Effect of Copolymer Composition on Electronic Conductivity of Electrochemically Oxidized Poly(3-hexylthiophene)-b-poly(ethylene oxide) Block Copolymers

Abstract

This is a study of the effect of copolymer composition on the electronic conductivity of poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-b-PEO) block copolymers. A wide variety of P3HT-b-PEO block copolymers with P3HT volume fraction ranging from 0.28 to 0.86 were synthesized. Lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt was added to the P3HT-b-PEO copolymers to enable electrochemical oxidation. Three terminal electrochemical cells were used to oxidize the P3HT microphase; the two outer electrodes were used to oxidize P3HT, while a nickel mesh located within the P3HT-b-PEO enabled measurement of electronic conductivity by ac impedance. Symmetric block copolymers with P3HT volume fractions in the vicinity of 0.5 exhibited the highest electronic conductivity in the oxidized state. The symmetric copolymers also exhibited the highest crystallinity. The intrinsic conductivity of oxidized P3HT microphases increases exponentially with increasing crystallinity.