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

Abstract

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 SmCA phase. The functional application of BB-5 is limited by its high isotropization temperature (Ti ). This study aims to lower the Ti 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 Ti 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 SmCA 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 Ti and even unique morphologies, opening up their new possibilities.

Preparation of fluorinated polyesters by reversible addition–fragmentation chain transfer step-growth polymerization

“…2,3 Consequently, fluorinated polyesters have shown great potential in textiles, antifouling coatings, optical waveguide devices, biomedical devices, etc . 2,4–15 Nevertheless, studies on fluorinated polyesters were few compared to other fluoropolymers, because of the difficulty in synthesis. 3…”