Abstract
A chiral fluorene homopolymer (PF) and two new chiral alternating polyfluorenes, poly(fluorene-alt-benzothiadiazole) (PFBT) and poly(fluorene-alt-dithienylbenzothiadiazole) (PFDTBT), have been synthesized by palladium-catalyzed Suzuki polycondensations. In these polymers, chirality was introduced by attaching (S)-3,7-dimethyloctyl substituents to the 9-positions of the fluorene monomers. Upon thermal annealing, PF and PFBT undergo an irreversible phase transition to a liquid crystalline state that upon cooling to room temperature is vitrified and exhibits considerable circular dichroic (CD) effects. By contrast, PFDTBT forms an amorphous glass with hardly any CD activity. After fractionation by preparative size exclusion chromatography (SEC), the phase behavior of the low polydispersity polymers was studied by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and CD spectroscopy. Remarkably, after fractionation also for PFDTBT a CD effect was observed and for all three materials ...
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