J . Am. Chem. SOC.1989, 1 1 1 , 4138-4139
4138
Electronically Conductive Polymer Fibers with Mesoscopic Diameters Show Enhanced Electronic Conductivities Zhihua Cai and Charles R. Martin*
Department of Chemistry, Texas A&M University College Station, Texas 77843 Received February 22, 1989 Polyheterocyclics have been the subject of intense recent research interest.' This interest seems from the fact that the oxidized forms of these polymers are electronically conductive. We have recently discovered that polyheterocyclics synthesized within the mesoscopic2 pores of a host membrane show dramatically enhanced electronic conductivities. Preliminary results of these investigations are reported in this correspondence. Polypyrrole (PP) and poly(3-methylthiophene) (PMT) were synthesized within the pores of Nuclepore membranes (10 pm thick; available from Nuclepore Corp., Pleasanton, CA); these membranes contain linear, cylindrical pores (Figure 1A). Synthesis was accomplished by allowing the membrane to separate a solution of the monomer from a solution of a chemical oxidizing agent. (For PP--0.6 M aqueous pyrrole and 2 M aqueous FeC13. For PMT-0.6 M 3-methylthiophene (CH3CN) and 1.0 M Fe(C104)3(CH3CN)). The monomer and oxidizing agent diffuse toward each other through the pores in the membrane and react to yield PP or PMT. This heterogeneous chemical synthesis proved to be more complicated (and interesting) than we had initially anticipated. The nascent conductive polymer nucleates along all of the surfaces of the host membrane. For example, Figure 1B shows an electron micrograph of a membrane after a brief (1 min) polymerization period. The irregular surface structure indicates that a layer of PP has deposited over the face of the membrane3 (compare Figure 1 (part A and B)). Electron micrographs of the opposite side of the membrane are identical. Figure 1 also indicates that the pores in the membrane have been partially filled with PP. (The pores in the virgin membrane, Figure 1A, were 1.O pm in diameter; after polymerization the pores were ca. 0.5 pm in diameter, Figure 1B.) Eventually, the pores become completely filled,4 and conducting polymer fibers are obtained. Thus, the first interesting feature of this heterogeneous chemical synthesis is that ultrathin-film (
