Sulfonated polyimide as a thermally stable template for water processable conductive polymers

Abstract

Herein, sulfonated polyimides are utilized as a template for the polymerization of pyrrole (Py), aniline (ANi) and 3,4-ethylenedioxythiophene (EDOT) in order to produce their corresponding conductive polymers as stable processable aqueous dispersions. With polyimides having high thermal stabilities, the use of sulfonated polyimides (SPI) as templates imparts higher thermal stabilities on their water processable conductive polymers in comparison to their counterparts using polystyrenesulfonate (PSS) templates allowing for annealing temperatures approaching 300°C. This factor is of importance; in that it is comparable to processing temperatures of conventional polymers when these conductive polymers should be used in conductive composite materials, and for advancing developments in further increasing the electrical conductivities of these materials by studying the effects of annealing and the use of additives in a higher temperature regime.The PEDOT–SPI polymer exhibited superior conductivities (10–1000 fold) than the PEDOT–PSS polymer after processing at room temperature (RT) and after annealing at elevated temperatures (180°C, 300°C). The PEDOT–SPI system also showed 20 fold, 50 fold and 6 fold increases in conductivity after RT, 180°C and 300°C processing respectively, relative to the conducting polymers PEDOT–SPAA and PEDOT–SPI (from thermal treatment of SPAA) derived from the corresponding sulfonated polyamic acid (SPAA) and EDOT. The PANi–SPI polymer displayed the highest room temperature conductivity but lost considerable conductivity after high annealing temperatures of 180°C and 300°C. The PPy–SPI polymer systems revealed better conductivities after room temperature processing and elevated annealing temperatures, 180°C and 300°C (40×, 10×, 50×, respectively), than the PEDOT–SPI system. Secondary dopants (such as DMF), when used at 0.1wt.% DMF and annealed at 180°C/10min, affected a 100 fold improvement in conductivity (5.94×10−1S/cm versus 4.0×10−3S/cm of PEDOT–SPI). Furthermore, PANi–SPI doped with 0.1wt.% DMF showed the highest conductivity (2.51S/cm).