Multicyclic poly(benzonitrile ether)s based on 1,1,1-tris(4-hydroxyphenyl)ethane and isomeric difluorobenzonitriles

Silylated 1,1,1-tris(4-hydroxyphenyl)ethane (THPE) was polycondensed in N-methylpyrrolidone with either 2,6-difluorobenzonitrile or 2,4-difluorobenzonitrile under conditions allowing for complete conversions of the C-F groups. With 1.0:1.0 stoichiometry, completely soluble polyethers were obtained from both isomeric difluorobenzonitriles. The MALDI-TOF mass spectra proved tree-shaped and cyclic polyethers to be the main products. With a molar excess of 10%, the 2,6-difluorobenzonitrile gave a cross-linked product at a concentration of 15 mmol/30 mL (THPE/NMP) or cross-linking occurred with 20 mol % excess at a concentration of 4 mmol/30 mL. However, the 2,4-difluoro isomer yielded soluble polyethers even in an excess of 50 mol %. Such an excess of the difluoro monomer had the consequence that linear and tree-shaped polyethers were never formed, and multicyclic oligomers or polymers became the predominant reaction products, so that even with ideal stoichiometry gelation did not occur. Multicycles free of functional (end) groups were the main reaction products under optimum conditions. The reason for the different cyclization tendencies of 2,6- and 2,4-difluorobenzonitrile were discussed on the basis of computer modeling of different conformations.