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 phas e separation, coalescence, and annihilation of liquid crystal textures duri ng 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 polar izing microscope. After the melting of monomers, the reaction system starte d from a homogeneous phase and then changed into a heterogeneous one. The f ollowing morphological changes during the entire reaction were observed: ge neration of anisotropic phase, coalescence of liquid crystal domains, forma tion of schlieren texture, annihilation of disclinations, and formation of stripe texture. We found all the liquid crystal domains formed in the isotr opic melt during the early stage of our polymerization reactions had the di sclination strength of +1. The number of defects decreased with increasing reaction time through coalescence and annihilation. At the early stage of p olymerization, the dominant factor affecting annihilation rate was the visc osity characteristics at elevated temperatures.