Investigation of the effect of an ether moiety on the liquid crystallinity by thin film polymerization

The effect of an ether moiety on liquid crystallinity was determined by means of in situ thin film polymerization under a polarizing microscope with a heating stage. The polymerization system consists of p-acetoxybenzoic acid (ABA)/acetoxyacetanilide (AAA)/4,4′-oxybis(benzoic acid) (OBA). Because of the swivel structure introduced by the ether group in the OBA monomeric unit, there is a critical composition to form the mesogenic phase during the polymerization. Liquid crystallinity forms when the concentration of the OBA is lower than 25 mol-%. Surprisingly, both LC phase and crystalline phase appear simultaneously in the isotropic phase if the reaction system is at critical composition. In addition, we have observed the disclination strengths change from ±1 to ±1/2 with an increase in ether linkages in the polymerization systems where LC phases appear, which is quite different from the homopolymerization system containing rigid rod-like p-acetoxybenzoic acid (ABA) and other systems without ether linkages where their disclinations have strengths of ±1. Clearly, the chain structure not only determines the formation of liquid crystallinity but also affects the strength of disclinations and the annihilation process.