of water at 100 °C for 24 h. [(C4H3N)(CH3C6H4SO3)043]nexhibits a tensile strength of 69 MPa (1 X 104 psi), a Young's modulus of 2 GPa (3 X 105 psi), and an elongation-to-break of 8-18%. Acetonitrile/water, present in freshly prepared films, plasticizes poly(pyrrolylium tosylate) and reduces the modulus and tensile strength by1/3, while increasing the elongation-to-break to 50%. Poly(pyrrolylium tosylate) has been characterized by conductivity, X-ray, and SEM studies, as well as infrared, ESR, core-level X-ray photoelectron, and 13C NMR spectroscopy. The conductivity of the amorphous films (105 S cm-1) is only slightly affected on exposure to air over long periods of time (months). A variable-temperature study from 273 to 4.4 K showed that the conductivity of [(C4H3N)(CH3C6H4SO3)0.43]nfollows that predicted for a variable-range hopping mechanism and that the conductivity remains high (4.9 S cm-1) even at 4.4 K. The narrow ESR line (0.38 G) due to free spins present in [(C4H3N)(CH3C6H4S03)0.43]nis rapidly broadened on exposure to air but is narrowed back (0.5 G) almost to its original value after heating in vacuo overnight. The picture of poly(pyrrolylium tosylate) that emerges from the above studies is that of an easily prepared polymer film whose composition depends on the applied potential used for electropolymerization and the presence of adsorbed solvent/water. The mechanical properties are strongly dependent on the presence of solvent. While the conductivity of poly(pyrrolylium tosylate) is remarkably unaffected by exposure to air for long periods of time, physical and chemical changes that occur quickly (broadening of the ESR line, water uptake) and on a slower time scale (continued weight gain due to water absorption, attenuated spin density) are easily detected. © 1985, American Chemical Society. All rights reserved.