Rigid-Rod benzobisthiazole polymers with reactive fluorene moieties: Synthesis and characterization

High purity 2,7-fluorenedicarboxylic acid chloride was synthesized in a multistep reaction scheme from 2,7-dibromofluorene. Subsequent polycondensation in polyphosphoric acid of 2,5-diamino-1,4-benzenedithiol dihydrochloride with terephthaloyl chloride and 2,7-fluorenedicarboxylic acid chloride led to rigid-rod benzobisthiazole polymers with reactive fluorene moieties. The proportion of fluorene in the resultant polymers was controlled through reaction stoichiometry. Soluble polymers with intrinsic viscosities as high as 33.7 dL/g (methanesulfonic acid, 30°C) were obtained if the polymerization temperature was not allowed to exceed 165°C. Insoluble, presumably crosslinked polymers were obtained at higher temperature (190–200°C). Thermal characterization of the polymers by differential thermal analysis and thermal gravimetric analysis/mass spectroscopy did not disclose any thermal transition to 450°C. Onset of weight loss in air did not occur until over 550°C.