Phase identifications and monotropic transition behaviors in a thermotropic main-chain liquid crystalline polyether

A thermotropic liquid crystalline (LC) polyether was synthesized by condensation polymerization of 1-(4-hydroxyphenyl-2-(2-methyl-4-hydroxypheyl)ethane) and α,ω-dibromononane, and abbreviated as MBPE-9. Multiple phase transitions were found via differential scanning calorimetry (DSC) upon heating and cooling. Based on wide-angle X-ray diffraction (WAXD) and polarized light microscopy (PLM) experiments, two monotropic LC nematic (N) and smectic phases and three crystalline (orthorhombic K₁, triclinic K₂ and triclinic K₃) phases were identified. A study on kinetics showed that only when the N phase formation rate was faster than the crystallization rate of K₁ phase which directly grew from the melt, the presence of the N phase could accelerate both the overall crystallization and the linear crystal growth rates of K₁ phase. In a narrow temperature region, two distinct crystal growth rates could be observed: one was directly from the isotropic melt, and another was from the N phase.