Highly fluorinated aromatic-aliphatic copolyethers

A series of novel highly fluorinated aromatic-aliphatic copolyethers have been prepared by copolycondensation reactions of decafluorodiphenyl-sulfone (DFPSO) with hexafluoro-bisphenol-A (6F-BPA) and a highly fluorinated linear or branched diol (6CF-diol or 7bCF-diol) at different feed ratios of [diol]/[6F-BPA]. The reactions can be completed in 2-5 h in the presence of CsF in DMAc at room temperature to produce polymers with number average molecular weight (Mn) up to 45 000 Da. 1H and 19F NMR studies show that the composition of the resultant polymers agrees well with the feed ratio of the monomers in the reaction. This feature leads to a feasible tune of glass transition temperatures (Tg) and refractive indexes of the produced polymers by a simple control of the feed ratio. As the [diol]/[6F-BPA] ratio increases, the Tg of the copolymers decreases gradually from 185 to 87 \ub0C and 94 \ub0C, and the refractive index decreases from 1.5120(nTE)/1.5089(nTM) to 1.4643(nTE)/1.4629(nTM) and 1.4487(nTE)/1.4471(nTM) for the copolymers from 6CF-diol and 7bCF-diol, respectively. Meanwhile, the increase of the [diol]/[6F-BPA] ratio also effectively reduces the birefringence of the polymer films from 3.1 x10-3 to 1.4 x10-3 for the polymers from 6CF-diol and to 1.6 x10-3 for the polymers from 7bCF-diol. Well-developed waveguide structures with smooth ridge walls from these polymers have also been demonstrated using a cost-effective soft lithography technique.NRC publication: Ye