Phase separation and coalescence, annihilation of liquid crystal textures during polymerization of main-chain liquid crystalline polyesters

Using a novel thin film polymerization technique, we have observed the phase separation, coalescence, and annihilation of liquid crystal textures during polymerization of wholly aromatic main-chain liquid crystalline polymer poly(p-oxybenzoate/2,6-oxynaphthoate) (P(OBA/ONA)). The polycondensation reaction was conducted and observed in situ on the heating stage of a polarizing microscope. After the melting of monomers, the reaction system started from a homogeneous phase and then changed into a heterogeneous one. The following morphological changes during the entire reaction were observed: generation of anisotropic phase, coalescence of liquid crystal domains, formation of schlieren texture, annihilation of disclinations, and formation of stripe texture. We found all the liquid crystal domains formed in the isotropic melt during the early stage of our polymerization reactions had the disclination strength of +1. The number of defects decreased with increasing reaction time through coalescence and annihilation. At the early stage of polymerization, the dominant factor affecting annihilation rate was the viscosity characteristics at elevated temperatures.