Liquid‐crystalline behavior and thermal conductivity of vinyl polymers containing benzoxazole side groups

Abstract

AbstractA series of methacrylamides containing benzoxazole (BO) mesogenic side groups and different lengths of alkyl units was synthesized in this study. A methacrylamide containing the n‐dodecyl group was selected as a suitable monomer to obtain beneficial thermally conductive polymeric materials because of its sufficient solubility in toluene in the subsequent radical polymerization and because of its liquid crystallinity. This methacrylamide led to a highly soluble polymer with film‐forming ability. The BO‐containing polymethacrylamide also exhibited liquid‐crystalline (LC) behavior during the heating and cooling processes. The cast film was kept at a slightly lower temperature than the clearing temperature and quenched to room temperature. This procedure afforded a film maintaining optical anisotropy at room temperature, implying that a frozen LC structure is maintained at room temperature. The quenched film also resulted in a significantly enhanced thermal conductivity (λ = 0.60 W m−1 K−1) without the aid of fillers and external fields, unlike the as‐cast counterpart without optical anisotropy. A polyacrylate containing a flexible long alkylene (C6) spacer between the main chains and a BO‐containing mesogenic side group was also investigated. The polyacrylate exhibited LC behavior during the heating and cooling processes over wide ranges. The polyacrylate film quenched from an established temperature, which contains a frozen LC structure, also exhibited a significantly enhanced λ value (0.63 W m−1 K−1) without fillers and external fields. Thus, the BO‐containing vinyl polymers studied in this work are promising candidates for novel heat‐releasing materials. © 2020 Society of Chemical Industry