Cyclic Ladder Polymers Based on 5,5’,6,6’-Tetrahydroxy-3,3,3’,3’-tetramethylspirobisindane and 2,3,5,6-Tetrafluoropyridines
AbstractSilylated 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, crosslinked 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 imbalance. TFP yielded odd- and even-numbered cycles in both solvents NMP and sulfolane, and even the strained cyclic dimer was formed, indicating a rather high flexibility of these ladder polymers. Linear oligomers having degrees of polymerization (DPs) around 10 or 15 were prepared
from CTFP by means of substituted catechols as chain stoppers. Equimolar mixtures with cyclic ladder polymers did not indicate a selective detection of cycles by MALDI-TOF mass spectrometry.