BIPOLAR CONDUCTING POLYMERS - BLENDS OF P-TYPE POLYPYRROLE AND AN N-TYPE LADDER POLYMER

Bipolar conducting polymers, in which both hole transport and electron transport contribute to electronic conductivity, have been explored b y chemical template synthesis of p-type polypyrrole (PPy) in the matri x of an n-type conjugated ladder polymer, poly(benzimidazole-benzophen anthroline) (BBL). Transmission electron microscopy images of the cond ucting polymer blends show that 5-20 nm diameter x 100-180 nm long rod like PPy particles are randomly and homogeneously distributed in the B BL matrix, with connectivity of the PPy phase occurring at a volume fr action of about 0.17. The volume fraction dependence of conductivity o f the BBL/PPy blends did not exhibit a percolation threshold at volume fractions as low as 0.007 nor can it be described by percolation-type effective medium theory. Room temperature conductivities as high as 6 0-70 S/cm were observed in the blends compared to 2 S/cm in pure PPy. The enhanced conductivity and the nonpercolation nature of these blend s originate from bipolar charge transport involving both conjugated po lymer components of the blends. Existence of the oxidized (p-type) pol ypyrrole and reduced (n-type) BBL that facilitate bipolar charge trans port in these blends was established by cyclic voltammetry.