Interfacial synthesis and widely controllable conductivity of polythiophene microparticles

Fine polythiophene (PTh) microparticles were successfully synthesized by a novel interfacial polymerization at a dynamic interface between two immiscible solvents, i.e., n-hexane and acetonitrile or nitromethane containing thiophene and oxidant, respectively. The polymerization yield, size, and electrical conductivity of the microparticles are optimized by facilely regulating the medium species, oxidant species, oxidant/monomer ratio, monomer concentration, and polymerization temperature. The microparticles were thoroughly characterized by IR, UV-vis spectroscopy, wide-angle X-ray diffractometry, laser particle-size analyzer, and simultaneous TG-DSC technique. The yield rises with increasing oxidant/monomer ratio, monomer concentration, and polymerization temperature. However, low monomer concentration, low polymerization temperature, and modest oxidant/monomer ratio are all favorable for the formation of the PTh with good, large pi-conjugation and high conductivity. With decreasing the thiophene concentration from 200 to 50 mM at a fixed FeCl3/thiophene molar ratio of 3 at 0 degrees C in hexane/nitromethane biphase system, the PTh obtained exhibits a steadily enhanced conductivity from 10(-12) to 0.01 S cm(-1) and gradually darkening color from crimson to black. Under the same conditions, the PTh obtained in hexane/acetonitrile usually possesses lower yield but higher conductivity than that in hexane/nitromethane. The conductivity will be further enhanced to 1.1 and 4.4 S cm(-1) if the PTh powders are doped in iodine vapor and simply carbonized at 25 through 999 degrees C in nitrogen, respectively. The PTh is fine particles with the number-average diameter of 2.67-3.95 microm and low size polydispersity index between 1.12 and 1.23. The black particles carbonized at 25 to 999 degrees C are much smaller than original PTh particles, with the number-average diameter of 279 nm and size polydispersity index of 1.09. This interfacial approach provides an optimal synthesis of unique PTh microparticles with large pi-conjugation, high conductivity, black color, uniform size, good insolubility, excellent infusibility, high thermostability, and high yield of electrically conducting char at 999 degrees C.