Characterization and kinetics of mesophase transition for naphthalene-based thermotropic polyesters with polymethylene spacers

Main‐chain thermotropic polyesters containing naphthalene rings and flexible spacers with 2 ≤ n ≤ 10 methylene groups were prepared in this study. Their thermotropic properties were investigated by means of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The nematic mesophase dominates the anisotropy of the prepared polymers except for the polymers with n = 7 and n = 9. Moreover, the nematic domain size depends upon the number n. On the other hand, the naphthalene ring in the mesogen has a strong effect on the mesomorphic properties of the prepared polyesters. The polymers with n = 7 and n = 9 exhibit cooling rate‐dependent anisotropic behavior of nematic and smectic phases. The crystallization for the investigated polymers is strongly influenced by the anisotropic behavior. The kinetics of crystallization at higher temperatures does not satisfy the Ozawa theory, while it does at lower temperatures. Nucleation begins to occur in the nematic shreads and the crystal growth proceeds toward liquid‐crystalline domains from the observation by POM. Thus, the Avrami exponent a is dependent upon the polymethylene spacer with n being even or odd and high or low. In addition, the parameters of crystallization obtained from DSC and X‐ray diffraction were consistent with the results of non‐isothermal crystallization kinetics and the observation by POM.