Unique difference in transition temperature of two similar fluorinated side chain polymers forming hexatic smectic phase: Poly{2-(perfluorooctyl)ethyl acrylate} and Poly{2-(perfluorooctyl)ethyl vinyl ether}

The surface properties of comb-shaped polymers with perfluorooctyl ethyl side-chains are strongly related to the ordered structure of the side-chains at the surface. In this work, the thermal behavior, liquid-crystalline structure, and functional group orientation of comb-shaped polymers containing perfluorooctyl side-chains with poly(acrylate) (PFA-C₈) and poly(vinyl ether) (PFAVE8) backbones are discussed based on DSC, synchrotron-source X-ray diffraction, and FTIR measurements. Despite the similar tilted hexatic smectic structures and packing entropies, the isotropization temperature, T_i, of the PFA-C₈ is significantly higher than the PFAVE8. Detailed characterization of the conformation, alignment, and organization of the perfluorooctyl side-chains indicate that the difference in T_i is related to the configuration of side-chains and interactions between the carbonyl groups along the acrylate backbone. The present findings show that the type of the linkage between the polymer backbone and fluorinated side-chain mesogens affects the conformation and plays an important role in determining thermal behavior.