LADDER POLYMERS BBL, BBB, PBT, PBO

The structures of these polymers, poly 7-oxo-, 10H-benz[de]imidazo[4 ,5 5,6]-benzimidazo[2,l-a]isoquinoline-3,4 10,1 l-tetrayl)-10-carbonyl (BBL), poly 6,9-dihydro-6,9-dioxobisbenzimidazo[2, lb 1 , lbenzo[ lmn]-[3,8]-phenanthroline-3,12-diyl (BBB), poly(p-phenylene-2,6-benzobisthiazolediyl) (PB7)andpoly(p-phenylene-2,6-benzobisoxazolediyl) (PBO) are shown schematically in Fig. 14-23. 

The reason they are called ladder polymers is because they may be considered derivatives of poly(acene), whose structure (Fig. 14-23) is characterized by two linear sideframes with interconnecting rung bonds, very much like that of a ladder. For our purposes, they do qualify as CPs, since they are possess a 7r-conjugated polymeric structure, and can indeed also be doped for greatly increased conductivity. The interest in these polymers has been due to their greater thermal and oxidative stability as compared to more conventional CPs, their facile processibility in their 

The chemical syntheses of BBL and BBT have been established for several decades [669], much before the advent of the field of CPs. As-synthesized polymer is usually dissolved in acids such as polyphosphoric acid or methanesulfonic acid for further processing. 

It has been found that prior to doping, these polymers conductivity can be enhanced by simple heat treatment- a form of thermo-mechanical annealing which increases alignment within the polymers [128], Thus. Wang et al. [128] found that 8 1 draw 

Doping has been carried out chemically [671], electrochemically [672] and via techniques such as ion implantation, a technique adapted from the semiconductor industry. Chemical doping, typically with SO3 or cone. H2SO4 vapor, yields conductivities of ca. 1 to 2 S/cm for BBL and BBB [673]. Interestingly, like P(PP), these polymers may also be n-doped. Thus, BBL, on doping with K-naphthalide, yields a conductivity of ca. 1 S/cm [673]. Bums et al. and Shacklette et al. [123, 657] adapted ion implantation techniques for Kr -ion implantation of BBL, PBO and PBT to obtain claimed conductivities of 220 S/cm for BBL and ca. 130 S/cm for PBO. 

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