Variable polymer properties driven by substituent groups: Investigation on a trifluorovinylether-functionalized polyfluorene at the C-9 position

A new polyfluorene PF-TFVE with functional trifluorovinylether (-OCF=CF₂) groups at the C-9 position is reported. When heated to high temperatures, the polymer converts to a cross-linked network (PF-PFCB), which exhibits much lower dielectric constant and dissipation factor at high frequency than a traditional octyl substituted polyfluorene (PFO) (cf., PF-PFCB: 2.42 and 0.048; PFO: 3.80 and 0.22 @ 30 MHz). The electronic spectra of PF-PFCB indicate that it exhibits weaker UV-vis absorption and photoluminescent emission than PFO in the solid state, suggesting that the big substituent groups and the cross-linked networks in PF-PFCB hinder the conjugation between two fluorene units. This is the first example revealing that dielectric properties of polyfluorenes can be varied by different substituent groups at the C-9 position. These results indicate that polyfluorenes can not only be considered as semiconductors, but also as insulators. (Graph Presented).