Supercritical carbon dioxide processing of conducting composites of polypyrrole and porous crosslinked polystyrene

Conducting composites (similar to 3 mm in thickness) of polypyrrole (PPy) and porous crosslinked polystyrene (PCPS) were prepared by first impregnating PCPS with iodine (I-2), and then contacting it with pyrrole (Py). Both these steps were carried Out with and without supercritical carbon dioxide. The use of supercritical CO2 as a solvent for I-2 and Py facilitated the transport and deposition of these substances in the pores of the permanently porous host and produced composites with conductivities as high as 10(-3) S cm(-1). Moreover, the deposition of I-2 in the pores could be controlled via the CO2 pressure. The bulk and surface conductivities of the composite exhibited percolation behavior with respect to the amount of the I-2 deposited. whereas the volume conductivity exhibited a stepwise transition at approximately 100 wt% PPy+I-2 complex formed (with respect to the original mass of PUS). Optical micrographs suggest that non-uniform distributions of PPy are obtained in the pores below this transition. The percolation threshold was as low as 10 wt% so that the stability and mechanical strength of the composites were approximately the same as those of the host PCPS. This was verified by TGA and compressive strength measurements. The temperature dependence of the conductivity conformed with Mott's variable-range hopping (VRH) model for three-dimensional electronic transport. However, the data could be correlated equally well with the CELT model. (c) 2006 Elsevier Ltd. All rights reserved.