Facile Synthesis of Solubilizing a Group-Free, Solution-Processable p -Type Ladder Conjugated Polymer and Its Thermoelectric Properties.

Here we report the synthesis of a new solubilizing group-free, solution-processable p -type ladder conjugated polymer, 6 H -pyrrolo[3,2- b :4,5- b ']bis[1,4]benzothiazine ladder (PBBTL) polymer by using a polyphosphoric acid (PPA) and phenylphosphonic acid (PhPO 3 H 2 ) 1:1 binary acid solvent system together with careful control of reaction kinetics. With a good intrinsic viscosity of 3.69 dL/g in methanesulfonic acid (MSA), good quality PBBTL films can be obtained via spin-coating. Intrinsic thin film properties and thermoelectric performance of PBBTL were evaluated, making it the second solubilizing group-free, solution-processable ladder-type conjugated polymer after BBL to be used for thin-film polymer electronics. While our preliminary thermoelectric performance of the FeCl 3 -doped PBBTL films is modest, we believe that many opportunities lie ahead for PBBTL and hope that its successful synthesis using the new PPA:PhPO 3 H 2 binary acid solvent system will inspire synthetic organic chemists to relook into solubilizing group-free, solution-processable ladder-type conjugated polymer systems.