Conformation of a Polyfluorene Derivative in Solution

Abstract

The molecular weight and temperature dependencies of the intrinsic viscosity [η] were investigated for poly{2,7-[9,9-bis((S)-3,7-dimethyloctyl)]fluorene} (PDMOF) in tetrahydrofuran (THF). By analyzing the [η] data in terms of the touched-bead wormlike chain model, we estimated the persistence length q of PDMOF. It is 9.5 nm at 20 °C and slightly increases with decreasing temperature. The results of q were compared with the theoretical ones calculated on the basis of the broken wormlike chain (BWC), rotational isomeric state (RIS), and freely rotating chain (FRC) models. The BWC model for helical polymer chains gave q much larger than the experimental values, when the excess free energy ΔGr of the helix reversal for PDMOF was assumed to be comparable to those for typical synthetic helical polymers reported so far. On the other hand, the FRC model slightly underestimated the experimental q. A good fit to the experimental q was obtained for a simple RIS model where each monomer unit takes independently four rotational states, right- and left-handed 5/2 and 5/1 helical states, and its bond angle fluctuates slightly.