Synthesis of 4,4′-bis(nonafluorobiphenyl-4-oxyphenyl)- 1,4-oxytetrafluorobenzene and ladder spirobisindane-containing polyether on its base - I. M. Tkachenko; Ja. L. Kobzar; V. V. Kravchenko; O. V. Shekera; V. V. Shevchenko (Reports of the National Academy of Sciences of Ukraine, 2016)