Fluorinated Poly(pentylene 4,4′-bibenzoate)s with Low Isotropization Temperatures and Unique Phase Transition Behavior

High Resolution Image Download MS PowerPoint Slide Semiflexible main-chain thermotropic liquid crystalline polyesters (TLCPs) are applied in functional materials like heat dissipation sheets because of their good processability and ability to form nanostructures. Poly(pentylene 4,4′-bibenzoate) ( BB-5 ) is a commonly investigated biphenyl-based TLCP that forms a SmC A phase. The functional application of BB-5 is limited by its high isotropization temperature ( T i ). This study aims to lower the T i of BB-5 and enhance the processability of poly(pentylene 4,4″-terphenyl dicarboxylate) ( T-5 ) compounds, which contain photo/electronic functional mesogens. Six fluorinated BB-5 ( F-BB-5 ) compounds are synthesized with T i values at least 35 °C lower than that of BB-5 . Fluorinated T-5 ( F-T-5 ) compounds show isotropic phases before thermal decompositions, unlike T-5 . Moreover, F-BB-5 and F-T-5 form not only amorphous and SmC A phases but also crystalline and higher-order smectic phases, which is unexpected from low-molecular-weight liquid crystals. Mesogenic fluorination of semiflexible TLCPs results in low T i and even unique morphologies, opening up their new possibilities.