Cyclic Ladder Polymers Based on 5,5`,6,6`-Tetrahydroxy-3,3,3`,3`-tetramethylspirobisindane and 2,3,5,6-Tetrafluoropyridines

Silylated 5,5‘,6,6‘-tetrahydroxy-3,3,3‘,3‘-tetramethylspirobisindane, TTSBI, was polycondensed with 2,3,5,6-tetrafluoropyridine, 4-cyanotetrafluoropyridine (CTFP), or pentafluoropyridine. In the latter case, cross-linked products were obtained even under mild conditions. All other polycondensations yielded soluble ladder polymers. N-Methylpyrrolidine or sulfolane was used as reaction media, and both time and temperature were varied. In NMP, a nearly quantitative conversion was achieved even at 60 °C. With the exception of the predominantly formed cyclic tetramer, even- and odd-numbered cycles were formed with equal probabilities. The formation of the cyclic trimer indicates a considerable flexibility of the ladder structure. In sulfolane the conversion was incomplete even at 100 °C, but only even-numbered cycles were formed (detectable up to 10 000 Da). Analogous polycondensations of 2,3,5,6-tetrafluoropyridine (TFP) suffered from its lower reactivity and high volatility, resulting in a stoichiometric imb...